Stable orbit?

[zhar2]

Im trying to find the stable orbit for a hypothetical moon around a hypothetical planet for a system im doing, The system itself was generated in stargen but the generator fails to give the distance of a moon to its parent planet, it did tell me though that the planet moon had a day of 18.3 hours and i figured that either the moon is far enough to have its own independent rotation from its orbit period or its close enough to be tidaly locked and the 18.3 hours would be the same as its orbit period, using the second assumption i managed to find the distance between the two bodies near 42,000 km but i dont know if it can be right as one body has 2.071 Earth masses and a radius of 8071.9 km, while its moon has a mass of 0.418 Earth masses and a radius of 4794.7 km, i worked out that at that distance the moon was beyond the roche limit so it would remain intact, but i dont know if this orbit could be stable or possible.

Any help of pointer will be sincerelly appreciated.

: )

[zhar2]

Well never mind, i knew it was a bit of a long shoot to ask.

[selden]

Some people use Tony Dunn's Orbit (Gravity) simulator
http://www.orbitsimulator.com/
Some orbital calculators are at
http://orbitsimulator.com/formulas/

[orinetz]

You can use this online 3D browser based simulator
http://orinetz.com/planet/index.php

Orinetz

[bdm]

The system is stable if the planet and moon are both tidelocked to each other, in the style of Pluto and Charon. This is likely because the moon is massive.