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)