How spaceships determine each other's mass in space?How far can we go? (Space travels)How fast could...

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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







share|improve this question











$endgroup$








  • 4




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    11 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
    11 hours ago






  • 13




    $begingroup$
    @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
    11 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
    8 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
    8 hours ago


















20












$begingroup$


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











$endgroup$








  • 4




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    11 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
    11 hours ago






  • 13




    $begingroup$
    @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
    11 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
    8 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
    8 hours ago
















20












20








20


3



$begingroup$


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 4 hours ago









Glorfindel

3951514




3951514










asked 13 hours ago









user6760user6760

12.9k1571157




12.9k1571157








  • 4




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    11 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
    11 hours ago






  • 13




    $begingroup$
    @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
    11 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
    8 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
    8 hours ago
















  • 4




    $begingroup$
    Do you mind me asking . . . why would you need to know?
    $endgroup$
    – Binary Worrier
    11 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
    11 hours ago






  • 13




    $begingroup$
    @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
    11 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
    8 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
    8 hours ago










4




4




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




$begingroup$
Do you mind me asking . . . why would you need to know?
$endgroup$
– Binary Worrier
11 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
11 hours ago




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




13




13




$begingroup$
@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
11 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
11 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
8 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
8 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
8 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
8 hours ago












10 Answers
10






active

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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.






share|improve this answer











$endgroup$









  • 15




    $begingroup$
    "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
    12 hours ago






  • 10




    $begingroup$
    "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
    12 hours ago






  • 2




    $begingroup$
    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
    9 hours ago






  • 1




    $begingroup$
    @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
    9 hours ago










  • $begingroup$
    If the ship is very small, you could shoot it with a laser and measure the response.
    $endgroup$
    – p.s.w.g
    4 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.






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
    12 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
    12 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
    12 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
    12 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
    11 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.






share|improve this answer









$endgroup$













  • $begingroup$
    What If the're also doing the same thing? It could affect the measurement...
    $endgroup$
    – user000001
    4 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
    2 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).






share|improve this answer









$endgroup$





















    3












    $begingroup$

    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









    $endgroup$









    • 2




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



















    3












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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.






    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
      4 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.






    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
      2 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!






    share|improve this answer









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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




      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
        7 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♦
        7 hours ago










      • $begingroup$
        This (handwavium waves) is the One True Answer.
        $endgroup$
        – RonJohn
        5 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









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        10 Answers
        10






        active

        oldest

        votes








        10 Answers
        10






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        29












        $begingroup$

        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











        $endgroup$









        • 15




          $begingroup$
          "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
          12 hours ago






        • 10




          $begingroup$
          "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
          12 hours ago






        • 2




          $begingroup$
          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
          9 hours ago






        • 1




          $begingroup$
          @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
          9 hours ago










        • $begingroup$
          If the ship is very small, you could shoot it with a laser and measure the response.
          $endgroup$
          – p.s.w.g
          4 hours ago
















        29












        $begingroup$

        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











        $endgroup$









        • 15




          $begingroup$
          "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
          12 hours ago






        • 10




          $begingroup$
          "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
          12 hours ago






        • 2




          $begingroup$
          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
          9 hours ago






        • 1




          $begingroup$
          @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
          9 hours ago










        • $begingroup$
          If the ship is very small, you could shoot it with a laser and measure the response.
          $endgroup$
          – p.s.w.g
          4 hours ago














        29












        29








        29





        $begingroup$

        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 8 hours ago

























        answered 12 hours ago









        PhilippPhilipp

        30.9k1264118




        30.9k1264118








        • 15




          $begingroup$
          "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
          12 hours ago






        • 10




          $begingroup$
          "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
          12 hours ago






        • 2




          $begingroup$
          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
          9 hours ago






        • 1




          $begingroup$
          @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
          9 hours ago










        • $begingroup$
          If the ship is very small, you could shoot it with a laser and measure the response.
          $endgroup$
          – p.s.w.g
          4 hours ago














        • 15




          $begingroup$
          "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
          12 hours ago






        • 10




          $begingroup$
          "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
          12 hours ago






        • 2




          $begingroup$
          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
          9 hours ago






        • 1




          $begingroup$
          @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
          9 hours ago










        • $begingroup$
          If the ship is very small, you could shoot it with a laser and measure the response.
          $endgroup$
          – p.s.w.g
          4 hours ago








        15




        15




        $begingroup$
        "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
        12 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
        12 hours ago




        10




        10




        $begingroup$
        "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
        12 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
        12 hours ago




        2




        2




        $begingroup$
        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
        9 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
        9 hours ago




        1




        1




        $begingroup$
        @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
        9 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
        9 hours ago












        $begingroup$
        If the ship is very small, you could shoot it with a laser and measure the response.
        $endgroup$
        – p.s.w.g
        4 hours ago




        $begingroup$
        If the ship is very small, you could shoot it with a laser and measure the response.
        $endgroup$
        – p.s.w.g
        4 hours ago











        18












        $begingroup$

        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
          12 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
          12 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
          12 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
          12 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
          11 hours ago
















        18












        $begingroup$

        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
          12 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
          12 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
          12 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
          12 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
          11 hours ago














        18












        18








        18





        $begingroup$

        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 13 hours ago









        DarthDonutDarthDonut

        2,007214




        2,007214








        • 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
          12 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
          12 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
          12 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
          12 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
          11 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
          12 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
          12 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
          12 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
          12 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
          11 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
        12 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
        12 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
        12 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
        12 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
        12 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
        12 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
        12 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
        12 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
        11 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
        11 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









        $endgroup$













        • $begingroup$
          What If the're also doing the same thing? It could affect the measurement...
          $endgroup$
          – user000001
          4 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
          2 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









        $endgroup$













        • $begingroup$
          What If the're also doing the same thing? It could affect the measurement...
          $endgroup$
          – user000001
          4 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
          2 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 12 hours ago









        L.Dutch♦L.Dutch

        86.3k29201421




        86.3k29201421












        • $begingroup$
          What If the're also doing the same thing? It could affect the measurement...
          $endgroup$
          – user000001
          4 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
          2 hours ago




















        • $begingroup$
          What If the're also doing the same thing? It could affect the measurement...
          $endgroup$
          – user000001
          4 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
          2 hours ago


















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






        $begingroup$
        What If the're also doing the same thing? It could affect the measurement...
        $endgroup$
        – user000001
        4 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
        2 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
        2 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 9 hours ago









            LSerniLSerni

            28.1k24989




            28.1k24989























                3












                $begingroup$

                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









                $endgroup$









                • 2




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
















                3












                $begingroup$

                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









                $endgroup$









                • 2




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














                3












                3








                3





                $begingroup$

                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 8 hours ago









                RenanRenan

                49.5k13115248




                49.5k13115248








                • 2




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














                • 2




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








                2




                2




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




                $begingroup$
                Sounds good until you find out they have a more powerful laser.
                $endgroup$
                – prl
                4 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
                  4 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
                  4 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 7 hours ago

























                answered 8 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
                  4 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
                  4 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
                4 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
                4 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
                  2 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
                  2 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




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






                $endgroup$



                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








                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.









                share|improve this answer



                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.









                answered 7 hours ago









                JDrummJDrumm

                411




                411




                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.





                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.






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












                • $begingroup$
                  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
                  2 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
                  2 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
                2 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
                2 hours ago











                1












                $begingroup$

                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









                $endgroup$


















                  1












                  $begingroup$

                  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









                  $endgroup$
















                    1












                    1








                    1





                    $begingroup$

                    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 13 mins ago









                    codeMonkeycodeMonkey

                    2,894816




                    2,894816























                        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
                          7 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♦
                          7 hours ago










                        • $begingroup$
                          This (handwavium waves) is the One True Answer.
                          $endgroup$
                          – RonJohn
                          5 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
                          7 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♦
                          7 hours ago










                        • $begingroup$
                          This (handwavium waves) is the One True Answer.
                          $endgroup$
                          – RonJohn
                          5 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.
                        Check out our Code of Conduct.









                        share|improve this answer



                        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.









                        answered 7 hours ago









                        ThanushanThanushan

                        91




                        91




                        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.





                        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.






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












                        • $begingroup$
                          who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                          $endgroup$
                          – user6760
                          7 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♦
                          7 hours ago










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


















                        • $begingroup$
                          who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                          $endgroup$
                          – user6760
                          7 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♦
                          7 hours ago










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
















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




                        $begingroup$
                        who knows maybe someone somewhere somehow invents twin blackhole drives... we'll need your help then.
                        $endgroup$
                        – user6760
                        7 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♦
                        7 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♦
                        7 hours ago












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




                        $begingroup$
                        This (handwavium waves) is the One True Answer.
                        $endgroup$
                        – RonJohn
                        5 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 1 hour ago









                            LukeLuke

                            1,778511




                            1,778511






























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