Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>You would have to have the satellite of the moon in very close orbit in order that the gravitational field of the planet be negligible. That is, in principle, possible as for example the observation that the Earth's moon orbits the Earth, and it only marginally affected by the Sun. But given that moons tend to be fairly close to their respective planets, it would be difficult to have a satellite that clearly orbits the moon, with little effect from the planet.Once you have two gravitational fields affecting a satellite the problem becomes rather complex. You, in fact, are faced with the three body problem and orbital solutions in that case are not known in closed form and require computer simulations. They tend to not be stable orbits. Instability rather precludes long-lived moons of moons.Sure there is enough gravity for an object to orbit the ISS. VERY SLOWLY and VERY CLOSE. Not a practical orbit at all. <br />Posted by DrRocket</DIV><br /><br />After all, there are satellites orbiting our Moon (three in fact at the moment IIRC) but they required very precise velocity and direction to but them there, and the orbits are not stable for very long (history of the solar system wise that is). <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>