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# Can sattelites be kept in a stable orbit in a planet-moon system? watch

1. There are some points in a three body system were the system will be stable. However, I wondered if it is possible to obtain a stable configuration if you let a sattelite go some orbit were it dies not lie in these points. The relative distances between the boddies must not be constant, the only requirement is that the sattelite would maintain a stable path in a planet - moon system. I was thinking perhaps teh sattelite could orbit the system having the moon and the planet in the two centres of an elipse, or perhaps it could do something close to a figure 8 loop around teh two boddies (Btw, the moon and the planet onviously orbit a common centre of mass.) I assume that the effect of the sattelites gravitation on the planet/moon is neglectable.
2. (Original post by Jonatan)
(Btw, the moon and the planet onviously orbit a common centre of mass.)
Last time I worked it out, the null point (for gravity) was 3.42x10^8 m away from the earth. Which is about 0.4x10^8 m from the moon.
3. (Original post by 2776)
Last time I worked it out, the null point (for gravity) was 3.42x10^8 m away from the earth. Which is about 0.4x10^8 m from the moon.
Yes, there are nullpoints (Four of them actually) where a sattelite can remain in stable orbit around the Moons and the earths common point of orbit, but I wondered if there is some sort of path the sattelite could follow in such a way that it was stable without being constantly at a nullpoint (It could cross the nullpoints in its path, but it should not simply rest there).
4. Hmm, good question. I need to ahve a good think about it...
5. Could the satellite have a 28 day orbit so the earth is alway eclipsing the moon from the satellite? That way the satellite's weight due to the earth and the moon would act in the same direction and simplfy the problem. But probably the satellite would have to have a very large orbit
6. (Original post by mik1a)
Could the satellite have a 28 day orbit so the earth is alway eclipsing the moon from the satellite? That way the satellite's weight due to the earth and the moon would act in the same direction and simplfy the problem. But probably the satellite would have to have a very large orbit
for a 28 day orbit it would need to be quite far away from the earth (right inside the moon, in fact)
7. (Original post by mik1a)
Could the satellite have a 28 day orbit so the earth is alway eclipsing the moon from the satellite? That way the satellite's weight due to the earth and the moon would act in the same direction and simplfy the problem. But probably the satellite would have to have a very large orbit
No, cus then it would have to be at the same distance as the moon. This woudl also imply that the moons gravity and that of teh earth would have to cancel, and so the sattelite would have to be at aone of the stable points...

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