ApolloHoax.net
Apollo Discussions => The Reality of Apollo => Topic started by: Mag40 on January 19, 2013, 12:51:42 PM
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A question occurred to me about the orbital path of the CSM over a 3 day period. Since the Moon rotates once over a 28 day period due to tidal locking.....how did they maintain the orbital path to continually overfly the landing zone? Were there corrective burns of the RCS thrusters during each orbit?
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My knowledge of orbital mechanics is slight but I'm pretty sure that, unless the landing zone was smack on the equator, it is not possible to set up an orbit that will pass over the same point on the surface every time... as I recall the SPS was specified and fuelled to allow the SM to do any required orbit changes in the event of an emergency ascent of the ascent stage... which would get itself into an orbit such that the CSM would have the minimum of work to do.
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A question occurred to me about the orbital path of the CSM over a 3 day period. Since the Moon rotates once over a 28 day period due to tidal locking.....how did they maintain the orbital path to continually overfly the landing zone? Were there corrective burns of the RCS thrusters during each orbit?
Yes, they did burns. I'm not sure how many, but it certainly wasn't one per orbit. I think they may have done them as rarely as once only, a couple of orbits prior to LM lift-off, or possibly once a day. The burn(s) would have been done with the SPS engine.
In any case, it wasn't necessary for the CSM to overfly the landing site. If the LM needed to lift off in a hurry, there was plenty of fuel and time for the two spacecraft to make the necessary burns to rendezvous. I'm not sure which spacecraft would do the maneuvering, although I assume for safety reasons either spacecraft would have been able to do it.
Another benefit of not constantly overflying the landing site was that it allowed the CMP to explore more of the Moon's surface. This was particularly useful in the later missions with the cameras mounted in the SIM bay of the Service Module.
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Thanks for the replies! I actually have been delving into this....to try and get more info.... and came across this cool chart showing the ground track for Apollo 12 -
http://www.hq.nasa.gov/alsj/a12/A12_smobtl.JPG