How spaceships determine each other's mass in space?












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Set in the distant future, space travel becomes prominent and cheap. I can imagine each spaceship would have a multitude array of sensors to track distance and relative position in space, is there any good way to determine another spaceship's mass beside hailing them for specs?



I know we can accurately know the mass of an asteroid using Newton's law of universal gravitation and probably Kepler's law too, I guess, but that's only for orbiting object in space unlike a spaceship which usually accelerates using its own propulsion drive.



Please state down the principle of measurement and I would prefer economical solution.






technology space-travel spaceships







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    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    19 hours ago






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    @BinaryWorrier: why not? I cannot imagine the display screen shows the mass of every astronomical objects except other spaceship...
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    – user6760
    18 hours ago






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    @BinaryWorrier If you are an explorer encountering an alien ship you have never seen before, then you would want to know as much about it as you can. If you are a space pirate looking for booty, you don't want to waste your time with capturing an empty freighter. If you are law enforcement, you might have to enforce some spaceflight regulations where vessel mass is relevant ("If you want to enter geostationary orbit around this planet with a vessel mass over 10000 tons you need permit 87A/65 in triplicate").
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    – Philipp
    18 hours ago








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    You specifically exclude asking them, so I won't write this as an answer, but have you considered an automatic identification system? Currently, all aircraft and watercraft above a certain size are required to broadcast their identity and location (and probably more). A similar system for your spacecraft could also include current or nominal mass of the ship. This wouldn't work for alien or unauthorized craft, or for asteroids, but it would certainly help you identify all law-abiding vehicles.
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    – David K
    16 hours ago








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    "we can accurately know the mass of an asteroid using Newton's law of universal gravitation": this is true only if the asteroid has a satellite orbiting about it. What can be used is the Yarkovsky effect, but with current technology that requires a long period of observation.
    $endgroup$
    – Ray Butterworth
    16 hours ago


















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$begingroup$


Set in the distant future, space travel becomes prominent and cheap. I can imagine each spaceship would have a multitude array of sensors to track distance and relative position in space, is there any good way to determine another spaceship's mass beside hailing them for specs?



I know we can accurately know the mass of an asteroid using Newton's law of universal gravitation and probably Kepler's law too, I guess, but that's only for orbiting object in space unlike a spaceship which usually accelerates using its own propulsion drive.



Please state down the principle of measurement and I would prefer economical solution.






technology space-travel spaceships







share|improve this question











$endgroup$








  • 8




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    19 hours ago






  • 2




    $begingroup$
    @BinaryWorrier: why not? I cannot imagine the display screen shows the mass of every astronomical objects except other spaceship...
    $endgroup$
    – user6760
    18 hours ago






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    @BinaryWorrier If you are an explorer encountering an alien ship you have never seen before, then you would want to know as much about it as you can. If you are a space pirate looking for booty, you don't want to waste your time with capturing an empty freighter. If you are law enforcement, you might have to enforce some spaceflight regulations where vessel mass is relevant ("If you want to enter geostationary orbit around this planet with a vessel mass over 10000 tons you need permit 87A/65 in triplicate").
    $endgroup$
    – Philipp
    18 hours ago








  • 1




    $begingroup$
    You specifically exclude asking them, so I won't write this as an answer, but have you considered an automatic identification system? Currently, all aircraft and watercraft above a certain size are required to broadcast their identity and location (and probably more). A similar system for your spacecraft could also include current or nominal mass of the ship. This wouldn't work for alien or unauthorized craft, or for asteroids, but it would certainly help you identify all law-abiding vehicles.
    $endgroup$
    – David K
    16 hours ago








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    $begingroup$
    "we can accurately know the mass of an asteroid using Newton's law of universal gravitation": this is true only if the asteroid has a satellite orbiting about it. What can be used is the Yarkovsky effect, but with current technology that requires a long period of observation.
    $endgroup$
    – Ray Butterworth
    16 hours ago
















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$begingroup$


Set in the distant future, space travel becomes prominent and cheap. I can imagine each spaceship would have a multitude array of sensors to track distance and relative position in space, is there any good way to determine another spaceship's mass beside hailing them for specs?



I know we can accurately know the mass of an asteroid using Newton's law of universal gravitation and probably Kepler's law too, I guess, but that's only for orbiting object in space unlike a spaceship which usually accelerates using its own propulsion drive.



Please state down the principle of measurement and I would prefer economical solution.






technology space-travel spaceships







share|improve this question











$endgroup$




Set in the distant future, space travel becomes prominent and cheap. I can imagine each spaceship would have a multitude array of sensors to track distance and relative position in space, is there any good way to determine another spaceship's mass beside hailing them for specs?



I know we can accurately know the mass of an asteroid using Newton's law of universal gravitation and probably Kepler's law too, I guess, but that's only for orbiting object in space unlike a spaceship which usually accelerates using its own propulsion drive.



Please state down the principle of measurement and I would prefer economical solution.






technology space-travel spaceships




technology space-travel spaceships






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 11 hours ago









Glorfindel

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3951514










asked 21 hours ago









user6760user6760

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  • 8




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    19 hours ago






  • 2




    $begingroup$
    @BinaryWorrier: why not? I cannot imagine the display screen shows the mass of every astronomical objects except other spaceship...
    $endgroup$
    – user6760
    18 hours ago






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    @BinaryWorrier If you are an explorer encountering an alien ship you have never seen before, then you would want to know as much about it as you can. If you are a space pirate looking for booty, you don't want to waste your time with capturing an empty freighter. If you are law enforcement, you might have to enforce some spaceflight regulations where vessel mass is relevant ("If you want to enter geostationary orbit around this planet with a vessel mass over 10000 tons you need permit 87A/65 in triplicate").
    $endgroup$
    – Philipp
    18 hours ago








  • 1




    $begingroup$
    You specifically exclude asking them, so I won't write this as an answer, but have you considered an automatic identification system? Currently, all aircraft and watercraft above a certain size are required to broadcast their identity and location (and probably more). A similar system for your spacecraft could also include current or nominal mass of the ship. This wouldn't work for alien or unauthorized craft, or for asteroids, but it would certainly help you identify all law-abiding vehicles.
    $endgroup$
    – David K
    16 hours ago








  • 2




    $begingroup$
    "we can accurately know the mass of an asteroid using Newton's law of universal gravitation": this is true only if the asteroid has a satellite orbiting about it. What can be used is the Yarkovsky effect, but with current technology that requires a long period of observation.
    $endgroup$
    – Ray Butterworth
    16 hours ago
















  • 8




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    19 hours ago






  • 2




    $begingroup$
    @BinaryWorrier: why not? I cannot imagine the display screen shows the mass of every astronomical objects except other spaceship...
    $endgroup$
    – user6760
    18 hours ago






  • 16




    $begingroup$
    @BinaryWorrier If you are an explorer encountering an alien ship you have never seen before, then you would want to know as much about it as you can. If you are a space pirate looking for booty, you don't want to waste your time with capturing an empty freighter. If you are law enforcement, you might have to enforce some spaceflight regulations where vessel mass is relevant ("If you want to enter geostationary orbit around this planet with a vessel mass over 10000 tons you need permit 87A/65 in triplicate").
    $endgroup$
    – Philipp
    18 hours ago








  • 1




    $begingroup$
    You specifically exclude asking them, so I won't write this as an answer, but have you considered an automatic identification system? Currently, all aircraft and watercraft above a certain size are required to broadcast their identity and location (and probably more). A similar system for your spacecraft could also include current or nominal mass of the ship. This wouldn't work for alien or unauthorized craft, or for asteroids, but it would certainly help you identify all law-abiding vehicles.
    $endgroup$
    – David K
    16 hours ago








  • 2




    $begingroup$
    "we can accurately know the mass of an asteroid using Newton's law of universal gravitation": this is true only if the asteroid has a satellite orbiting about it. What can be used is the Yarkovsky effect, but with current technology that requires a long period of observation.
    $endgroup$
    – Ray Butterworth
    16 hours ago










8




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$begingroup$
Do you mind me asking . . . why would you need to know?
$endgroup$
– Binary Worrier
19 hours ago




$begingroup$
Do you mind me asking . . . why would you need to know?
$endgroup$
– Binary Worrier
19 hours ago




2




2




$begingroup$
@BinaryWorrier: why not? I cannot imagine the display screen shows the mass of every astronomical objects except other spaceship...
$endgroup$
– user6760
18 hours ago




$begingroup$
@BinaryWorrier: why not? I cannot imagine the display screen shows the mass of every astronomical objects except other spaceship...
$endgroup$
– user6760
18 hours ago




16




16




$begingroup$
@BinaryWorrier If you are an explorer encountering an alien ship you have never seen before, then you would want to know as much about it as you can. If you are a space pirate looking for booty, you don't want to waste your time with capturing an empty freighter. If you are law enforcement, you might have to enforce some spaceflight regulations where vessel mass is relevant ("If you want to enter geostationary orbit around this planet with a vessel mass over 10000 tons you need permit 87A/65 in triplicate").
$endgroup$
– Philipp
18 hours ago






$begingroup$
@BinaryWorrier If you are an explorer encountering an alien ship you have never seen before, then you would want to know as much about it as you can. If you are a space pirate looking for booty, you don't want to waste your time with capturing an empty freighter. If you are law enforcement, you might have to enforce some spaceflight regulations where vessel mass is relevant ("If you want to enter geostationary orbit around this planet with a vessel mass over 10000 tons you need permit 87A/65 in triplicate").
$endgroup$
– Philipp
18 hours ago






1




1




$begingroup$
You specifically exclude asking them, so I won't write this as an answer, but have you considered an automatic identification system? Currently, all aircraft and watercraft above a certain size are required to broadcast their identity and location (and probably more). A similar system for your spacecraft could also include current or nominal mass of the ship. This wouldn't work for alien or unauthorized craft, or for asteroids, but it would certainly help you identify all law-abiding vehicles.
$endgroup$
– David K
16 hours ago






$begingroup$
You specifically exclude asking them, so I won't write this as an answer, but have you considered an automatic identification system? Currently, all aircraft and watercraft above a certain size are required to broadcast their identity and location (and probably more). A similar system for your spacecraft could also include current or nominal mass of the ship. This wouldn't work for alien or unauthorized craft, or for asteroids, but it would certainly help you identify all law-abiding vehicles.
$endgroup$
– David K
16 hours ago






2




2




$begingroup$
"we can accurately know the mass of an asteroid using Newton's law of universal gravitation": this is true only if the asteroid has a satellite orbiting about it. What can be used is the Yarkovsky effect, but with current technology that requires a long period of observation.
$endgroup$
– Ray Butterworth
16 hours ago






$begingroup$
"we can accurately know the mass of an asteroid using Newton's law of universal gravitation": this is true only if the asteroid has a satellite orbiting about it. What can be used is the Yarkovsky effect, but with current technology that requires a long period of observation.
$endgroup$
– Ray Butterworth
16 hours ago












13 Answers
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A few options ordered from "difficult but can be done at any time" to "easy, but requires an opportunity".



Measure the gravitational lensing effect of the ship



Every mass in the universe bends the space around it. This can be observed because stars behind the object appear displaced. This is how current day astronomers estimate the masses of astronomic objects (planets, stars, galaxies...). With access to much more precise instruments it might be possible to use the same principle for much smaller masses.



If you are able to measure gravitational lensing around a regular sized space ship with current day technology, you know you are dealing with something with a really, really extreme density (neutron-star level)... or with something which uses artificial gravity technology. Anyway, it's definitely something based on technology far beyond anything you could comprehend. Proceed with caution!



Measure the effect of its gravity on nearby objects



If your instruments are not precise enough to measure its effect on light, you might still be able to measure its effect on dust clouds, micro-asteroids, space junk and other small objects when they get very close to the ship.



But again, if they use artificial gravity technology, then that might screw up your measurement. Also check if the objects you measure contain any magnetic materials. If the ship generates a magnetic field for some reason (which can be an unintentional by-product of all kinds of devices), then that might also affect nearby objects.



Measure its exhaust and the corresponding acceleration



I would like to expand on point 3 of the answer by Darth Donut. If the engines of the ship work according to Newtons 3rd law of motion (which is the only way space propulsion can work according to our current understanding of physics), the kinetic force of the exhaust is exactly the same as the kinetic force applied to the ship. So when you observe the ship while it performs an acceleration burn, you can observe how much exhaust mass it expels per second and with what velocity. Multiply the two and you have its engine thrust. Divide the thrust by the acceleration of the ship you observe, and you have the mass of the ship.



Measure how it behaves when hit by another object



The ship is too light to cause any observable gravity effects and doesn't feel like performing any maneuvers right now? There is another way to apply Newton's laws to examine its mass. Wait until it gets hit by a micrometeroid. Measure the mass and acceleration of the meteroid and see how much the ship's velocity changes when it gets hit. When no meteroids are around, you could of course launch a known mass with a known acceleration at the ship yourself. But that might be perceived as impolite.






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    "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
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    – DarthDonut
    20 hours ago






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    "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
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    – Kepotx
    19 hours ago






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    How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
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    – Nuclear Wang
    16 hours ago






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    @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
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    – Philipp
    16 hours ago






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    @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
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    – Brilliand
    7 hours ago



















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Here are a few ideas I got:



1. Look up the ship type:

As long as this ship you are seeing is not made by a to date unknown civilication, your databases should be able to identify the ship type, and show you some basic information for that.



2. Estimate by size:

As long as you can measure the distance, you can measure the size of such a ship. Now, your engineers will have an estimate for how much space is taken up by machinery, how much mass is used for the hull, how much space is needed for crew and so on. They know what materials are used commonly, and by multiplying the estimated volume with an average density you can estimate the mass of the ship. It is not a precise estimate, but your engineers should be pretty near to the exact value.



3. Measure the acceleration and energy output of the engines:

Every engine known to us emits radiation in some form due to conversion losses. As long as you can measure the acceleration of such a ship, the radiation of the engines and can identify the type of engine, you should be able to get a good estimate how much energy is used to power the engine, how much force the engines generate and in turn how much mass the ship has.



Everything you need for the above methods are good optical sensors and radiation sensors.






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    good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
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    – Kepotx
    20 hours ago






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    wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
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    – Kepotx
    20 hours ago






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    @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
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    – DarthDonut
    20 hours ago








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    By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
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    – Kepotx
    19 hours ago






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    Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
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    – Separatrix
    18 hours ago



















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The vacuum of space act as a dielectric.



If you are close enough, provide a net electric charge to your own ship. This will induce a charge also on the probed ship, and will trigger an electrostatic attraction between the two.



Measure your velocity with respect to background and your velocity with respect to the probed ship.



Since you know the charge involved and you can determine the resulting force exerted on the probed ship. The resulting force will change your velocity and the one of the probed ship. You know your mass and your velocity both with respect to background and to probed ship, the only unknown parameter is the probed ship mass.






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    What If the're also doing the same thing? It could affect the measurement...
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    – user000001
    12 hours ago








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    How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
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    – WGroleau
    9 hours ago





















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Probe indirectly



Launch a small probe of precisely known mass so that it passes at a known distance from the ship. The probe might be as opaque and undetectable as could be. At a predetermined moment the probe shoots a low-power laser signal to the mothership, allowing its position to be precisely determined. From there, you can work back the deflection on the trajectory caused by the gravitational mass of the unknown ship.



Probe (almost) directly



Send two probes at different distances from the unknown ship, depending on how sensitive their gravitational sensors are. Measure acceleration on both probes. These will be caused by all nearby masses (the mothership included), but using two probes, the residual that has quadratic dependency on the unknown ship's distance once the other masses are ruled out will give the unknown ship's mass.



For example if all other masses are sufficiently far away, the distance between them and probes P and Q may be taken as constant, so the differential will be zero. The acceleration on probe P will then be given by G(M/a^2 - X/(b+d)^2) while that on probe Q by G(M/(a+d)^2 - X/b^2), with M and X the masses of the mothership and the unknown's, a and b the distances of the first probe from the mothership M and the unknown, and d the distance between the probes:



     M            P         Q                                        X

     |--- a ------|--- d ---|--------------------- b ----------------|


Assuming b, especially, is known with sufficient accuracy (phased laser ranging, maybe?) and accelerometers of sufficient precision are available, the two probes could even be mounted on a fixed "antenna" (it is not necessary for M, P, Q and X to be aligned on a line, but this simplifies things).






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    Shoot them with a powerful laser and see how much the momentum of their ship changes.



    You didn't mention anything about leaving the ship intact.






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      Sounds good until you find out they have a more powerful laser.
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      – prl
      11 hours ago






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      @prl "If you must swing first, swing hard.. and connect."
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      – Cort Ammon
      1 hour ago



















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    Shine a laser at it, and measure the (exceedingly slight) change in momentum.




    Several years later, in 1922, physicist Arthur Compton performed an
    experiment which led to the discovery of the Compton Effect. Proving
    Einstein correct, Compton showed that photons indeed have momentum
    which is transferrable to materials that have a mass. Compton was
    awarded the 1927 Noble Prize in Physics for demonstrating that photons
    can transfer their momentum to the electrons with which they collide
    inside an atom.




    I am, of course, assuming that by the time there are enough spaceships out there that one needs to worry about determining their mass, we will have the technology to be able to detect very minute changes in momentum that a laser beam would impart on a ship. Yes, I am aware that it would be easier to detect the change in momentum caused by a flea smacking into a super jumbo jet, but hey, we are talking about the future here.






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      It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
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      – prl
      11 hours ago










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      @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
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      – Justin Thyme
      5 hours ago



















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    Scan them. Fire a very large burst of neutrinos at them and measure how much gets reflected back. In general the more massive an object is the more return signal you will get. It works okay for an estimated order of magnitude.



    Unlike other answers this probably won't be recognized as an act of violence, doesn't disturb their trajectory and gives you an answer near to light speeds.



    Edit: Actually, I'm no physicist but I think you won't get neutrinos back, you might get electrons, but I'm just not knowledgeable enough to say for sure.






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      Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
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      – Mark
      9 hours ago



















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    In Civilized Areas, They will Tell You Automatically



    Today, ships and aircraft have systems that self report their name, size, exact location, velocity, destination etc. For ships, this is AIS, and for aircraft it is ADS-B. The systems automatically squawk their info a regular intervals, so as soon as you are in receiving range you know what the contact picture is.



    It is often required by the relevant authorities, as it significantly improves safety when everyone knows where everyone else is.



    Otherwise, IR will give a Good Guess



    All vessels will have a power source. This power source is going to have waste heat, which will radiate from the vessel evenly. (Unless the owner pumps air/fluids around to deliberately alter the heat transfer.) This waste heat will be subject to one over r squared losses. If you can determine a range, you can determine how much this blackbody radiation will have dropped off, and you can get an estimate of the size of the power source.



    Power is going to be strongly related to vessel size and acceleration. The exact equation is probably going to be complex, but luckily the universe is full of vessels providing you with empirical data!






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      Gravitational Field, nearly exactly how we are measuring EM field currently. LIGO proved it can be done for large object in 2017 when 2 black holes collided and generated gravitational waves.



      Starship in the future should be in the scale of million - trillion tonnes and moving at at least 10-20% speed of light, this would make considerable 'huge' amount of gravitational waves if moving 'close' together (by close I mean a few thousands kilometers). Heck we can measure gravitational waves emitted by black holes light years away now, absolutely we can do that for smaller objects within a few thousands kilometers in 200-300 years, especially if that object moves close to speed of light since it generates more identifiable ripples.



      I'm pretty sure we can work the math out to the exact dimensions of LIGO-like version needed to do this, but it would be terrifyingly difficult for people like us. I have strong background in electric engineering and still cannot grasp most part of it.






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        A patient passive approach could work. Observe ship apparent size and structure (visual angle) relative to your ship. Use an optical distance range finder. Integrate the number of naturally present cosmic rays passing through the other ship into your ship in order to passively estimate density - The ice cube observatory uses similar methods and works for space ships up to almost the thickness of Earth. Get an estimate of the other ships surface area & unseen sides by capacitance (just measure your own ships capacitance, deviation from typical solo deep space value indicates parallel capacitance of the nearby ship). Calculate surface to volume ratio and add density estimate from cosmic ray result for an estimate of mass that improves with more cosmic ray integrations.






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          Less than a hundreds years ago, we didn't have any application for electromagnetic waves, nor didn't know how to sense it. Now we can detect gravitational waves (well, only the strong). In future, we may have miniaturized sensitive technology to measure the disturbance in space-time.
          Who knows, may be we can sense the mass of the ship by measuring the turbulence it causes in the space-time.






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          • $begingroup$
            who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
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            – user6760
            14 hours ago






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            Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
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            – L.Dutch♦
            14 hours ago










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            This (handwavium waves) is the One True Answer.
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            – RonJohn
            13 hours ago



















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          You could ask them.



          Sure, this wont work in every situation. But if they cooperate, it's the best way. Your communications range is probably further than your sensor range, and you'll get the most accurate possible answer. Their computer will have to have the exact mass measurement at all times.






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            0












            $begingroup$

            Equipment that can survey the gravitational potential on the order of microgals is quite common today in geological industry and academia, known as gravimetry.



            The machines used as instrumentation, gravimeters, are quite interesting, but ultimately they are able to derive densities by way of directly measuring differing gravitational acceleration at many points. These have even been used to probe non-geological manmade-scale objects e.g. when French scientists surveyed the Cheops pyramid for unknown chambers.



            A tech advanced gravimeter (perhaps using an array of atom chip nano gravimeters) paired with a good gravimetric map of the navigation area should allow measurement of the mass of an anomalous body. With enough resolution you could even possibly map the density distribution of the vessel and track masses moving on the interior.






            share|improve this answer










            New contributor




            joshperry is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.






            $endgroup$













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              13 Answers
              13






              active

              oldest

              votes








              13 Answers
              13






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes









              33












              $begingroup$

              A few options ordered from "difficult but can be done at any time" to "easy, but requires an opportunity".



              Measure the gravitational lensing effect of the ship



              Every mass in the universe bends the space around it. This can be observed because stars behind the object appear displaced. This is how current day astronomers estimate the masses of astronomic objects (planets, stars, galaxies...). With access to much more precise instruments it might be possible to use the same principle for much smaller masses.



              If you are able to measure gravitational lensing around a regular sized space ship with current day technology, you know you are dealing with something with a really, really extreme density (neutron-star level)... or with something which uses artificial gravity technology. Anyway, it's definitely something based on technology far beyond anything you could comprehend. Proceed with caution!



              Measure the effect of its gravity on nearby objects



              If your instruments are not precise enough to measure its effect on light, you might still be able to measure its effect on dust clouds, micro-asteroids, space junk and other small objects when they get very close to the ship.



              But again, if they use artificial gravity technology, then that might screw up your measurement. Also check if the objects you measure contain any magnetic materials. If the ship generates a magnetic field for some reason (which can be an unintentional by-product of all kinds of devices), then that might also affect nearby objects.



              Measure its exhaust and the corresponding acceleration



              I would like to expand on point 3 of the answer by Darth Donut. If the engines of the ship work according to Newtons 3rd law of motion (which is the only way space propulsion can work according to our current understanding of physics), the kinetic force of the exhaust is exactly the same as the kinetic force applied to the ship. So when you observe the ship while it performs an acceleration burn, you can observe how much exhaust mass it expels per second and with what velocity. Multiply the two and you have its engine thrust. Divide the thrust by the acceleration of the ship you observe, and you have the mass of the ship.



              Measure how it behaves when hit by another object



              The ship is too light to cause any observable gravity effects and doesn't feel like performing any maneuvers right now? There is another way to apply Newton's laws to examine its mass. Wait until it gets hit by a micrometeroid. Measure the mass and acceleration of the meteroid and see how much the ship's velocity changes when it gets hit. When no meteroids are around, you could of course launch a known mass with a known acceleration at the ship yourself. But that might be perceived as impolite.






              share|improve this answer











              $endgroup$









              • 21




                $begingroup$
                "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
                $endgroup$
                – DarthDonut
                20 hours ago






              • 14




                $begingroup$
                "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
                $endgroup$
                – Kepotx
                19 hours ago






              • 3




                $begingroup$
                How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
                $endgroup$
                – Nuclear Wang
                16 hours ago






              • 2




                $begingroup$
                @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
                $endgroup$
                – Philipp
                16 hours ago






              • 3




                $begingroup$
                @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
                $endgroup$
                – Brilliand
                7 hours ago
















              33












              $begingroup$

              A few options ordered from "difficult but can be done at any time" to "easy, but requires an opportunity".



              Measure the gravitational lensing effect of the ship



              Every mass in the universe bends the space around it. This can be observed because stars behind the object appear displaced. This is how current day astronomers estimate the masses of astronomic objects (planets, stars, galaxies...). With access to much more precise instruments it might be possible to use the same principle for much smaller masses.



              If you are able to measure gravitational lensing around a regular sized space ship with current day technology, you know you are dealing with something with a really, really extreme density (neutron-star level)... or with something which uses artificial gravity technology. Anyway, it's definitely something based on technology far beyond anything you could comprehend. Proceed with caution!



              Measure the effect of its gravity on nearby objects



              If your instruments are not precise enough to measure its effect on light, you might still be able to measure its effect on dust clouds, micro-asteroids, space junk and other small objects when they get very close to the ship.



              But again, if they use artificial gravity technology, then that might screw up your measurement. Also check if the objects you measure contain any magnetic materials. If the ship generates a magnetic field for some reason (which can be an unintentional by-product of all kinds of devices), then that might also affect nearby objects.



              Measure its exhaust and the corresponding acceleration



              I would like to expand on point 3 of the answer by Darth Donut. If the engines of the ship work according to Newtons 3rd law of motion (which is the only way space propulsion can work according to our current understanding of physics), the kinetic force of the exhaust is exactly the same as the kinetic force applied to the ship. So when you observe the ship while it performs an acceleration burn, you can observe how much exhaust mass it expels per second and with what velocity. Multiply the two and you have its engine thrust. Divide the thrust by the acceleration of the ship you observe, and you have the mass of the ship.



              Measure how it behaves when hit by another object



              The ship is too light to cause any observable gravity effects and doesn't feel like performing any maneuvers right now? There is another way to apply Newton's laws to examine its mass. Wait until it gets hit by a micrometeroid. Measure the mass and acceleration of the meteroid and see how much the ship's velocity changes when it gets hit. When no meteroids are around, you could of course launch a known mass with a known acceleration at the ship yourself. But that might be perceived as impolite.






              share|improve this answer











              $endgroup$









              • 21




                $begingroup$
                "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
                $endgroup$
                – DarthDonut
                20 hours ago






              • 14




                $begingroup$
                "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
                $endgroup$
                – Kepotx
                19 hours ago






              • 3




                $begingroup$
                How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
                $endgroup$
                – Nuclear Wang
                16 hours ago






              • 2




                $begingroup$
                @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
                $endgroup$
                – Philipp
                16 hours ago






              • 3




                $begingroup$
                @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
                $endgroup$
                – Brilliand
                7 hours ago














              33












              33








              33





              $begingroup$

              A few options ordered from "difficult but can be done at any time" to "easy, but requires an opportunity".



              Measure the gravitational lensing effect of the ship



              Every mass in the universe bends the space around it. This can be observed because stars behind the object appear displaced. This is how current day astronomers estimate the masses of astronomic objects (planets, stars, galaxies...). With access to much more precise instruments it might be possible to use the same principle for much smaller masses.



              If you are able to measure gravitational lensing around a regular sized space ship with current day technology, you know you are dealing with something with a really, really extreme density (neutron-star level)... or with something which uses artificial gravity technology. Anyway, it's definitely something based on technology far beyond anything you could comprehend. Proceed with caution!



              Measure the effect of its gravity on nearby objects



              If your instruments are not precise enough to measure its effect on light, you might still be able to measure its effect on dust clouds, micro-asteroids, space junk and other small objects when they get very close to the ship.



              But again, if they use artificial gravity technology, then that might screw up your measurement. Also check if the objects you measure contain any magnetic materials. If the ship generates a magnetic field for some reason (which can be an unintentional by-product of all kinds of devices), then that might also affect nearby objects.



              Measure its exhaust and the corresponding acceleration



              I would like to expand on point 3 of the answer by Darth Donut. If the engines of the ship work according to Newtons 3rd law of motion (which is the only way space propulsion can work according to our current understanding of physics), the kinetic force of the exhaust is exactly the same as the kinetic force applied to the ship. So when you observe the ship while it performs an acceleration burn, you can observe how much exhaust mass it expels per second and with what velocity. Multiply the two and you have its engine thrust. Divide the thrust by the acceleration of the ship you observe, and you have the mass of the ship.



              Measure how it behaves when hit by another object



              The ship is too light to cause any observable gravity effects and doesn't feel like performing any maneuvers right now? There is another way to apply Newton's laws to examine its mass. Wait until it gets hit by a micrometeroid. Measure the mass and acceleration of the meteroid and see how much the ship's velocity changes when it gets hit. When no meteroids are around, you could of course launch a known mass with a known acceleration at the ship yourself. But that might be perceived as impolite.






              share|improve this answer











              $endgroup$



              A few options ordered from "difficult but can be done at any time" to "easy, but requires an opportunity".



              Measure the gravitational lensing effect of the ship



              Every mass in the universe bends the space around it. This can be observed because stars behind the object appear displaced. This is how current day astronomers estimate the masses of astronomic objects (planets, stars, galaxies...). With access to much more precise instruments it might be possible to use the same principle for much smaller masses.



              If you are able to measure gravitational lensing around a regular sized space ship with current day technology, you know you are dealing with something with a really, really extreme density (neutron-star level)... or with something which uses artificial gravity technology. Anyway, it's definitely something based on technology far beyond anything you could comprehend. Proceed with caution!



              Measure the effect of its gravity on nearby objects



              If your instruments are not precise enough to measure its effect on light, you might still be able to measure its effect on dust clouds, micro-asteroids, space junk and other small objects when they get very close to the ship.



              But again, if they use artificial gravity technology, then that might screw up your measurement. Also check if the objects you measure contain any magnetic materials. If the ship generates a magnetic field for some reason (which can be an unintentional by-product of all kinds of devices), then that might also affect nearby objects.



              Measure its exhaust and the corresponding acceleration



              I would like to expand on point 3 of the answer by Darth Donut. If the engines of the ship work according to Newtons 3rd law of motion (which is the only way space propulsion can work according to our current understanding of physics), the kinetic force of the exhaust is exactly the same as the kinetic force applied to the ship. So when you observe the ship while it performs an acceleration burn, you can observe how much exhaust mass it expels per second and with what velocity. Multiply the two and you have its engine thrust. Divide the thrust by the acceleration of the ship you observe, and you have the mass of the ship.



              Measure how it behaves when hit by another object



              The ship is too light to cause any observable gravity effects and doesn't feel like performing any maneuvers right now? There is another way to apply Newton's laws to examine its mass. Wait until it gets hit by a micrometeroid. Measure the mass and acceleration of the meteroid and see how much the ship's velocity changes when it gets hit. When no meteroids are around, you could of course launch a known mass with a known acceleration at the ship yourself. But that might be perceived as impolite.







              share|improve this answer














              share|improve this answer



              share|improve this answer








              edited 15 hours ago

























              answered 20 hours ago









              PhilippPhilipp

              31k1264118




              31k1264118








              • 21




                $begingroup$
                "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
                $endgroup$
                – DarthDonut
                20 hours ago






              • 14




                $begingroup$
                "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
                $endgroup$
                – Kepotx
                19 hours ago






              • 3




                $begingroup$
                How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
                $endgroup$
                – Nuclear Wang
                16 hours ago






              • 2




                $begingroup$
                @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
                $endgroup$
                – Philipp
                16 hours ago






              • 3




                $begingroup$
                @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
                $endgroup$
                – Brilliand
                7 hours ago














              • 21




                $begingroup$
                "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
                $endgroup$
                – DarthDonut
                20 hours ago






              • 14




                $begingroup$
                "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
                $endgroup$
                – Kepotx
                19 hours ago






              • 3




                $begingroup$
                How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
                $endgroup$
                – Nuclear Wang
                16 hours ago






              • 2




                $begingroup$
                @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
                $endgroup$
                – Philipp
                16 hours ago






              • 3




                $begingroup$
                @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
                $endgroup$
                – Brilliand
                7 hours ago








              21




              21




              $begingroup$
              "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
              $endgroup$
              – DarthDonut
              20 hours ago




              $begingroup$
              "But that might be perceived as impolite." - Might? I can only imagine: "Sir, Contact 47855-b has shot a small metal pellet at us! Reporting minor hull damages!" "Buggers, RETURN FIRE!" :)
              $endgroup$
              – DarthDonut
              20 hours ago




              14




              14




              $begingroup$
              "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
              $endgroup$
              – Kepotx
              19 hours ago




              $begingroup$
              "well, i guess they also want to know our ship mass by sending an object, but why they did this with several missiles?"
              $endgroup$
              – Kepotx
              19 hours ago




              3




              3




              $begingroup$
              How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
              $endgroup$
              – Nuclear Wang
              16 hours ago




              $begingroup$
              How do you measure the mass of the exhaust? I'd imagine that if you can do that by simple observation, you'd be able to just measure the mass of the ship itself.
              $endgroup$
              – Nuclear Wang
              16 hours ago




              2




              2




              $begingroup$
              @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
              $endgroup$
              – Philipp
              16 hours ago




              $begingroup$
              @NuclearWang The exhaust should be pretty easy to observe visually. With the ship you won't know what it hides beneath the hull.
              $endgroup$
              – Philipp
              16 hours ago




              3




              3




              $begingroup$
              @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
              $endgroup$
              – Brilliand
              7 hours ago




              $begingroup$
              @p.s.w.g That would be just as likely to be perceived as hostile as a bullet.
              $endgroup$
              – Brilliand
              7 hours ago











              21












              $begingroup$

              Here are a few ideas I got:



              1. Look up the ship type:

              As long as this ship you are seeing is not made by a to date unknown civilication, your databases should be able to identify the ship type, and show you some basic information for that.



              2. Estimate by size:

              As long as you can measure the distance, you can measure the size of such a ship. Now, your engineers will have an estimate for how much space is taken up by machinery, how much mass is used for the hull, how much space is needed for crew and so on. They know what materials are used commonly, and by multiplying the estimated volume with an average density you can estimate the mass of the ship. It is not a precise estimate, but your engineers should be pretty near to the exact value.



              3. Measure the acceleration and energy output of the engines:

              Every engine known to us emits radiation in some form due to conversion losses. As long as you can measure the acceleration of such a ship, the radiation of the engines and can identify the type of engine, you should be able to get a good estimate how much energy is used to power the engine, how much force the engines generate and in turn how much mass the ship has.



              Everything you need for the above methods are good optical sensors and radiation sensors.






              share|improve this answer









              $endgroup$









              • 1




                $begingroup$
                good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
                $endgroup$
                – Kepotx
                20 hours ago






              • 1




                $begingroup$
                wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
                $endgroup$
                – Kepotx
                20 hours ago






              • 3




                $begingroup$
                @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
                $endgroup$
                – DarthDonut
                20 hours ago








              • 1




                $begingroup$
                By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
                $endgroup$
                – Kepotx
                19 hours ago






              • 1




                $begingroup$
                Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
                $endgroup$
                – Separatrix
                18 hours ago
















              21












              $begingroup$

              Here are a few ideas I got:



              1. Look up the ship type:

              As long as this ship you are seeing is not made by a to date unknown civilication, your databases should be able to identify the ship type, and show you some basic information for that.



              2. Estimate by size:

              As long as you can measure the distance, you can measure the size of such a ship. Now, your engineers will have an estimate for how much space is taken up by machinery, how much mass is used for the hull, how much space is needed for crew and so on. They know what materials are used commonly, and by multiplying the estimated volume with an average density you can estimate the mass of the ship. It is not a precise estimate, but your engineers should be pretty near to the exact value.



              3. Measure the acceleration and energy output of the engines:

              Every engine known to us emits radiation in some form due to conversion losses. As long as you can measure the acceleration of such a ship, the radiation of the engines and can identify the type of engine, you should be able to get a good estimate how much energy is used to power the engine, how much force the engines generate and in turn how much mass the ship has.



              Everything you need for the above methods are good optical sensors and radiation sensors.






              share|improve this answer









              $endgroup$









              • 1




                $begingroup$
                good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
                $endgroup$
                – Kepotx
                20 hours ago






              • 1




                $begingroup$
                wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
                $endgroup$
                – Kepotx
                20 hours ago






              • 3




                $begingroup$
                @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
                $endgroup$
                – DarthDonut
                20 hours ago








              • 1




                $begingroup$
                By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
                $endgroup$
                – Kepotx
                19 hours ago






              • 1




                $begingroup$
                Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
                $endgroup$
                – Separatrix
                18 hours ago














              21












              21








              21





              $begingroup$

              Here are a few ideas I got:



              1. Look up the ship type:

              As long as this ship you are seeing is not made by a to date unknown civilication, your databases should be able to identify the ship type, and show you some basic information for that.



              2. Estimate by size:

              As long as you can measure the distance, you can measure the size of such a ship. Now, your engineers will have an estimate for how much space is taken up by machinery, how much mass is used for the hull, how much space is needed for crew and so on. They know what materials are used commonly, and by multiplying the estimated volume with an average density you can estimate the mass of the ship. It is not a precise estimate, but your engineers should be pretty near to the exact value.



              3. Measure the acceleration and energy output of the engines:

              Every engine known to us emits radiation in some form due to conversion losses. As long as you can measure the acceleration of such a ship, the radiation of the engines and can identify the type of engine, you should be able to get a good estimate how much energy is used to power the engine, how much force the engines generate and in turn how much mass the ship has.



              Everything you need for the above methods are good optical sensors and radiation sensors.






              share|improve this answer









              $endgroup$



              Here are a few ideas I got:



              1. Look up the ship type:

              As long as this ship you are seeing is not made by a to date unknown civilication, your databases should be able to identify the ship type, and show you some basic information for that.



              2. Estimate by size:

              As long as you can measure the distance, you can measure the size of such a ship. Now, your engineers will have an estimate for how much space is taken up by machinery, how much mass is used for the hull, how much space is needed for crew and so on. They know what materials are used commonly, and by multiplying the estimated volume with an average density you can estimate the mass of the ship. It is not a precise estimate, but your engineers should be pretty near to the exact value.



              3. Measure the acceleration and energy output of the engines:

              Every engine known to us emits radiation in some form due to conversion losses. As long as you can measure the acceleration of such a ship, the radiation of the engines and can identify the type of engine, you should be able to get a good estimate how much energy is used to power the engine, how much force the engines generate and in turn how much mass the ship has.



              Everything you need for the above methods are good optical sensors and radiation sensors.







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered 20 hours ago









              DarthDonutDarthDonut

              2,027214




              2,027214








              • 1




                $begingroup$
                good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
                $endgroup$
                – Kepotx
                20 hours ago






              • 1




                $begingroup$
                wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
                $endgroup$
                – Kepotx
                20 hours ago






              • 3




                $begingroup$
                @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
                $endgroup$
                – DarthDonut
                20 hours ago








              • 1




                $begingroup$
                By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
                $endgroup$
                – Kepotx
                19 hours ago






              • 1




                $begingroup$
                Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
                $endgroup$
                – Separatrix
                18 hours ago














              • 1




                $begingroup$
                good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
                $endgroup$
                – Kepotx
                20 hours ago






              • 1




                $begingroup$
                wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
                $endgroup$
                – Kepotx
                20 hours ago






              • 3




                $begingroup$
                @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
                $endgroup$
                – DarthDonut
                20 hours ago








              • 1




                $begingroup$
                By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
                $endgroup$
                – Kepotx
                19 hours ago






              • 1




                $begingroup$
                Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
                $endgroup$
                – Separatrix
                18 hours ago








              1




              1




              $begingroup$
              good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
              $endgroup$
              – Kepotx
              20 hours ago




              $begingroup$
              good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board.
              $endgroup$
              – Kepotx
              20 hours ago




              1




              1




              $begingroup$
              wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
              $endgroup$
              – Kepotx
              20 hours ago




              $begingroup$
              wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed)
              $endgroup$
              – Kepotx
              20 hours ago




              3




              3




              $begingroup$
              @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
              $endgroup$
              – DarthDonut
              20 hours ago






              $begingroup$
              @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses.
              $endgroup$
              – DarthDonut
              20 hours ago






              1




              1




              $begingroup$
              By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
              $endgroup$
              – Kepotx
              19 hours ago




              $begingroup$
              By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible.
              $endgroup$
              – Kepotx
              19 hours ago




              1




              1




              $begingroup$
              Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
              $endgroup$
              – Separatrix
              18 hours ago




              $begingroup$
              Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running.
              $endgroup$
              – Separatrix
              18 hours ago











              9












              $begingroup$

              The vacuum of space act as a dielectric.



              If you are close enough, provide a net electric charge to your own ship. This will induce a charge also on the probed ship, and will trigger an electrostatic attraction between the two.



              Measure your velocity with respect to background and your velocity with respect to the probed ship.



              Since you know the charge involved and you can determine the resulting force exerted on the probed ship. The resulting force will change your velocity and the one of the probed ship. You know your mass and your velocity both with respect to background and to probed ship, the only unknown parameter is the probed ship mass.






              share|improve this answer









              $endgroup$









              • 1




                $begingroup$
                What If the're also doing the same thing? It could affect the measurement...
                $endgroup$
                – user000001
                12 hours ago








              • 1




                $begingroup$
                How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
                $endgroup$
                – WGroleau
                9 hours ago


















              9












              $begingroup$

              The vacuum of space act as a dielectric.



              If you are close enough, provide a net electric charge to your own ship. This will induce a charge also on the probed ship, and will trigger an electrostatic attraction between the two.



              Measure your velocity with respect to background and your velocity with respect to the probed ship.



              Since you know the charge involved and you can determine the resulting force exerted on the probed ship. The resulting force will change your velocity and the one of the probed ship. You know your mass and your velocity both with respect to background and to probed ship, the only unknown parameter is the probed ship mass.






              share|improve this answer









              $endgroup$









              • 1




                $begingroup$
                What If the're also doing the same thing? It could affect the measurement...
                $endgroup$
                – user000001
                12 hours ago








              • 1




                $begingroup$
                How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
                $endgroup$
                – WGroleau
                9 hours ago
















              9












              9








              9





              $begingroup$

              The vacuum of space act as a dielectric.



              If you are close enough, provide a net electric charge to your own ship. This will induce a charge also on the probed ship, and will trigger an electrostatic attraction between the two.



              Measure your velocity with respect to background and your velocity with respect to the probed ship.



              Since you know the charge involved and you can determine the resulting force exerted on the probed ship. The resulting force will change your velocity and the one of the probed ship. You know your mass and your velocity both with respect to background and to probed ship, the only unknown parameter is the probed ship mass.






              share|improve this answer









              $endgroup$



              The vacuum of space act as a dielectric.



              If you are close enough, provide a net electric charge to your own ship. This will induce a charge also on the probed ship, and will trigger an electrostatic attraction between the two.



              Measure your velocity with respect to background and your velocity with respect to the probed ship.



              Since you know the charge involved and you can determine the resulting force exerted on the probed ship. The resulting force will change your velocity and the one of the probed ship. You know your mass and your velocity both with respect to background and to probed ship, the only unknown parameter is the probed ship mass.







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered 19 hours ago









              L.Dutch♦L.Dutch

              86.3k29201421




              86.3k29201421








              • 1




                $begingroup$
                What If the're also doing the same thing? It could affect the measurement...
                $endgroup$
                – user000001
                12 hours ago








              • 1




                $begingroup$
                How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
                $endgroup$
                – WGroleau
                9 hours ago
















              • 1




                $begingroup$
                What If the're also doing the same thing? It could affect the measurement...
                $endgroup$
                – user000001
                12 hours ago








              • 1




                $begingroup$
                How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
                $endgroup$
                – WGroleau
                9 hours ago










              1




              1




              $begingroup$
              What If the're also doing the same thing? It could affect the measurement...
              $endgroup$
              – user000001
              12 hours ago






              $begingroup$
              What If the're also doing the same thing? It could affect the measurement...
              $endgroup$
              – user000001
              12 hours ago






              1




              1




              $begingroup$
              How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
              $endgroup$
              – WGroleau
              9 hours ago






              $begingroup$
              How are you going to charge your ship? Spew a kilocoulomb of electrons into space? How often can you do that before people& things not “earthed” to the ship get electrostatic damage?
              $endgroup$
              – WGroleau
              9 hours ago













              6












              $begingroup$

              Probe indirectly



              Launch a small probe of precisely known mass so that it passes at a known distance from the ship. The probe might be as opaque and undetectable as could be. At a predetermined moment the probe shoots a low-power laser signal to the mothership, allowing its position to be precisely determined. From there, you can work back the deflection on the trajectory caused by the gravitational mass of the unknown ship.



              Probe (almost) directly



              Send two probes at different distances from the unknown ship, depending on how sensitive their gravitational sensors are. Measure acceleration on both probes. These will be caused by all nearby masses (the mothership included), but using two probes, the residual that has quadratic dependency on the unknown ship's distance once the other masses are ruled out will give the unknown ship's mass.



              For example if all other masses are sufficiently far away, the distance between them and probes P and Q may be taken as constant, so the differential will be zero. The acceleration on probe P will then be given by G(M/a^2 - X/(b+d)^2) while that on probe Q by G(M/(a+d)^2 - X/b^2), with M and X the masses of the mothership and the unknown's, a and b the distances of the first probe from the mothership M and the unknown, and d the distance between the probes:



                   M            P         Q                                        X
              
     |--- a ------|--- d ---|--------------------- b ----------------|


              Assuming b, especially, is known with sufficient accuracy (phased laser ranging, maybe?) and accelerometers of sufficient precision are available, the two probes could even be mounted on a fixed "antenna" (it is not necessary for M, P, Q and X to be aligned on a line, but this simplifies things).






              share|improve this answer









              $endgroup$


















                6












                $begingroup$

                Probe indirectly



                Launch a small probe of precisely known mass so that it passes at a known distance from the ship. The probe might be as opaque and undetectable as could be. At a predetermined moment the probe shoots a low-power laser signal to the mothership, allowing its position to be precisely determined. From there, you can work back the deflection on the trajectory caused by the gravitational mass of the unknown ship.



                Probe (almost) directly



                Send two probes at different distances from the unknown ship, depending on how sensitive their gravitational sensors are. Measure acceleration on both probes. These will be caused by all nearby masses (the mothership included), but using two probes, the residual that has quadratic dependency on the unknown ship's distance once the other masses are ruled out will give the unknown ship's mass.



                For example if all other masses are sufficiently far away, the distance between them and probes P and Q may be taken as constant, so the differential will be zero. The acceleration on probe P will then be given by G(M/a^2 - X/(b+d)^2) while that on probe Q by G(M/(a+d)^2 - X/b^2), with M and X the masses of the mothership and the unknown's, a and b the distances of the first probe from the mothership M and the unknown, and d the distance between the probes:



                     M            P         Q                                        X
                
     |--- a ------|--- d ---|--------------------- b ----------------|


                Assuming b, especially, is known with sufficient accuracy (phased laser ranging, maybe?) and accelerometers of sufficient precision are available, the two probes could even be mounted on a fixed "antenna" (it is not necessary for M, P, Q and X to be aligned on a line, but this simplifies things).






                share|improve this answer









                $endgroup$
















                  6












                  6








                  6





                  $begingroup$

                  Probe indirectly



                  Launch a small probe of precisely known mass so that it passes at a known distance from the ship. The probe might be as opaque and undetectable as could be. At a predetermined moment the probe shoots a low-power laser signal to the mothership, allowing its position to be precisely determined. From there, you can work back the deflection on the trajectory caused by the gravitational mass of the unknown ship.



                  Probe (almost) directly



                  Send two probes at different distances from the unknown ship, depending on how sensitive their gravitational sensors are. Measure acceleration on both probes. These will be caused by all nearby masses (the mothership included), but using two probes, the residual that has quadratic dependency on the unknown ship's distance once the other masses are ruled out will give the unknown ship's mass.



                  For example if all other masses are sufficiently far away, the distance between them and probes P and Q may be taken as constant, so the differential will be zero. The acceleration on probe P will then be given by G(M/a^2 - X/(b+d)^2) while that on probe Q by G(M/(a+d)^2 - X/b^2), with M and X the masses of the mothership and the unknown's, a and b the distances of the first probe from the mothership M and the unknown, and d the distance between the probes:



                       M            P         Q                                        X
                  
     |--- a ------|--- d ---|--------------------- b ----------------|


                  Assuming b, especially, is known with sufficient accuracy (phased laser ranging, maybe?) and accelerometers of sufficient precision are available, the two probes could even be mounted on a fixed "antenna" (it is not necessary for M, P, Q and X to be aligned on a line, but this simplifies things).






                  share|improve this answer









                  $endgroup$



                  Probe indirectly



                  Launch a small probe of precisely known mass so that it passes at a known distance from the ship. The probe might be as opaque and undetectable as could be. At a predetermined moment the probe shoots a low-power laser signal to the mothership, allowing its position to be precisely determined. From there, you can work back the deflection on the trajectory caused by the gravitational mass of the unknown ship.



                  Probe (almost) directly



                  Send two probes at different distances from the unknown ship, depending on how sensitive their gravitational sensors are. Measure acceleration on both probes. These will be caused by all nearby masses (the mothership included), but using two probes, the residual that has quadratic dependency on the unknown ship's distance once the other masses are ruled out will give the unknown ship's mass.



                  For example if all other masses are sufficiently far away, the distance between them and probes P and Q may be taken as constant, so the differential will be zero. The acceleration on probe P will then be given by G(M/a^2 - X/(b+d)^2) while that on probe Q by G(M/(a+d)^2 - X/b^2), with M and X the masses of the mothership and the unknown's, a and b the distances of the first probe from the mothership M and the unknown, and d the distance between the probes:



                       M            P         Q                                        X
                  
     |--- a ------|--- d ---|--------------------- b ----------------|


                  Assuming b, especially, is known with sufficient accuracy (phased laser ranging, maybe?) and accelerometers of sufficient precision are available, the two probes could even be mounted on a fixed "antenna" (it is not necessary for M, P, Q and X to be aligned on a line, but this simplifies things).







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 16 hours ago









                  LSerniLSerni

                  28.1k24989




                  28.1k24989























                      4












                      $begingroup$

                      Shoot them with a powerful laser and see how much the momentum of their ship changes.



                      You didn't mention anything about leaving the ship intact.






                      share|improve this answer









                      $endgroup$









                      • 3




                        $begingroup$
                        Sounds good until you find out they have a more powerful laser.
                        $endgroup$
                        – prl
                        11 hours ago






                      • 1




                        $begingroup$
                        @prl "If you must swing first, swing hard.. and connect."
                        $endgroup$
                        – Cort Ammon
                        1 hour ago
















                      4












                      $begingroup$

                      Shoot them with a powerful laser and see how much the momentum of their ship changes.



                      You didn't mention anything about leaving the ship intact.






                      share|improve this answer









                      $endgroup$









                      • 3




                        $begingroup$
                        Sounds good until you find out they have a more powerful laser.
                        $endgroup$
                        – prl
                        11 hours ago






                      • 1




                        $begingroup$
                        @prl "If you must swing first, swing hard.. and connect."
                        $endgroup$
                        – Cort Ammon
                        1 hour ago














                      4












                      4








                      4





                      $begingroup$

                      Shoot them with a powerful laser and see how much the momentum of their ship changes.



                      You didn't mention anything about leaving the ship intact.






                      share|improve this answer









                      $endgroup$



                      Shoot them with a powerful laser and see how much the momentum of their ship changes.



                      You didn't mention anything about leaving the ship intact.







                      share|improve this answer












                      share|improve this answer



                      share|improve this answer










                      answered 15 hours ago









                      RenanRenan

                      49.4k13115249




                      49.4k13115249








                      • 3




                        $begingroup$
                        Sounds good until you find out they have a more powerful laser.
                        $endgroup$
                        – prl
                        11 hours ago






                      • 1




                        $begingroup$
                        @prl "If you must swing first, swing hard.. and connect."
                        $endgroup$
                        – Cort Ammon
                        1 hour ago














                      • 3




                        $begingroup$
                        Sounds good until you find out they have a more powerful laser.
                        $endgroup$
                        – prl
                        11 hours ago






                      • 1




                        $begingroup$
                        @prl "If you must swing first, swing hard.. and connect."
                        $endgroup$
                        – Cort Ammon
                        1 hour ago








                      3




                      3




                      $begingroup$
                      Sounds good until you find out they have a more powerful laser.
                      $endgroup$
                      – prl
                      11 hours ago




                      $begingroup$
                      Sounds good until you find out they have a more powerful laser.
                      $endgroup$
                      – prl
                      11 hours ago




                      1




                      1




                      $begingroup$
                      @prl "If you must swing first, swing hard.. and connect."
                      $endgroup$
                      – Cort Ammon
                      1 hour ago




                      $begingroup$
                      @prl "If you must swing first, swing hard.. and connect."
                      $endgroup$
                      – Cort Ammon
                      1 hour ago











                      3












                      $begingroup$

                      Shine a laser at it, and measure the (exceedingly slight) change in momentum.




                      Several years later, in 1922, physicist Arthur Compton performed an
                      experiment which led to the discovery of the Compton Effect. Proving
                      Einstein correct, Compton showed that photons indeed have momentum
                      which is transferrable to materials that have a mass. Compton was
                      awarded the 1927 Noble Prize in Physics for demonstrating that photons
                      can transfer their momentum to the electrons with which they collide
                      inside an atom.




                      I am, of course, assuming that by the time there are enough spaceships out there that one needs to worry about determining their mass, we will have the technology to be able to detect very minute changes in momentum that a laser beam would impart on a ship. Yes, I am aware that it would be easier to detect the change in momentum caused by a flea smacking into a super jumbo jet, but hey, we are talking about the future here.






                      share|improve this answer











                      $endgroup$









                      • 1




                        $begingroup$
                        It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
                        $endgroup$
                        – prl
                        11 hours ago










                      • $begingroup$
                        @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
                        $endgroup$
                        – Justin Thyme
                        5 hours ago
















                      3












                      $begingroup$

                      Shine a laser at it, and measure the (exceedingly slight) change in momentum.




                      Several years later, in 1922, physicist Arthur Compton performed an
                      experiment which led to the discovery of the Compton Effect. Proving
                      Einstein correct, Compton showed that photons indeed have momentum
                      which is transferrable to materials that have a mass. Compton was
                      awarded the 1927 Noble Prize in Physics for demonstrating that photons
                      can transfer their momentum to the electrons with which they collide
                      inside an atom.




                      I am, of course, assuming that by the time there are enough spaceships out there that one needs to worry about determining their mass, we will have the technology to be able to detect very minute changes in momentum that a laser beam would impart on a ship. Yes, I am aware that it would be easier to detect the change in momentum caused by a flea smacking into a super jumbo jet, but hey, we are talking about the future here.






                      share|improve this answer











                      $endgroup$









                      • 1




                        $begingroup$
                        It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
                        $endgroup$
                        – prl
                        11 hours ago










                      • $begingroup$
                        @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
                        $endgroup$
                        – Justin Thyme
                        5 hours ago














                      3












                      3








                      3





                      $begingroup$

                      Shine a laser at it, and measure the (exceedingly slight) change in momentum.




                      Several years later, in 1922, physicist Arthur Compton performed an
                      experiment which led to the discovery of the Compton Effect. Proving
                      Einstein correct, Compton showed that photons indeed have momentum
                      which is transferrable to materials that have a mass. Compton was
                      awarded the 1927 Noble Prize in Physics for demonstrating that photons
                      can transfer their momentum to the electrons with which they collide
                      inside an atom.




                      I am, of course, assuming that by the time there are enough spaceships out there that one needs to worry about determining their mass, we will have the technology to be able to detect very minute changes in momentum that a laser beam would impart on a ship. Yes, I am aware that it would be easier to detect the change in momentum caused by a flea smacking into a super jumbo jet, but hey, we are talking about the future here.






                      share|improve this answer











                      $endgroup$



                      Shine a laser at it, and measure the (exceedingly slight) change in momentum.




                      Several years later, in 1922, physicist Arthur Compton performed an
                      experiment which led to the discovery of the Compton Effect. Proving
                      Einstein correct, Compton showed that photons indeed have momentum
                      which is transferrable to materials that have a mass. Compton was
                      awarded the 1927 Noble Prize in Physics for demonstrating that photons
                      can transfer their momentum to the electrons with which they collide
                      inside an atom.




                      I am, of course, assuming that by the time there are enough spaceships out there that one needs to worry about determining their mass, we will have the technology to be able to detect very minute changes in momentum that a laser beam would impart on a ship. Yes, I am aware that it would be easier to detect the change in momentum caused by a flea smacking into a super jumbo jet, but hey, we are talking about the future here.







                      share|improve this answer














                      share|improve this answer



                      share|improve this answer








                      edited 14 hours ago

























                      answered 15 hours ago









                      Justin ThymeJustin Thyme

                      8,46311042




                      8,46311042








                      • 1




                        $begingroup$
                        It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
                        $endgroup$
                        – prl
                        11 hours ago










                      • $begingroup$
                        @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
                        $endgroup$
                        – Justin Thyme
                        5 hours ago














                      • 1




                        $begingroup$
                        It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
                        $endgroup$
                        – prl
                        11 hours ago










                      • $begingroup$
                        @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
                        $endgroup$
                        – Justin Thyme
                        5 hours ago








                      1




                      1




                      $begingroup$
                      It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
                      $endgroup$
                      – prl
                      11 hours ago




                      $begingroup$
                      It seems that people moving around inside the spaceship might have a bigger effect than the laser, making it hard to extract signal from noise.
                      $endgroup$
                      – prl
                      11 hours ago












                      $begingroup$
                      @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
                      $endgroup$
                      – Justin Thyme
                      5 hours ago




                      $begingroup$
                      @prl It would for sure require a lot of iterations to sort out noise from signal.. But apparently intelligence services were able to detect what was on the old CRT monitors by detecting the varying light levels in a room,ans the beam moved across the screen and satellite phones can filter out every signal BUT the one signal from the one phone across a huge section of the globe, through all of the electromagnetic noise. Fourier transforms, maybe?
                      $endgroup$
                      – Justin Thyme
                      5 hours ago











                      3












                      $begingroup$

                      Scan them. Fire a very large burst of neutrinos at them and measure how much gets reflected back. In general the more massive an object is the more return signal you will get. It works okay for an estimated order of magnitude.



                      Unlike other answers this probably won't be recognized as an act of violence, doesn't disturb their trajectory and gives you an answer near to light speeds.



                      Edit: Actually, I'm no physicist but I think you won't get neutrinos back, you might get electrons, but I'm just not knowledgeable enough to say for sure.






                      share|improve this answer








                      New contributor




                      JDrumm is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                      Check out our Code of Conduct.






                      $endgroup$













                      • $begingroup$
                        Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
                        $endgroup$
                        – Mark
                        9 hours ago
















                      3












                      $begingroup$

                      Scan them. Fire a very large burst of neutrinos at them and measure how much gets reflected back. In general the more massive an object is the more return signal you will get. It works okay for an estimated order of magnitude.



                      Unlike other answers this probably won't be recognized as an act of violence, doesn't disturb their trajectory and gives you an answer near to light speeds.



                      Edit: Actually, I'm no physicist but I think you won't get neutrinos back, you might get electrons, but I'm just not knowledgeable enough to say for sure.






                      share|improve this answer








                      New contributor




                      JDrumm is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                      Check out our Code of Conduct.






                      $endgroup$













                      • $begingroup$
                        Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
                        $endgroup$
                        – Mark
                        9 hours ago














                      3












                      3








                      3





                      $begingroup$

                      Scan them. Fire a very large burst of neutrinos at them and measure how much gets reflected back. In general the more massive an object is the more return signal you will get. It works okay for an estimated order of magnitude.



                      Unlike other answers this probably won't be recognized as an act of violence, doesn't disturb their trajectory and gives you an answer near to light speeds.



                      Edit: Actually, I'm no physicist but I think you won't get neutrinos back, you might get electrons, but I'm just not knowledgeable enough to say for sure.






                      share|improve this answer








                      New contributor




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                      $endgroup$



                      Scan them. Fire a very large burst of neutrinos at them and measure how much gets reflected back. In general the more massive an object is the more return signal you will get. It works okay for an estimated order of magnitude.



                      Unlike other answers this probably won't be recognized as an act of violence, doesn't disturb their trajectory and gives you an answer near to light speeds.



                      Edit: Actually, I'm no physicist but I think you won't get neutrinos back, you might get electrons, but I'm just not knowledgeable enough to say for sure.







                      share|improve this answer








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                      share|improve this answer



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                      answered 14 hours ago









                      JDrummJDrumm

                      411




                      411




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                      New contributor





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                      • $begingroup$
                        Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
                        $endgroup$
                        – Mark
                        9 hours ago


















                      • $begingroup$
                        Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
                        $endgroup$
                        – Mark
                        9 hours ago
















                      $begingroup$
                      Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
                      $endgroup$
                      – Mark
                      9 hours ago




                      $begingroup$
                      Where are you going to get the very large burst of neutrinos? Ordinary nuclear reactors and particle accelerators don't generate enough to be usable, and lighting someone up with a nuclear flashbulb might be mistaken for a hostile act.
                      $endgroup$
                      – Mark
                      9 hours ago











                      2












                      $begingroup$

                      In Civilized Areas, They will Tell You Automatically



                      Today, ships and aircraft have systems that self report their name, size, exact location, velocity, destination etc. For ships, this is AIS, and for aircraft it is ADS-B. The systems automatically squawk their info a regular intervals, so as soon as you are in receiving range you know what the contact picture is.



                      It is often required by the relevant authorities, as it significantly improves safety when everyone knows where everyone else is.



                      Otherwise, IR will give a Good Guess



                      All vessels will have a power source. This power source is going to have waste heat, which will radiate from the vessel evenly. (Unless the owner pumps air/fluids around to deliberately alter the heat transfer.) This waste heat will be subject to one over r squared losses. If you can determine a range, you can determine how much this blackbody radiation will have dropped off, and you can get an estimate of the size of the power source.



                      Power is going to be strongly related to vessel size and acceleration. The exact equation is probably going to be complex, but luckily the universe is full of vessels providing you with empirical data!






                      share|improve this answer









                      $endgroup$


















                        2












                        $begingroup$

                        In Civilized Areas, They will Tell You Automatically



                        Today, ships and aircraft have systems that self report their name, size, exact location, velocity, destination etc. For ships, this is AIS, and for aircraft it is ADS-B. The systems automatically squawk their info a regular intervals, so as soon as you are in receiving range you know what the contact picture is.



                        It is often required by the relevant authorities, as it significantly improves safety when everyone knows where everyone else is.



                        Otherwise, IR will give a Good Guess



                        All vessels will have a power source. This power source is going to have waste heat, which will radiate from the vessel evenly. (Unless the owner pumps air/fluids around to deliberately alter the heat transfer.) This waste heat will be subject to one over r squared losses. If you can determine a range, you can determine how much this blackbody radiation will have dropped off, and you can get an estimate of the size of the power source.



                        Power is going to be strongly related to vessel size and acceleration. The exact equation is probably going to be complex, but luckily the universe is full of vessels providing you with empirical data!






                        share|improve this answer









                        $endgroup$
















                          2












                          2








                          2





                          $begingroup$

                          In Civilized Areas, They will Tell You Automatically



                          Today, ships and aircraft have systems that self report their name, size, exact location, velocity, destination etc. For ships, this is AIS, and for aircraft it is ADS-B. The systems automatically squawk their info a regular intervals, so as soon as you are in receiving range you know what the contact picture is.



                          It is often required by the relevant authorities, as it significantly improves safety when everyone knows where everyone else is.



                          Otherwise, IR will give a Good Guess



                          All vessels will have a power source. This power source is going to have waste heat, which will radiate from the vessel evenly. (Unless the owner pumps air/fluids around to deliberately alter the heat transfer.) This waste heat will be subject to one over r squared losses. If you can determine a range, you can determine how much this blackbody radiation will have dropped off, and you can get an estimate of the size of the power source.



                          Power is going to be strongly related to vessel size and acceleration. The exact equation is probably going to be complex, but luckily the universe is full of vessels providing you with empirical data!






                          share|improve this answer









                          $endgroup$



                          In Civilized Areas, They will Tell You Automatically



                          Today, ships and aircraft have systems that self report their name, size, exact location, velocity, destination etc. For ships, this is AIS, and for aircraft it is ADS-B. The systems automatically squawk their info a regular intervals, so as soon as you are in receiving range you know what the contact picture is.



                          It is often required by the relevant authorities, as it significantly improves safety when everyone knows where everyone else is.



                          Otherwise, IR will give a Good Guess



                          All vessels will have a power source. This power source is going to have waste heat, which will radiate from the vessel evenly. (Unless the owner pumps air/fluids around to deliberately alter the heat transfer.) This waste heat will be subject to one over r squared losses. If you can determine a range, you can determine how much this blackbody radiation will have dropped off, and you can get an estimate of the size of the power source.



                          Power is going to be strongly related to vessel size and acceleration. The exact equation is probably going to be complex, but luckily the universe is full of vessels providing you with empirical data!







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 7 hours ago









                          codeMonkeycodeMonkey

                          2,934816




                          2,934816























                              1












                              $begingroup$

                              Gravitational Field, nearly exactly how we are measuring EM field currently. LIGO proved it can be done for large object in 2017 when 2 black holes collided and generated gravitational waves.



                              Starship in the future should be in the scale of million - trillion tonnes and moving at at least 10-20% speed of light, this would make considerable 'huge' amount of gravitational waves if moving 'close' together (by close I mean a few thousands kilometers). Heck we can measure gravitational waves emitted by black holes light years away now, absolutely we can do that for smaller objects within a few thousands kilometers in 200-300 years, especially if that object moves close to speed of light since it generates more identifiable ripples.



                              I'm pretty sure we can work the math out to the exact dimensions of LIGO-like version needed to do this, but it would be terrifyingly difficult for people like us. I have strong background in electric engineering and still cannot grasp most part of it.






                              share|improve this answer








                              New contributor




                              Ân Vương is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                              $endgroup$


















                                1












                                $begingroup$

                                Gravitational Field, nearly exactly how we are measuring EM field currently. LIGO proved it can be done for large object in 2017 when 2 black holes collided and generated gravitational waves.



                                Starship in the future should be in the scale of million - trillion tonnes and moving at at least 10-20% speed of light, this would make considerable 'huge' amount of gravitational waves if moving 'close' together (by close I mean a few thousands kilometers). Heck we can measure gravitational waves emitted by black holes light years away now, absolutely we can do that for smaller objects within a few thousands kilometers in 200-300 years, especially if that object moves close to speed of light since it generates more identifiable ripples.



                                I'm pretty sure we can work the math out to the exact dimensions of LIGO-like version needed to do this, but it would be terrifyingly difficult for people like us. I have strong background in electric engineering and still cannot grasp most part of it.






                                share|improve this answer








                                New contributor




                                Ân Vương is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                Check out our Code of Conduct.






                                $endgroup$
















                                  1












                                  1








                                  1





                                  $begingroup$

                                  Gravitational Field, nearly exactly how we are measuring EM field currently. LIGO proved it can be done for large object in 2017 when 2 black holes collided and generated gravitational waves.



                                  Starship in the future should be in the scale of million - trillion tonnes and moving at at least 10-20% speed of light, this would make considerable 'huge' amount of gravitational waves if moving 'close' together (by close I mean a few thousands kilometers). Heck we can measure gravitational waves emitted by black holes light years away now, absolutely we can do that for smaller objects within a few thousands kilometers in 200-300 years, especially if that object moves close to speed of light since it generates more identifiable ripples.



                                  I'm pretty sure we can work the math out to the exact dimensions of LIGO-like version needed to do this, but it would be terrifyingly difficult for people like us. I have strong background in electric engineering and still cannot grasp most part of it.






                                  share|improve this answer








                                  New contributor




                                  Ân Vương is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                  Check out our Code of Conduct.






                                  $endgroup$



                                  Gravitational Field, nearly exactly how we are measuring EM field currently. LIGO proved it can be done for large object in 2017 when 2 black holes collided and generated gravitational waves.



                                  Starship in the future should be in the scale of million - trillion tonnes and moving at at least 10-20% speed of light, this would make considerable 'huge' amount of gravitational waves if moving 'close' together (by close I mean a few thousands kilometers). Heck we can measure gravitational waves emitted by black holes light years away now, absolutely we can do that for smaller objects within a few thousands kilometers in 200-300 years, especially if that object moves close to speed of light since it generates more identifiable ripples.



                                  I'm pretty sure we can work the math out to the exact dimensions of LIGO-like version needed to do this, but it would be terrifyingly difficult for people like us. I have strong background in electric engineering and still cannot grasp most part of it.







                                  share|improve this answer








                                  New contributor




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                                  share|improve this answer



                                  share|improve this answer






                                  New contributor




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                                  answered 1 hour ago









                                  Ân VươngÂn Vương

                                  111




                                  111




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                                  New contributor





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                                      1












                                      $begingroup$

                                      A patient passive approach could work. Observe ship apparent size and structure (visual angle) relative to your ship. Use an optical distance range finder. Integrate the number of naturally present cosmic rays passing through the other ship into your ship in order to passively estimate density - The ice cube observatory uses similar methods and works for space ships up to almost the thickness of Earth. Get an estimate of the other ships surface area & unseen sides by capacitance (just measure your own ships capacitance, deviation from typical solo deep space value indicates parallel capacitance of the nearby ship). Calculate surface to volume ratio and add density estimate from cosmic ray result for an estimate of mass that improves with more cosmic ray integrations.






                                      share|improve this answer










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                                      $endgroup$


















                                        1












                                        $begingroup$

                                        A patient passive approach could work. Observe ship apparent size and structure (visual angle) relative to your ship. Use an optical distance range finder. Integrate the number of naturally present cosmic rays passing through the other ship into your ship in order to passively estimate density - The ice cube observatory uses similar methods and works for space ships up to almost the thickness of Earth. Get an estimate of the other ships surface area & unseen sides by capacitance (just measure your own ships capacitance, deviation from typical solo deep space value indicates parallel capacitance of the nearby ship). Calculate surface to volume ratio and add density estimate from cosmic ray result for an estimate of mass that improves with more cosmic ray integrations.






                                        share|improve this answer










                                        New contributor




                                        dusty is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                        Check out our Code of Conduct.






                                        $endgroup$
















                                          1












                                          1








                                          1





                                          $begingroup$

                                          A patient passive approach could work. Observe ship apparent size and structure (visual angle) relative to your ship. Use an optical distance range finder. Integrate the number of naturally present cosmic rays passing through the other ship into your ship in order to passively estimate density - The ice cube observatory uses similar methods and works for space ships up to almost the thickness of Earth. Get an estimate of the other ships surface area & unseen sides by capacitance (just measure your own ships capacitance, deviation from typical solo deep space value indicates parallel capacitance of the nearby ship). Calculate surface to volume ratio and add density estimate from cosmic ray result for an estimate of mass that improves with more cosmic ray integrations.






                                          share|improve this answer










                                          New contributor




                                          dusty is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                          Check out our Code of Conduct.






                                          $endgroup$



                                          A patient passive approach could work. Observe ship apparent size and structure (visual angle) relative to your ship. Use an optical distance range finder. Integrate the number of naturally present cosmic rays passing through the other ship into your ship in order to passively estimate density - The ice cube observatory uses similar methods and works for space ships up to almost the thickness of Earth. Get an estimate of the other ships surface area & unseen sides by capacitance (just measure your own ships capacitance, deviation from typical solo deep space value indicates parallel capacitance of the nearby ship). Calculate surface to volume ratio and add density estimate from cosmic ray result for an estimate of mass that improves with more cosmic ray integrations.







                                          share|improve this answer










                                          New contributor




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                                          share|improve this answer



                                          share|improve this answer








                                          edited 1 hour ago





















                                          New contributor




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                                          answered 1 hour ago









                                          dustydusty

                                          112




                                          112




                                          New contributor




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                                          New contributor





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                                          dusty is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                                              0












                                              $begingroup$

                                              Less than a hundreds years ago, we didn't have any application for electromagnetic waves, nor didn't know how to sense it. Now we can detect gravitational waves (well, only the strong). In future, we may have miniaturized sensitive technology to measure the disturbance in space-time.
                                              Who knows, may be we can sense the mass of the ship by measuring the turbulence it causes in the space-time.






                                              share|improve this answer








                                              New contributor




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                                              $endgroup$













                                              • $begingroup$
                                                who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                                                $endgroup$
                                                – user6760
                                                14 hours ago






                                              • 1




                                                $begingroup$
                                                Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
                                                $endgroup$
                                                – L.Dutch♦
                                                14 hours ago










                                              • $begingroup$
                                                This (handwavium waves) is the One True Answer.
                                                $endgroup$
                                                – RonJohn
                                                13 hours ago
















                                              0












                                              $begingroup$

                                              Less than a hundreds years ago, we didn't have any application for electromagnetic waves, nor didn't know how to sense it. Now we can detect gravitational waves (well, only the strong). In future, we may have miniaturized sensitive technology to measure the disturbance in space-time.
                                              Who knows, may be we can sense the mass of the ship by measuring the turbulence it causes in the space-time.






                                              share|improve this answer








                                              New contributor




                                              Thanushan is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                              Check out our Code of Conduct.






                                              $endgroup$













                                              • $begingroup$
                                                who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                                                $endgroup$
                                                – user6760
                                                14 hours ago






                                              • 1




                                                $begingroup$
                                                Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
                                                $endgroup$
                                                – L.Dutch♦
                                                14 hours ago










                                              • $begingroup$
                                                This (handwavium waves) is the One True Answer.
                                                $endgroup$
                                                – RonJohn
                                                13 hours ago














                                              0












                                              0








                                              0





                                              $begingroup$

                                              Less than a hundreds years ago, we didn't have any application for electromagnetic waves, nor didn't know how to sense it. Now we can detect gravitational waves (well, only the strong). In future, we may have miniaturized sensitive technology to measure the disturbance in space-time.
                                              Who knows, may be we can sense the mass of the ship by measuring the turbulence it causes in the space-time.






                                              share|improve this answer








                                              New contributor




                                              Thanushan is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                              Check out our Code of Conduct.






                                              $endgroup$



                                              Less than a hundreds years ago, we didn't have any application for electromagnetic waves, nor didn't know how to sense it. Now we can detect gravitational waves (well, only the strong). In future, we may have miniaturized sensitive technology to measure the disturbance in space-time.
                                              Who knows, may be we can sense the mass of the ship by measuring the turbulence it causes in the space-time.







                                              share|improve this answer








                                              New contributor




                                              Thanushan is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                                              share|improve this answer



                                              share|improve this answer






                                              New contributor




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                                              answered 14 hours ago









                                              ThanushanThanushan

                                              91




                                              91




                                              New contributor




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                                              New contributor





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                                              • $begingroup$
                                                who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                                                $endgroup$
                                                – user6760
                                                14 hours ago






                                              • 1




                                                $begingroup$
                                                Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
                                                $endgroup$
                                                – L.Dutch♦
                                                14 hours ago










                                              • $begingroup$
                                                This (handwavium waves) is the One True Answer.
                                                $endgroup$
                                                – RonJohn
                                                13 hours ago


















                                              • $begingroup$
                                                who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                                                $endgroup$
                                                – user6760
                                                14 hours ago






                                              • 1




                                                $begingroup$
                                                Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
                                                $endgroup$
                                                – L.Dutch♦
                                                14 hours ago










                                              • $begingroup$
                                                This (handwavium waves) is the One True Answer.
                                                $endgroup$
                                                – RonJohn
                                                13 hours ago
















                                              $begingroup$
                                              who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                                              $endgroup$
                                              – user6760
                                              14 hours ago




                                              $begingroup$
                                              who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                                              $endgroup$
                                              – user6760
                                              14 hours ago




                                              1




                                              1




                                              $begingroup$
                                              Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
                                              $endgroup$
                                              – L.Dutch♦
                                              14 hours ago




                                              $begingroup$
                                              Actually we started using electromagnetic waves from the very moment we learned how to make fire, which is an electromagnetic wave emitter.
                                              $endgroup$
                                              – L.Dutch♦
                                              14 hours ago












                                              $begingroup$
                                              This (handwavium waves) is the One True Answer.
                                              $endgroup$
                                              – RonJohn
                                              13 hours ago




                                              $begingroup$
                                              This (handwavium waves) is the One True Answer.
                                              $endgroup$
                                              – RonJohn
                                              13 hours ago











                                              0












                                              $begingroup$

                                              You could ask them.



                                              Sure, this wont work in every situation. But if they cooperate, it's the best way. Your communications range is probably further than your sensor range, and you'll get the most accurate possible answer. Their computer will have to have the exact mass measurement at all times.






                                              share|improve this answer









                                              $endgroup$


















                                                0












                                                $begingroup$

                                                You could ask them.



                                                Sure, this wont work in every situation. But if they cooperate, it's the best way. Your communications range is probably further than your sensor range, and you'll get the most accurate possible answer. Their computer will have to have the exact mass measurement at all times.






                                                share|improve this answer









                                                $endgroup$
















                                                  0












                                                  0








                                                  0





                                                  $begingroup$

                                                  You could ask them.



                                                  Sure, this wont work in every situation. But if they cooperate, it's the best way. Your communications range is probably further than your sensor range, and you'll get the most accurate possible answer. Their computer will have to have the exact mass measurement at all times.






                                                  share|improve this answer









                                                  $endgroup$



                                                  You could ask them.



                                                  Sure, this wont work in every situation. But if they cooperate, it's the best way. Your communications range is probably further than your sensor range, and you'll get the most accurate possible answer. Their computer will have to have the exact mass measurement at all times.







                                                  share|improve this answer












                                                  share|improve this answer



                                                  share|improve this answer










                                                  answered 8 hours ago









                                                  LukeLuke

                                                  1,778511




                                                  1,778511























                                                      0












                                                      $begingroup$

                                                      Equipment that can survey the gravitational potential on the order of microgals is quite common today in geological industry and academia, known as gravimetry.



                                                      The machines used as instrumentation, gravimeters, are quite interesting, but ultimately they are able to derive densities by way of directly measuring differing gravitational acceleration at many points. These have even been used to probe non-geological manmade-scale objects e.g. when French scientists surveyed the Cheops pyramid for unknown chambers.



                                                      A tech advanced gravimeter (perhaps using an array of atom chip nano gravimeters) paired with a good gravimetric map of the navigation area should allow measurement of the mass of an anomalous body. With enough resolution you could even possibly map the density distribution of the vessel and track masses moving on the interior.






                                                      share|improve this answer










                                                      New contributor




                                                      joshperry is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                                      Check out our Code of Conduct.






                                                      $endgroup$


















                                                        0












                                                        $begingroup$

                                                        Equipment that can survey the gravitational potential on the order of microgals is quite common today in geological industry and academia, known as gravimetry.



                                                        The machines used as instrumentation, gravimeters, are quite interesting, but ultimately they are able to derive densities by way of directly measuring differing gravitational acceleration at many points. These have even been used to probe non-geological manmade-scale objects e.g. when French scientists surveyed the Cheops pyramid for unknown chambers.



                                                        A tech advanced gravimeter (perhaps using an array of atom chip nano gravimeters) paired with a good gravimetric map of the navigation area should allow measurement of the mass of an anomalous body. With enough resolution you could even possibly map the density distribution of the vessel and track masses moving on the interior.






                                                        share|improve this answer










                                                        New contributor




                                                        joshperry is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                                        Check out our Code of Conduct.






                                                        $endgroup$
















                                                          0












                                                          0








                                                          0





                                                          $begingroup$

                                                          Equipment that can survey the gravitational potential on the order of microgals is quite common today in geological industry and academia, known as gravimetry.



                                                          The machines used as instrumentation, gravimeters, are quite interesting, but ultimately they are able to derive densities by way of directly measuring differing gravitational acceleration at many points. These have even been used to probe non-geological manmade-scale objects e.g. when French scientists surveyed the Cheops pyramid for unknown chambers.



                                                          A tech advanced gravimeter (perhaps using an array of atom chip nano gravimeters) paired with a good gravimetric map of the navigation area should allow measurement of the mass of an anomalous body. With enough resolution you could even possibly map the density distribution of the vessel and track masses moving on the interior.






                                                          share|improve this answer










                                                          New contributor




                                                          joshperry is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                                          Check out our Code of Conduct.






                                                          $endgroup$



                                                          Equipment that can survey the gravitational potential on the order of microgals is quite common today in geological industry and academia, known as gravimetry.



                                                          The machines used as instrumentation, gravimeters, are quite interesting, but ultimately they are able to derive densities by way of directly measuring differing gravitational acceleration at many points. These have even been used to probe non-geological manmade-scale objects e.g. when French scientists surveyed the Cheops pyramid for unknown chambers.



                                                          A tech advanced gravimeter (perhaps using an array of atom chip nano gravimeters) paired with a good gravimetric map of the navigation area should allow measurement of the mass of an anomalous body. With enough resolution you could even possibly map the density distribution of the vessel and track masses moving on the interior.







                                                          share|improve this answer










                                                          New contributor




                                                          joshperry is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                                          Check out our Code of Conduct.









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