Trying to work out mechanics and visuals from one of two moons orbiting a gas giant. My idea is that the moons are tidally locked so they can never see each other's backsides, but this might be achieved by a different type of orbit. I just want these twin moons to maintain close proximity and they circle a gas giant and need to figure out how Moon A could hide the construction of a space station from its sister moon, Moon B.
Orbital Mechanics Perspective: Yes, This is Possible
I can say with a fair amount of confidence that this is possible from an orbital mechanics perspective. Two moons could orbit each other while orbiting a larger body. From a moon-formation perspective, I'm not sure if this is particularly possible or not.
If you fool around with some orbit simulators- this one or this one, you could find a configuration that works. Don't worry about making a gas giant orbit around a sun, and then placing your two moons.
If you take the first simulator, change the number of bodies to 3, and make the mass of the third body 10, it can approximate the setup you want. (Alternatively: for body two, have a mass of 1 and a distance of 140; body 3 has a mass of 1 and distance of 145.)
Tidal locking in not hard to achieve- it just takes some time.
Moon Formation Perspective: Also Possible
A Note: for most stories, the specifics of orbit are not as important, just that the configuration is possible.
This scenario is possible, but it relies heavily on how far away the moons are from the gas giant. A statelite cannot be tidally locked to two different bodies, whichever one has the greatest tidal forces acting on it will be the tidal lock "winner". Its why Pluto and Charon can be locked while still orbiting the sun. Since the tidal forces of the gas giant will decrease as we increase the distance, with enough space this setup can work.
Its hard to say, but I think this setup could work on a system that's a similar distance Iapetus is from Saturn. Though this relies on a lot of factors such as the mass of the three bodies in question and whether any other moons throw this delicate setup off balance.
Yes, it's possible.
There is no limit to the number of sub-satellites a system can have. A sun can have a planet, a planet can have a moon, a moon can have its own satellite, and then that satellite can have its own sub-satellite, and so on.
It all has to do with the Hill sphere of the orbiting body, which describes the distance in which a satellite can exist in a stable orbit. Outside of the Hill sphere, the more massive body's influence is too great.
What you describe is known as the 3 body problem. Stability in such a system is dreadfully difficult. The best bet you would have is with one of Euler's solutions, which require all 3 bodies to be co linear at every moment. Other than that, there's very few stable cases.
- If one body is of inconsequential mass (such as a spaceship in a system with a planet and the sun), there are stable solutions.
- A few dozen special cases have been discovered with special mass or orbit limitations.