Apollo LM ascent procedure, computer controlled or manual?

Question

How was the Apollo LM ascent launch procedure controlled? Was it manual, semi-automatic or fully automatic? By "launch procedure" I am talking about the pitch control for the LM. I believe there is no thrust control for the LM ascent stage engine, hence correct orbit would only be achieved by pitch control? But again, how was this pitch control performed?

Also, how much room for error was there? During the six successful missions, what was the largest error for lunar rendezvous that occurred?

I'm assuming that the CSM could use its SPS engine to perform any major translations that might be required, but was this ever needed? Beyond that, I'm assuming both the LM and CSM would use RCS fuel for finer granularity translation maneuvers?

Answer 1

Largely automated. Flying the rendezvous by hand on the LM's own resources would have been incredibly hard, although flying it semi-manually with assistance from ground tracking and computers would, in theory, have been possible and the astronauts were provided PADs (lists of times, orientations, etc. for pre-calculated maneuvers) for this eventuality.

The LM ran a series of programs, using data from its own inertial guidance, and a rendezvous radar which measured the distance, radial velocity, and direction to the CM. The programs first got the LM off the ground and into a safe lunar orbit, then performed a series of phasing and plane-change maneuvers to match orbits with the CM over the course of about two orbits. The initial ascent to orbit was performed using the APS engine, and allowed a fairly wide margin for error; all of the later rendezvous maneuvers were performed using RCS, and involved delta Vs on the order of a few meters per second.

The CM had its own matching set of programs that computed the maneuvers from the CM's point of view, using its own instruments. While for the most part, the output of these programs was mostly used as a double-check on the LM's navigation, it was possible for the CM to "swoop in" and rendezvous with an LM that was unable to maneuver, once the LM had reached orbit. This never actually occurred.

All of the programs I've mentioned ran on the primary computer (aka LM Guidance Computer or Primary Navigation and Guidance System), but the LM also carried a second computer, simpler but in theory more reliable, called the Abort Guidance System, that was capable of carrying out these maneuvers.

The computer programs would bring the LM to within about a mile of the CM at a small closing velocity, at which point semi-manual control begins, with the computer maintaining an orientation pointing towards the CM, and the astronaut using data from the radar as well as eyeballs to bring the LM to rest a few feet away from the CM. The CM then maneuvers by hand and eye to dock with the LM.

This essay on Lunar Orbit Rendezvous on the NASA Apollo Flight Journal provides a lot of useful information.

Answer 2

This written by Robert F. Stengel for the Journal of Spacecraft and Rockets is a very well documented abstract that provides a great amount of detail about all of the attitude control of the Lunar Module.

There is so much detail, that instead of quoting it I will let you read it. I think you will find a lot of answers in there!

If that's not enough, there is even more great info Here on spaceref.com in an article titled "Apollo Lunar Module Landing Strategy".

I hope that this helps! Let me know if it doesn't and I can try to help hunt down answers to this since it's an interesting question.

Answer 3

In response to the comment above you can also check out one more article found on SpaceRef.com

The article is titled " Apollo Lunar Module Landing Strategy" and can be found Here

At staging, the control power of the ascent stage is about 35 deg/sec2 for pitch and roll attitude maneuvers. Under emergency manual control where the pilot deflects his attitude hand controller hard-over, there is no attitude rate limitation. Normal manual control commands are limited to 20° /sec and automatic control limited to 10° /sec in pitch and 5° /sec in roll. These attitude rate limitations are important from the standpoint of determining how quickly the ascent stage attitude can be returned to the vertical in the event of an impending tipover.

This is one small detail, but this article does talk about ascent in much greater detail and the control that the astronaut would have. I do not think that it mentions the margin of error. It is a very long article, so it might be in there somewhere that I over looked. So yes, they are able to control pitch and yaw, etc but this is the most detail that I can find at the moment so I hope that it explains the "how" a little bit.

A lot of the information about this refers to aborts, but the mechanics are mainly the same.