Author Topic: Using the RCS for translational movement in the LM  (Read 2001 times)

Offline Peter B

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Using the RCS for translational movement in the LM
« on: December 22, 2023, 01:28:13 AM »
Hi everyone

Just seen a question on YT which I thought I'd refer to the Brains Trust.

The poster suggested that the RCS on the complete LM (Ascent Stage plus Descent Stage) couldn't be used for translational movement except in the vertical axis, because the RCS engines were all on the Ascent Stage. That is, the RCS on the complete LM could only be used for rotational movement.

That sounds right, but it also sounds like it wouldn't be a problem, as the intact LM wouldn't have had to make any translational movements except moving away from the CSM.

Is that the case? Or have I missed something?

Thank you!
Ecosia - the greenest way to search. You find what you need, Ecosia plants trees where they're needed.

Offline Allan F

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Re: Using the RCS for translational movement in the LM
« Reply #1 on: December 22, 2023, 08:03:06 AM »
Yes, the full-up LM would be unsteerable, if the rotational forces wasn't countered by the RCS. Imagine you translate left, and start a counter-clockwise spin. All you need is a small clockwise impulse to counter that. That's what the gyroscope was for. To ensure the LM was pointing the correct way.
« Last Edit: December 22, 2023, 08:04:57 AM by Allan F »
Well, it is like this: The truth doesn't need insults. Insults are the refuge of a darkened mind, a mind that refuses to open and see. Foul language can't outcompete knowledge. And knowledge is the result of education. Education is the result of the wish to know more, not less.

Offline Jason Thompson

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Re: Using the RCS for translational movement in the LM
« Reply #2 on: December 25, 2023, 02:29:44 PM »
By no means an expert but it seem to me you can use the other RCS quads to cancel the rotation. Their suggestion seems to assume you can only fire one set in one direction at any given time, which I'm pretty sure is not the case.

So let's say you want to translate the stacked LM forward. You fire the rear-facing RCS thrusters. That sets up a rotational motion around the centre of gravity because the RCS is above it. So you then fire the downward-pointing RCS thrusters on the front side of the LM to counter that. Problem solved.
"There's this idea that everyone's opinion is equally valid. My arse! Bloke who was a professor of dentistry for forty years does NOT have a debate with some eejit who removes his teeth with string and a door!"  - Dara O'Briain

Offline bknight

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Re: Using the RCS for translational movement in the LM
« Reply #3 on: December 25, 2023, 06:03:22 PM »
Some/all of these translational problems were solved after A12 with some new codes so that the LM automatically "corrected"
I had a "discussion" with Derek Willis? concerning Apollo Moon landings both here and on the Unexplained Mysteries forum.  He claimed that he met a man named "John' who "knew" that the Apollo computer hardware and software were not capable of landing until after A12  These notes show some of the work that went into programs during Apollo.

ETA:  Here is the thread
I recently published an article on the website describing what I consider to be "anomalies" with the account of how the Apollo 12 astronauts Pete Conrad and Al Bean examined the Surveyor 3 lander.

I was asked by some members of the Unexplained Mysteries forum if I would join ApolloHoax and debate the issue here. I am happy to that, and will attempt to answer any questions. The article can be found here:

It would be helpful if people looked at the article before commenting, as that would save me from having to explain what it is all about.
« Last Edit: December 25, 2023, 06:15:23 PM by bknight »
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan