Talk:Descent propulsion system

RL-10

I just noted a couple of errors in this article relating to the Rocketdyne development. The pump-fed regeneratively cooled LOX/LH RL10 was not a contender for the DPS role. It was not manufactured by Rocketdyne, but rather Pratt & Whitney, which was not a part of Rocketdyne at that time. Rocketdyne's Descent Engine prototype was an ablatively cooled Aerozine-50/N2O4 engine like all of the other Apollo primary propulsion systems. It used a somewhat standard backplate hypergolic injector design like the smaller ascent engine, which was susceptible to combustion instability--the main challenge of rocket-engine design. It used helium injection as a throttling technique, which resulted in very low performance in low-thrust throttling. The TRW engine, with its pintle injector, on the other hand, was inherently stable, and demonstrated almost constant performance across its throttling range. Stability and performance were the reasons TRW's design was chosen. The decision was a NASA internal political battle, because James Web favored Rocketdyne for their experience (they were also a division of North American Aviation), whereas TRW had never built a major rocket engine before LEMDE. Its rocket-engineering team leadership mainly came from JPL. Beartham (talk) 21:53, 24 October 2013 (UTC)

Correct on all counts. I don't know why the RL-10 was even introduced in the first paragraph; the original version was not even throttleable. I've removed the incorrect info. JustinTime55 (talk) 14:50, 28 October 2013 (UTC)

This was a typo "RL-10" from my original submission, which should have been the Aerojet AJ-10 engine.

The AJ-10 had already been selected for Service Module, and its heritage goes back to the Vanguard program. Multiple publications (historical compilations, biographies, and technical articles) provide different viewpoints of the historical accounts.

Space Technology Laboratories (STL), a division of Ramo-Wooldridge Corp. had a long history with USAF development of America's ballistic missile program. This is covered in the biography of General Bernard Adolph Schriever. R-W became the main provider of system engineering and technical direction for the Air Force's Atlas ICBM. R-W's Guided Missile Research Division (GMRD) later expanded to provide system engineering for the Titan ICBM and Thor IRBM programs. After launch of Sputnik, GMRD was reorganized as a separate subsidiary corporation, the Space Technology Laboratory (STL), with Simon Ramo as president, Louis Dunn as executive vice president and general manager, and James H. (Jimmy) Doolittle as chairman of board of directors.

Chapter 12, Mike Gruntman's Blazing the Trail. The Early History of Spacecraft and Rocketry, AIAA, Reston, Va., 2004 Beatgr (talk) 13:15, 13 July 2014 (UTC)

WikiProject Spaceflight - importance rating

Here's what NASA's history pages say about the Descent Propulsion System: "The lunar module descent engine probably was the biggest challenge and the most outstanding technical development of Apollo." (quote from beginning of 5th paragraph)

It was the first pintle rocket engine, was the first throttleable engine for manned space flight, and was used to bring Apollo 13 home. It was adapted to the second stage (Delta-P) of the Delta launch vehicle for 77 launches without a failure.

The pintle engine design has been adopted by SpaceX in their Merlin engines to allow reuse of their boosters. Overjive (talk) 01:21, 2 July 2016 (UTC)

Why does the pressure rise

Development says "Pressure from the helium would gradually rise as the propellant tanks in the descent stage were depleted and eventually become high enough to rupture them" - This seems strange ? - Use of propellant would reduce the pressure ? Surely the pressure rises due to the helium warming up over time ? (Was it loaded as compressed gas or liquid ?) - Can someone correct or clarify ? - Rod57 (talk) 20:01, 20 January 2018 (UTC)

NASA Technical Note: October 24, 1972 says (p3-5) it used cryogenic supercritical helium loaded at 10° R (!) and stored at 3500 psi in "a highly thermally insulated pressure vessel. Pressure in the storage tank was allowed to rise because of the heat leak into the tank (approximately 8 to 10 Btu/hr)." - I'll reword and use that ref. - Rod57 (talk) 20:29, 20 January 2018 (UTC)

System pressure

TN D-7143 says

The initial concept of the DPS pres- surization system used helium stored in two high-pressure tanks with pressure control and supply components (fig. 2). Helium was to be stored at 4500 psia but later was changed to 3500 psia to optimize system weight.

Note well: The initial concept was to carry these high pressures. The supercritical helium system allowed this to be reduced. The helium tank would have had to be large enough to hold all the pressurant gas inventory, and thick enough to handle the pressure. I'm working from memory here, but I think the SHe tank burst disk was 1800 psi. I'll have to check the Apollo 13 info, where the disk actually burst. Anyway, what the article says is wrong, and I'll fix it when I figure out the right number.

As to the previous question about pressure rising, the SHe tank was loaded with liquid helium, but once sealed heat leaked through the insulation and warmed it up, above the critical point. As heat continued to leak in the helium got warmer, and the pressure rose. This was normal on the ground and on the way to the moon. Once they arrived at the moon the DPS was pressurized, helium was drawn from the SHe tank, and the pressure dropped. Once the engine was running, fuel was run through a heat exchanger in the SHe tank to keep the pressure UP, otherwise it would get too cold and unable to pressurize the propellant tanks.

On Apollo 13 the insulation was worse than usual for some reason. The pressure rise rate was quite a concern, and they were worried that the burst disk might go before they got to the moon and bled off pressure normally. This would have resulted in loss of mission because they would not have been able to maintain system pressure through the landing burn. They were even working on a procedure to do an early burn to try to bring the pressure down. Well, all that went into the wastebasket once the big problem started. The disk still burst late in the flight, after flying around the moon, but at that point they had enough pressure in the tanks for whatever was left of the mission.

Pgramsey (talk) 04:06, 17 October 2024 (UTC)

Thanks, Indefatigable, for fixing my clunky units conversion. Pgramsey (talk) 01:43, 18 October 2024 (UTC)