Can somebody explain this orbit to me?

[BradHann]

Moon 4A here, appears that, at a certain point in its orbit, is pretty much halfway between the two planets in this binary. Comparing orrery views hours and days apart shows that the moon is definitely moving relative to its parent, so at some point it will end up directly in between the two. And they're pretty close - like mere ls apart. Should this proximity have some sort of effect on the moon's orbit? Would it get close enough to disrupt the rings of planet 5? In the real universe, could such a configuration exist?

I didn't think to take any screenshots while I was there, but if anyone happens to be nearby (it's on the direct path to Colonia) it's not a bad view.

 

[Orvidius]

This is where we see some of the limitations of what StellarForge and the game engine can do. Elite (and pretty much any other space game like this) uses perfect Kepler orbits that are "on rails". That is, the orbital motion makes perfect elliptical shapes and are 100% predictable, and can be calculated in advance to always know where a body will be.

If you notice, planet 5 has a larger orbit around the common barycenter than planet 4 does, which means it's less massive and has a smaller "sphere of influence" than body 4 does. The "sphere of influence" is the area in which a body's gravity is stronger than the pull from anything else in the system. StellarForge can allow other objects to orbit close to that sphere, but not intersecting it (and if it does allow that, ever, it should be considered a bug... and we know of some intersecting bodies, so it can occasionally allow it).

However in reality, this would definitely count as a 3-body problem, and likely would not be a stable configuration. Or it would be stable for a little while, and eventually become unstable. StellarForge acts like a "snapshot in time" in the evolution of a star system, and then locks the orbits into whatever the final configuration was. Most of the time we get reasonable orbits, but occasionally we will see systems that could pass through a specific orbital configuration briefly that is unlikely to be stable, but due to the game's "frozen" orbital evolution and perfect Kepler orbits, we will only ever see it in that one configuration.

 

[Sapyx]

In the real universe, could such a configuration exist?

No. A moon that crosses beyond the barycentric point of a two-planet system is not going to be in a long-term or even short-term stable orbit around one planet or the other. I suspect in a "real-universe" scenario, the moon 4a would most likely end up being ejected into interplanetary space, becoming a planet. There's a chance it might end up locked in the Trojan point at 60 degrees between 4 and 5, or flung out in an orbit that circles both 4 and 5. Trojan moons are possible in ED, but not Trojan-binary planets, and moons orbiting two binary planets also cannot happen.

Space stations in ED are often in such orbits, but one could argue that a station can use their station-keeping thrusters to regularly adjust their orbit and keep their position in their un-natural orbital configuration. Not quite sure why they'd need or want to do this when putting the station into a more stable orbit would be easier and cheaper. But a moon ain't got no engines.

 

[Mrat13]

But a moon ain't got no engines.

That's no moon.....