Lunar Landing Engine Blueprint

[YourEverydayWaffle]

You guys'll probably appreciate this. I went to a sort of open seminar at MIT (no, I don't go there) on the basic physics of space and rockets. IT was pretty cool, but coolest was this: the woman teaching it had a huge photocopy of the original blueprint for the Apollo lunar landing engine (might not have been the lander engine, but was certainly planned to be part of the Apollo missions). Even cooler was that it was at a 1:1 scale. Here's some pictures (my camera isn't great, the lines are a bit light in these shots)

It was around 6-8 feet long (this was just the combustion chamber and the de Laval nozzle)

You can see where the dimensions and measurements were scribbled out and changed here, where the combustion chamber ends and the nozzle begins:

A little Bell Aerospace "certificate" in the corner, sort of like a signature, except with labels and specs.

Just sort of a cool thing to see when you're into this kind of stuff like me!

[Javster]

Great! (10char)

[rdfox]

Based on the contractor that designed it and the model number, this would presumably be the Lunar Module's Ascent Propulsion System engine--the engine used to leave the lunar surface and return to orbit. According to Wikipedia, the APS engine was actually derived from the main engine (Bell 8247) used in the Agena upper stage (famously converted into a docking target and orbital maneuvering stage for the Gemini program), with an emphasis on 100% reliability through simplicity (because if it didn't work, two men would be left on the lunar surface to die).

As a result, it was one of the two simplest liquid-fuel rocket engines ever flown (the other being the Service Propulsion System used on the Apollo Service Module, which needed the same reliability--because if it didn't fire, the crew would be stuck in lunar orbit for all eternity). It was pressure-fed rather than using any form of pump, it relied on gravity feed (if the Descent Propulsion System failed in a way requiring an abort from a free-fall, the RCS thruster quads would be used to provide ullage for startup), it used hypergolic propellants (which were so corrosive that it required a complete rebuild after each firing, so each lunar liftoff was with an engine that had never been tested) that required no ignition system to start the burn, and it had exactly TWO moving parts--one simple ball valve for each propellant, with two positions, open and closed. No throttle, no gimbal, no nothin'. If the valves failed to open, the astronauts could, at least theoretically, take the engine cover off inside the LM and manually open the valves to fire the engine. (This, mercifully, was never tested in flight!)

For the record, all steering of the LM Ascent Stage was done through the RCS, since the APS had no thrust-vectoring capability (because gimbals can break). It meant a less-efficient gravity turn profile, since it wasn't quite as smooth a turn, but it was felt that the reliability was more important than squeezing an extra 10 m/s or so of delta-V out of the vehicle. The SPS, by comparison, did have pitch and yaw gimbals, doubling the moving parts count (to four!) over the APS, because when it was designed (as an ascent engine for the entire Apollo CSM during the "direct-ascent or EOR" days), it was felt that thrust vectoring would be critical to its mission, while the SM's RCS thruster quads had enough control authority to be able to cancel the torque if a gimbal locked hard over on the SPS, allowing the burn to be completed anyway.

Further historical note: the APS engine was revived as the RS-18 in early studies for the Constellation program's lander, not intended as an actual flight engine, but instead with a stored APS engine restored and converted to run on methane/oxygen as a study/development engine for that propellant combination; the SPS, with a shorter nozzle, went on to be a very widely used upper stage engine for expendable boosters, and, in another variant, the OMS engine for the Space Shuttle. (The OMS variant was something the engineers were particularly proud of; of the initial batch of actual flight articles, only *four* ever had to be taken off the flight roster--the two lost with the Challenger, and the two lost with the Columbia. They were just that bulletproof reliable; all you had to do to turn them around was clean 'em out, reline the tanks and propellant lines, and they're ready to fly again, with seemingly unlimited lifespan...)

[YourEverydayWaffle]

Based on the contractor that designed it and the model number, this would presumably be the Lunar Module's Ascent Propulsion System engine--the engine used to leave the lunar surface and return to orbit. According to Wikipedia, the APS engine was actually derived from the main engine (Bell 8247) used in the Agena upper stage (famously converted into a docking target and orbital maneuvering stage for the Gemini program), with an emphasis on 100% reliability through simplicity (because if it didn't work, two men would be left on the lunar surface to die).

As a result, it was one of the two simplest liquid-fuel rocket engines ever flown (the other being the Service Propulsion System used on the Apollo Service Module, which needed the same reliability--because if it didn't fire, the crew would be stuck in lunar orbit for all eternity). It was pressure-fed rather than using any form of pump, it relied on gravity feed (if the Descent Propulsion System failed in a way requiring an abort from a free-fall, the RCS thruster quads would be used to provide ullage for startup), it used hypergolic propellants (which were so corrosive that it required a complete rebuild after each firing, so each lunar liftoff was with an engine that had never been tested) that required no ignition system to start the burn, and it had exactly TWO moving parts--one simple ball valve for each propellant, with two positions, open and closed. No throttle, no gimbal, no nothin'. If the valves failed to open, the astronauts could, at least theoretically, take the engine cover off inside the LM and manually open the valves to fire the engine. (This, mercifully, was never tested in flight!)

For the record, all steering of the LM Ascent Stage was done through the RCS, since the APS had no thrust-vectoring capability (because gimbals can break). It meant a less-efficient gravity turn profile, since it wasn't quite as smooth a turn, but it was felt that the reliability was more important than squeezing an extra 10 m/s or so of delta-V out of the vehicle. The SPS, by comparison, did have pitch and yaw gimbals, doubling the moving parts count (to four!) over the APS, because when it was designed (as an ascent engine for the entire Apollo CSM during the "direct-ascent or EOR" days), it was felt that thrust vectoring would be critical to its mission, while the SM's RCS thruster quads had enough control authority to be able to cancel the torque if a gimbal locked hard over on the SPS, allowing the burn to be completed anyway.

Further historical note: the APS engine was revived as the RS-18 in early studies for the Constellation program's lander, not intended as an actual flight engine, but instead with a stored APS engine restored and converted to run on methane/oxygen as a study/development engine for that propellant combination; the SPS, with a shorter nozzle, went on to be a very widely used upper stage engine for expendable boosters, and, in another variant, the OMS engine for the Space Shuttle. (The OMS variant was something the engineers were particularly proud of; of the initial batch of actual flight articles, only *four* ever had to be taken off the flight roster--the two lost with the Challenger, and the two lost with the Columbia. They were just that bulletproof reliable; all you had to do to turn them around was clean 'em out, reline the tanks and propellant lines, and they're ready to fly again, with seemingly unlimited lifespan...)

WOW. I would have never known! This is really cool to see, now I know so much about the blueprints I saw. Thanks!