LM attitude control at PDI

[PUshift]

Could somebody be so kind to verify weather the LM DPS on its descent on PDI had used its engine gimbal-functionality to change the attitude (i.e. pitch down from 90 to 70°, later to 30° and further down to zero until the horizontal stop) or were all changes of attitude made by firing the RCS quads?
I hope to know for sure that the ascent went on RCS control only.
But so far I believed in the use of gimbal control while descending.

I experienced this as a very precise way to control the vehicle on my trials to land the LM in ORBITER (Apollo NASSP 6.4.3) which surely doesn´t count in any respect.
But like in reality there is a switch called "ENG GIMB" which can be set either to "enabled" or "on". The gimbal control works on "enabled" only (in the simulation).
I suggest that the "on"-position at least allowed the calibration of "centre-of-gravity", for which the DPS engine was initially run at only 10 per cent thrust for the first 26 seconds. (not really simulated in Orbiter).

Now some well experienced people of a german forum tell me that the PDI ran on RCS control only. Gimbaling only for holding centre-of-gravity.
In W.David Woods "How Apollo flew to the moon", page 244 it is mentioned, that the ability to vector the thrust was not intended to steer the craft because it had been to slow for that. So this correlates with the given assertion.

Ok, PC-Simulations don´t give any garantee to copy reality. But the switch existed really, it can be found directly above the famous "descent command override" on the left side of the LM panel. And it had to be worth for something. Was the "enabled"-position any backup for redundancy in case of RCS failure but was never used?

I remind to have read anywhere (cannot remember, where) apollo astronauts described the behavior of the LM control as very effective, directive, "squared" or how it´s been said. Just fitting to the quick changes of attitude by gimbaling which doesn´t only start but also stop the rotation in a very fast and direct manner.

I would like to know the position the "ENG GIMB" switch and how it was done in reality of the apollo missions.

(for the 3 stages of the SaturnV, with that huge weight and inside the atmosphere I cannot imagine any other control of attitude than gimbaling the main engines. If that should be wrong I will loose my whole confidence in the belief to know anything about how apollo worked.)

Thanks a lot in advance!

[Czero 101]

A fairly quick look through the Apollo 11 air-to-ground transcripts finds this:

04:06:28:34 - CMP (COLUMBIA): Eagle, this is Columbia. You're GO for PDI and they recommend you yaw right 10 degrees and try the high gain again.
04:06:28:46 - CMP (COLUMBIA): Eagle, you read Columbia?
04:06:28:48 - LMP (EAGLE): Roger. We read you.
04:06:28:49 - CMP (COLUMBIA): Okay.
04:06:28:51 - CC: Eagle, Houston. We read you now. You're GO for PDI. Over.
04:06:28:57 - LMP (EAGLE): Roger. Understand. AELD control circuit breakers. DECA GIMBAL AC - closed?
04:06:29:07 - CDR (EAGLE): What?
04:06:29:08 - LMP (EAGLE): DECA GIMBAL AC - closed? Circuit breaker? COMMAND OVERRIDE - off? GIMBAL ENABLE? RATE SCALE - 25.
04:06:29:23 - CC: Eagle, Houston. Your alignment is GO on the AGS. On my Mark, 3:30 until ignition.
04:06:29:29 - LMP: (EAGLE) Roger.
04:06:29:33 - CC: Mark.
04:06:29:34 - CC: 3:30 until ignition.

DECA - Descent Engine Control Assembly



Cz

[ka9q]

This is just from memory, but I seem to recall reading that the computer could use both the RCS thrusters and the descent engine gimbal for pitch and roll control. I'd recommend digging through the various papers by the people who programmed the PNGS.

(Yaw, of course, had to be done with the RCS since the yaw axis runs through the engine).

All attitude control during S-IC and S-II flight was by gimbaling the four outboard motors on those stages. Roll control of the S-IVB stage was done by the Auxiliary Propulsion System (APS) thrusters on the sides of the stage; pitch and yaw could be done by gimbaling the single J-2 engine.

This was similar to burns using the SPS on the Service Module; the single engine was gimbaled for pitch and yaw, with the RCS controlling roll.

The SPS gimbals consumed a lot of power, more than the fuel cells could provide, so the entry batteries in the CM were thrown onto the bus to help. They had to be recharged later. Those gimbals were also activated during the later part of the launch in the event that the S-IVB shut down early, but late enough that the SPS could make orbit and carry out an alternate mission.

[Kiwi]

Oct 9, 2010 18:21:00 GMT -4 PUshift said:

Could somebody be so kind to verify weather the LM DPS on its descent on PDI had used its engine gimbal-functionality to change the attitude (i.e. pitch down...) or were all changes of attitude made by firing the RCS quads?

PUshift, have you read the first page of the Apollo 11 Lunar Surface Journal, "The First Lunar Landing"? (Link at the bottom of every page here.)

While it's not spelt out exactly how attitude was attained and by which method, searching that page for "pitch", "gimbal" and "slosh" will at least tell you more about it. Fuel slosh was a factor with Apollo 11 and was fixed with baffles in the fuel tanks for the later landings.

One publication at the ALSJ says on page 4:
"The gimbal drive is controlled automatically by the DAP for slow attitude rate commands. For high rate changes, the DAP controls the RCS..."
NASA TM X-58040 (8.6Mb PDF) NASA Technical Memorandum, "Apollo Lunar Descent and Ascent Trajectories" by Floyd V. Bennett, presented at the AIAA 8th Aerospace Sciences Meeting, NYC, 19-21 January 1970. Planning and post-flight analysis for Apollo 11. Scan by Gary Neff.


Anyone who is interested in Apollo, including hoax-believers, should study at least that first Apollo 11 page at the ALSJ. Doing so might relieve some of the HBs of their ignorance.

I found it fascinating to read about all that stuff I listened to live on the radio back on the morning of 21 July 1969 (NZST). I didn't understand all the jargon, but with the help of the Public Affairs Officer at least got the overall picture and understood the drama of such a momentous event in the history of our planet.

[PUshift]

Oct 13, 2010 8:28:34 GMT -4 Kiwi said:

Oct 9, 2010 18:21:00 GMT -4 PUshift said:

...

PUshift, have you read the first page of the Apollo 11 Lunar Surface Journal, "The First Lunar Landing"? (Link at the bottom of every page here.)
...

Sounds right as a logical hint. ALSJ was known but it´s true I didn´t attempt to find it there by myself. Others seemed to have looked up there already, we came into a discussion (other forum) and I mentioned my experiences in running a simulation. I appreciate to learn how far it is coming close to reality. Beeing a lawman but very interested.
Suitably my german forum-partners have stated this question to Mr. Paul Fjeld (history.nasa.gov/alsj/fjeld.html) , putting it on any "internal ALSJ-Mailing list", as they said.
If an answer should be obtainable I would post it here.
Thanks