LM descent orbit insertion?

[Willoughby]

Hey guys.  I was going through the mission timelines the other day and I came across something I am confused about.  Particularly on the Apollo 11 and 12 missions.  After the undocking of the CSM/LM in lunar orbit, it seems there was a burn to separate the CSM and LM.  This burn occurred at GET 100:39:52 and 108:24:36 respectively (links to timelines below).  What confuses me is that about an hour after this maneuver (101:36:14 and 109:23:39 respectively) it appears there was another burn to put the craft [back] into orbit.  And it's a significant burn - about 30 seconds.  I assume this is because the separation maneuver was significant enough to de-orbit, and they needed the burn to get back into orbit.  What confuses me is that they call it "descent orbit insertion maneuver" and then note that the "SPS" engine is executing the burn.  However, they've already separated at this point, so I don't understand what's going on here.  Can someone please explain what this is - and the reason for doing this - and why this was a procedure apparently only used for Apollo 11 and 12?  I'd really appreciate it.

Thanks!

https://www.history.nasa.gov/SP-4029/Apollo_11i_Timeline.htm

https://history.nasa.gov/SP-4029/Apollo_12i_Timeline.htm


 

[ajv]

The LM decent procedures started from an approximately 60 nautical mile circular orbit.

For Apollo 10, 11 and 12 the CSM and LM separated and the LM then performed a descent orbit burn to get into a 60x9 orbit with the 9 being the point from where the LM would perform the final powered descent burn. The descent orbit burn was performed by the DPS.

From Apollo 14 onwards the docked CSM/LM spacecraft performed the 60x9 maneuver using the CSM SPS and then they undocked and the CSM would fire the SPS to get back up to the 60x60.

[Willoughby]

Thank you.  This makes total sense.  Then then either timline has a typo or im missing something because it says the SPS engine performs the burn on Apollo 11 and 12 when it would necessarily have been the DPS engine if what you say is accurate (and I believe it is).

[QuietElite]

Yeah it is a typo, it should be the DPS for the descent orbit insertion on Apollo 11 and 12. The seperation maneuver was done by the RCS.