Would it be possible to put a satellite into the same orbit as the Moon, but far enough ahead or behind the Moon to remain in place?
Has this ever been done in practice?
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1$\begingroup$ It looks like it's already been done: en.wikipedia.org/wiki/… Or at least, it's planned to put satellutes in the Earth-Moon L4 & L5 points. $\endgroup$– PM 2RingJul 20, 2019 at 22:23
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6$\begingroup$ This is a really interesting question, but I'm voting to close this question as off-topic because it's about a potential artificial satellite mission itself, and not about Astronomy. See What types of questions should I avoid asking? and also What topics can I ask about here? However it's a great question for Space SE! $\endgroup$– uhohJul 20, 2019 at 22:53
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4$\begingroup$ I will vote to reopen if this question is closed. This question is on-topic, particularly when generalized beyond the Earth-Moon system. $\endgroup$– David HammenJul 21, 2019 at 11:55
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$\begingroup$ The reason I asked this question is because it would be a way of establishing communication on the far side of the moon. I don't want to consider the Lagrange points, I was wondering if a satellite could follow the same orbit as the moon. It would have to be far enough ahead or behind to be unaffected by the moon. Would it still be in sight of the moon (i.e non the less close enough). Could an object follow the moon's orbit? $\endgroup$– BingohankJul 21, 2019 at 18:11
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$\begingroup$ This question might be of relevance then: astronomy.stackexchange.com/q/29012/24157 $\endgroup$– user24157Jul 22, 2019 at 17:40
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3 Answers
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Yes. Trojan orbits (60° before or after the Moon) are even stable in most cases. These points are called the L₄ and L₅ points, which are two of the five Lagrangian points.
These orbits are mostly impractical (nothing is there).
Today the most known is the Chinese Queqiao satellite, which is a communication relay to their probe on the far side of the Moon. Instead of using L₄ or L₅, Queqiao is in a halo orbit around another Lagrangian point; Earth-Moon L₂.
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Has this ever been done in practice?
Not intentionally, and not by humankind. But by nature, the answer is yes. Thousands of objects are known to co-orbit with Jupiter about the Sun-Jupiter L4 and L5 points, millions are thought to exist. Trojans (the generic name for small objects that co-orbit with a somewhat large object about an even larger object, with the small objects in pseudo orbits about the triangular Lagrange points) are known to exist for Neptune, Mars, Uranus, and Earth. Two of Saturn's moons, Tethys and Dione, have trojans in pseudo orbits about their triangular Lagrange points.
answered Jul 21, 2019 at 12:05
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$\begingroup$ @uhoh See en.wikipedia.org/wiki/Kordylewski_cloud $\endgroup$– PM 2RingJul 21, 2019 at 13:53
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$\begingroup$ @PM2Ring Oh, now that you mention it, I remember reading about the confirmation last year. there was a patch of zodiacal light with a difference in polarization which stayed in the right place. Part I (modeling), Part II (observation). I'd added those here last year, then forgot. Thanks! $\endgroup$– uhohJul 21, 2019 at 16:06
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One limitation of using L4 or L5 is, ironically, their natural stability. They are now known to attract dust clouds. Putting and station-keeping a satellite at the ostensibly unstable Lagrange points avoids having to deal with a higher dust density. In additiin, L1 and L2 offers a closer view of the Moon.
