The original Apollo 8 mission, the E mission profile, would have flown as Apollo 9. As it flew as Apollo 8 as a C prime mission without a lunar module, then I assume LM4 went to Apollo 10, LM 5 to Apollo 11. Somewhere, there should have been a spare LM. When Apollo 15 H mission was cancelled, the CSM CSM-111, flew on the ASTP. The LM LM-9 is a museum piece at KSC. Since Apollo 8 should have had a LM associated for it, I assume somewhere in 1968-69 a LM order was cancelled. Does anyone know if and when NASA cancelled a LM order?
Quote from: Steve G on 04/23/2018 04:45 pmThe original Apollo 8 mission, the E mission profile, would have flown as Apollo 9. As it flew as Apollo 8 as a C prime mission without a lunar module, then I assume LM4 went to Apollo 10, LM 5 to Apollo 11. Somewhere, there should have been a spare LM. When Apollo 15 H mission was cancelled, the CSM CSM-111, flew on the ASTP. The LM LM-9 is a museum piece at KSC. Since Apollo 8 should have had a LM associated for it, I assume somewhere in 1968-69 a LM order was cancelled. Does anyone know if and when NASA cancelled a LM order? They all skipped to the next mission. If Apollo 8 had a LM, it would have been LM-3. We don't know what would have happened to LM-8 & 9, if Apollo 8 had LM-3LM-2 is at NASM, but it was never going to fly manned.
As is well-known, Apollo 8 was originally supposed to be a HEO test of the combined command and lunar modules, but this was dropped as being unnecessary, and then quickly converted to a solo CSM flight to lunar orbit.This was a pretty big gamble to go to the Moon with just the CSM, because even well before Apollo 13, NASA were conscious of the need to have the LM along as a backup spacecraft if the CSM malfunctioned. One of the big reasons for the flight was worry about what the Soviet space program might be doing and how many manned circumlunar missions they might have up their sleeve. Nobody knew of course just how behind and totally disorganized the Soviet manned program was in 1968, and even the Soviets themselves were surprised that we'd attempt Apollo 8 without a prior unmanned test flight. Frank Borman states in his memoirs that the decision for a solo CSM lunar mission was not made until August 1968.That also doesn't include the fact that the Saturn V was being committed to a manned flight after just two tests, one of which had some rather serious problems, or that the Apollo CSM itself was only on its second manned flight and was still something of a question mark. In regards to the second point, the hardware on Apollo 7 had performed almost flawlessly--the SPS and RCS systems were given an extensive workout and passed these tests with flying colors (in fact the crew were the only part of Apollo 7 that left something to be desired). This gave NASA sufficient confidence that the CSM was man-rated and could be trusted for Apollo 8's mission. If there had been problems on 7, then 8 would have flown another Earth orbital CSM test.The SPS was considered pretty much failsafe anyway; in the entire Apollo program, only two SPS malfunctions occurred--on AS-201, the very first test of an Apollo CSM, and on Apollo 16, and neither was serious enough to prevent the main mission goals from being achieved.
Also, I will point out that AS-201 had the only major in-flight issues with the SPS itself, during which it failed to develop full thrust (due to helium ingestion issues, IIRC.
Quote from: the_other_Doug on 04/24/2018 02:48 pmAlso, I will point out that AS-201 had the only major in-flight issues with the SPS itself, during which it failed to develop full thrust (due to helium ingestion issues, IIRC.But that was the first flight of a CSM, so that was ok. Any maiden flight of a new vehicle is going to have a few problems, it's more surprising if it doesn't.The helium ingestion was due to a broken piece of plumbing that allowed helium to enter the oxidizer line and cause a 30% drop in engine performance 80 seconds into the SPS burn. A second burn, lasting 10 seconds, resulted in unstable combustion, dropping to as low as 12%. Lucky this was a pressure-fed engine because on a turbopump engine, helium entering the fuel system would cause pump cavitation and end pretty badly.
Yep, that's one reason why pressure-fed engines were chosen for the major Apollo spacecraft engine systems. Turbopumps can fail, and often have Bad Day results when they do. Like, you thought Apollo 13's SM looked ripped up? You ain't seen nuthin'
That plus boil-off concerns was also one of the reasons why repeated suggestions, when looking at the Apollo mission mode, to use pump-fed hydrolox engines for LOI, descent and TEI were ignored. Hydrolox for those maneuvers would have made a Direct Ascent mode semi-feasible, even with just a Saturn V launcher. But it contained too many catastrophic failure modes (especially turbopump failure modes) for comfort, and hydrogen boil-off over the week or more it would have been happening was, and remains, beyond engineering capabilities.