Originally posted by JOEMA:
Quote:
Originally Posted by MG23
"It was basically designed to minimize the risk of failure, rather than to have backups if it did fail. The ascent stage engine, for example, was about as simple as you can make a rocket engine; if I remember correctly, it was pressure-fed and hypergolic, so just a couple of tanks, a couple of valves, and a rocket nozzle."
That is correct, and I would not describe the LM as lacking contingencies. The design philosophy was extreme reliability through simplicity -- even at a significant cost of performance.
One of the most interesting things I learned from reading about Apollo 13 was that NASA's design philosophy assumed that structures didn't - or wouldn't - fail. So structures, unlike systems, generally did not have backups or much redundancy. The reason was simple - the weight penalty would have been prohibitive. So they designed the structures and non-redundant systems to be a simple as possible.
There were multiple navigation systems on both the CSM and the LM, and multiple sources of electrical power on both as well. But there was only one SPS engine (albeit with two sets of valves for the hypergolic fuels) and only one descent engine and ascent engine on the LM.
They also tried to design the systems so that they could use what redundancy was inherent - being able to use the LM engine to power the entire stack, for example, as was done in Apollo 13, or more broadly being able to use the LM as a lifeboat for those portions of the mission when it was attached. But that fell well short of full redundancy. If the O2 tank on Apollo 13 had exploded when the LM was on the moon, or on return to earth, it would have caused the loss of the crew.