Apollo Discussions > The Reality of Apollo
LM APS question
Allan F:
Was the APS designed to be fired more than once? I think at least 2 burns with the APS was needed - one to get off the ground and up to altitude and speed for orbital insertion, and one to circularize the orbit. And maybe a few to change the orbtial plane.
Or was the RCS able to handle those burns?
bknight:
I believe it was only fired once, since it had to be rebuilt each time it was fired one Earth, corrosive fluids.
https://en.wikipedia.org/wiki/Ascent_propulsion_system
ETA: However it was successfully fired twice during A9
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730010173.pdf
Page 22
QuietElite:
There was at least another additional burn with the APS for Apollo 14-17 since these missions used the Direct Rendezvous approach instead of the Coelliptic Method like earlier missions.
The deltaV change of the TPI burn is higher for Direct Rendezvous since it missed additional burns that would have already raised the Periapsis of the Orbit. Therefore they used the APS instead of RCS otherwise the burn would take very long.
Allan F:
Thank you for your input.
VQ:
--- Quote from: bknight on March 01, 2019, 04:07:51 PM ---I believe it was only fired once, since it had to be rebuilt each time it was fired one Earth, corrosive fluids.
--- End quote ---
No, it could be fired multiple times. They just didn't want to have it an anything other than pristine condition at the start of a mission. Per the wiki you linked, the APS's immediate predecessor, the Bell 8247 (which used the same fuel) could be restarted at least 15 times.
The LM RCS and APS tanks were crossfed, so after the first (main) burn all dV maneuvers could be performed with either system. So the APS was only life-safety critical for the first burn.
I believe the APS was re-fired a final time on most missions after the crew left it, to deorbit the ascent stage (either back to the lunar surface or to heliocentric orbit).
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