Engines had been tested on the ground, to be sure, but the propellants were so corrosive that every descent engine, ascent engine and CSM SPS engine that flew in space were pristine, and had never before been fired. Ever.
Was there ever a serious thought to testing just the ascent stage of the LM?
Partially fill tanks are big deal for launch integration
I have another, probably stupid, question. Why not to use just one engine? Both engines used same fuel and descent engine was 3x more powerful, so it could lift-off just fine. Plus, they could throttle it. It would save development costs and lunar module mass.
Quote from: Jim on 08/05/2009 06:53 pmPartially fill tanks are big deal for launch integrationWhy?
Quote from: Proponent on 08/06/2009 03:39 amQuote from: Jim on 08/05/2009 06:53 pmPartially fill tanks are big deal for launch integrationWhy?Slosh?
Quote from: SnowBars on 08/05/2009 07:47 pmI have another, probably stupid, question. Why not to use just one engine? Both engines used same fuel and descent engine was 3x more powerful, so it could lift-off just fine. Plus, they could throttle it. It would save development costs and lunar module mass.Reliability
Wow, yeah. A single engined LM would basically have no abort mode in case of engine failure during descent. That would be scary for mission planning. Although it would simplify the abort mode tree...
Plus, that single engine would have to successfully restart and safely run a second firing to get the astronauts off the surface.
First, to Jim -- I have read in any number of books (particularly, IIRC, "Chariots for Apollo" by Pellegrino and Stoff) that the LM descent and ascent engines were never acceptance-fired, that they could not be successfully refurbished after firing. 2. Also, that the LM and CSM propellants, once loaded, set a "last date" by which the mission must be flown, after which the lines, gaskets, etc., in the propellant system had to be completely refurbished. After having the hypergolics loaded, the spacecraft was only "good" on the pad for about a month before it would have to be taken down and the lines refurbished.
Quote from: mrbliss on 08/06/2009 02:53 pm... A single engined LM would basically have no abort mode in case of engine failure during descent.An ascent engine failure carried much of the same risk.
... A single engined LM would basically have no abort mode in case of engine failure during descent.
The CSM SPS engine had to do that [restart] for TEI.
Quote from: relyon on 08/06/2009 04:34 pmQuote from: mrbliss on 08/06/2009 02:53 pm... A single engined LM would basically have no abort mode in case of engine failure during descent.An ascent engine failure carried much of the same risk.But the ascent engine was particularly simple and reliable, which I believe is what Jim alluded to in his one-liner "Reliability" earlier in this thread. This simplicity was possible because, unlike the descent engine, the ascent engine did not need to be throttled.
Not to take this too far OT, but when Martin Caiden wrote "Marooned," the plot of which was triggered by the failure of the SPS engine to light -- despite all the best efforts of ground support, vendors and the astronauts to fix it -- Wally Schirra told him there was another method to get the thing to work that Caiden had overlooked, but he was going to keep it to himself so he could remain "one up" on the author. Never did find out what that was.
Quote from: Proponent on 08/07/2009 01:03 amQuote from: relyon on 08/06/2009 04:34 pmQuote from: mrbliss on 08/06/2009 02:53 pm... A single engined LM would basically have no abort mode in case of engine failure during descent.An ascent engine failure carried much of the same risk.But the ascent engine was particularly simple and reliable, which I believe is what Jim alluded to in his one-liner "Reliability" earlier in this thread. This simplicity was possible because, unlike the descent engine, the ascent engine did not need to be throttled.Or gimballed.
Jim, as far as whether Apollo hypergol engines were fired prior to flight, I don't have the time to go hunting through my library at the moment. I have run across this reference in more than one source, though. If it's not true, then multiple people documenting the Apollo era have the fact wrong.Do you (or Blackstar, or anyone else here) have any documentation of acceptance testing of Apollo flight DPS, APS or SPS engines? That would also settle the question... all I have to go on are multiple reports in mainstream Apollo books of a "fact" that some seminal source may have gotten wrong.It is true, though, that no LM DPS engine was ever fired *in flight* for its rated 12-plus-minute PDI lifetime prior to Apollo 11. I'm sure many engines were fired through PDI profiles in ground testing, but in flight? LM-5's DPS was the first.-the other Doug