Apollo 11: Torque & Thrust of LM RCS Systems

In summary: The main engine on the lander was gimballed, meaning it could swivel to control the direction of thrust. This allowed for more precise control over the craft's movement and helped with stability during landing. However, due to the relatively short duration of the lander's flight, it was not used for thrust vectoring as much as on the Saturn V rocket during launch.
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darkdave3000
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TL;DR Summary
Is angular acceleration by torque reduced if the object in question is also accelerating linearly by rocket thrust? For example, if the "Eagle" from Apollo 11 was firing it's main rockets, will it impede rotation by RCS?
I'm writing a simulation software for the Apollo 11 missions, I'm not allowed to mention my website because of forum rules but you can see it in my profile.

I am trying to now implement the RCS systems into the LM. The LM is the lander such as the one called "The Eagle" in Apollo 11. What I want to know is if firing the main rockets will weaken the torque caused my RCS rotating the LM. Or if RCS torque will be completely unaffected and the spacecraft will rotate at the same angular acceleration and resulting angular velocity even with the main rockets at full thrust.

Also can anyone tell me the distance from center of gravity of the LM the RCS thrusters are so I can calculate the torque? I have the numbers for Newtons for thrust from each RCS rocket but I don't have the distance from COG of it to calculate the resulting torque from said thrust. I assume rotations are caused by 4 RCS thrusters at any time? So I have to multiply the force x 4? For example, if the LM rotats left then the two on the left both toward the viewer and away with fire the top thrusters and the 2 on the right will fire two similarly mentioned RCS thrusters but fire the ones poinging down?
 
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darkdave3000 said:
Summary:: Is angular acceleration by torque reduced if the object in question is also accelerating linearly by rocket thrust? For example, if the "Eagle" from Apollo 11 was firing it's main rockets, will it impede rotation by RCS?
Ideally, "no". Practically, perhaps "yes".

As long as the main engine thrust is aligned with the center of mass of the object, it will have zero torque about that center of mass. Accordingly, main engine thrust will not affect the angular momentum of the craft about the craft's center of mass and, consequently, will not affect its pitch or yaw rate.

That said, I have no practical experience with how well main engine thrust is actually aligned with craft center of mass. But I do know that thrust vectoring is a thing.
 
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Back in those days there was no thrust vectoring correct? May I assume thrust vectoring means the main rocket can cause the ship to change directions by swiveling the nozzle?
 
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darkdave3000 said:
Back in those days there was no thrust vectoring correct? May I assume thrust vectoring means the main rocket can cause the ship to change directions by swiveling the nozzle?
What I picked up from Wikipedia when I tried to sharpen my understanding to properly answer your question was that vanes in the exhaust stream were one of the first ways to achieve a useful effect. I'd always assumed the main purpose is to keep the craft stable during launch.

Back in the day (ancient chinese rockets) you would likely have to fall back on fin stabilization or spin stabilization.
 
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I thought the main engine of the lander was gimballed. I recall reading that Alan Bean (I think) described it as "a sporty ride".
 
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Ibix said:
The main engine of the lander was gimballed, as I recall. I think Alan Bean described it as "a sporty ride".
With a better search term to Google with, it is easy to confirm that recollection.
https://en.wikipedia.org/wiki/Descent_propulsion_system said:
used hypergolic propellants and a gimballed pressure-fed ablative cooled engine that was capable of being throttled.
 
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Does anyone happen to know the distance from COG to RCS on the Apollo 11 Lunar Lander?
 
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darkdave3000 said:
Back in those days there was no thrust vectoring correct? May I assume thrust vectoring means the main rocket can cause the ship to change directions by swiveling the nozzle?
That is what thrust vectoring is, and it was indeed a thing on the Apollo rockets.
 

1. What is the purpose of the LM RCS systems on Apollo 11?

The LM RCS (Reaction Control System) was designed to provide attitude control and maneuvering capabilities for the Lunar Module (LM) during its descent and ascent to and from the lunar surface. It consisted of 16 small rocket engines that could be fired individually or in groups to produce thrust in different directions.

2. How much torque and thrust did the LM RCS systems produce?

The LM RCS engines had a combined total thrust of 3,500 pounds and could produce a maximum torque of 1,000 pound-feet. This was enough to control the LM's orientation and perform precise maneuvers in the low gravity environment of the moon.

3. How were the LM RCS systems controlled?

The LM RCS was controlled by the astronauts using a hand controller and a set of toggle switches located on the control panel. The hand controller allowed the astronauts to adjust the thrust and direction of the engines, while the toggle switches could be used to activate individual engines or groups of engines.

4. Were there any challenges with the LM RCS systems during the Apollo 11 mission?

Yes, there were a few challenges with the LM RCS systems during the Apollo 11 mission. The astronauts had to deal with a malfunctioning engine during their descent to the lunar surface, which caused some unexpected movements and made it difficult to land in the intended location. However, they were able to successfully land the LM despite this issue.

5. How did the LM RCS systems contribute to the success of the Apollo 11 mission?

The LM RCS systems played a crucial role in the success of the Apollo 11 mission. They allowed the astronauts to control the LM's orientation and perform precise maneuvers, which were essential for a safe descent and ascent from the lunar surface. Without these systems, it would have been nearly impossible for the astronauts to land on the moon and return to Earth safely.

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