Chair Force Engineer

Thursday, June 22, 2006


NASA's Lunar Surface Access Module (LSAM) is at a very embryonic stage, but important design decisions are being made right now that will have serious ramifications when humans return to the moon. The new lander will be much more capable than the Apollo Lunar Module. Yet this additional capability will come at the expense of features that made Apollo's LM so reliable in the first place.

The biggest change with the LSAM is that it will use cryogenic fuels, at least in the descent stage. Apollo used low-energy, storable propellants. LSAM will have the propulsive capability to visit a variety of sites on the moon, while the Apollo LM had to stay near the equator. LSAM will also carry enough equipment to sustain a four-man crew for over a week, while the LM could only support two men for a few days.

The baseline for LSAM's descent stage is hydrogen and oxygen propellants, burning in four RL-10 series engines. RL-10 has had an enviable history. It has also been used in a similar application, in the DC-X reusable rocket (where the four RL-10A-5's were throttled down to 30% thrust for landing.)

Nevertheless, the RL-10 is not going to be smooth sailing for the LSAM. The descent and ascent engines on the old LM used hypergolic propellants and a reliable pintle-injector design, because the engine would be certain to ignite upon the opening of a redundant set of valves. In the RL-10 based LSAM, the astronauts will have to rely on four RL-10's igniting properly.

Storage of the cryogenic hydrogen and oxygen, and ensuring that they do not boil away during the transit to the moon, will also be a challenge. To that end, NASA plans on using hydrogen and oxygen propellants for the unmanned landers that will precede the LSAM. Another problem will be the loading of the propellants. It's unlikely that the LSAM will be fueled prior to encapsulation inside the Cargo Launch Vehicle's fairing. The most likely scenario is some sort of fuel port on LSAM that can be accessed through a door on the fairing, which will allow LSAM to be fueled along with the CaLV while on the launch pad.

I think Pete Conrad would be ecstatic knowing that the DC-X he worked on would be contributing to the lunar return mission. But I think that Grumman's LM project engineer, Tom Kelly, would be disappointed in knowing that so much of what his team pioneered would be cast aside.