We all know that the LEM descended from the CSM to the moon's surface and then rose back again to dock with it. But there are some videos that show the CSM floating in the foreground with the moon's surface in the background. This was obviously shot from the LEM, which must have been at a higher altitude than the CSM. Hence my question - Did the LEM ever rise above the orbit of the CSM at any time?
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$\begingroup$ It would be great if you showed us that video or image. $\endgroup$– Star ManCommented Aug 7, 2019 at 18:46
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$\begingroup$ At close range, a few meters in altitude difference would be enough to show up in photos. But I suspect altitude data wasn't kept to that precision. $\endgroup$– HobbesCommented Aug 7, 2019 at 18:59
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$\begingroup$ Do an elliptical orbit with apoapsis few centimeters above the CSM count? $\endgroup$– Manu HCommented Aug 7, 2019 at 19:04
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2$\begingroup$ The fact that this picture exists answers your question. $\endgroup$– Star ManCommented Aug 7, 2019 at 19:59
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$\begingroup$ If it was decoupled while facing away from the moon, it could feasibly have been above the CSM for a time. $\endgroup$– Magic Octopus UrnCommented Aug 7, 2019 at 20:18
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1 Answer
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Yes.
By separating with the LM moving away from the moon, and the CSM towards it, the LM would be at a higher altitude than the CSM. As a consequence orbital mechanics cause the LM to start to fall behind the CSM, so when the descent engine was fired to slow the LM it wouldn't bump into the CSM.
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5$\begingroup$ This sounds reasonable, but do you have a reference for it? $\endgroup$ Commented Aug 7, 2019 at 20:57
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$\begingroup$ I'm fairly sure it is documented, however the memory comes from a time of my life I have no desire to revisit. $\endgroup$– user20636Commented Aug 8, 2019 at 6:26