Chair Force Engineer

Monday, November 12, 2007

Blind Ambition and Heavy Landers

When NASA performed its 2005 trade studies for the lunar mission, it assumed a crew of four astronauts would spend seven days on the lunar surface. I have not seen any justifications for this requirement, and I must say that it seems very arbitrary. Nonetheless, the lunar crew and duration requirements are having serious impacts on Project Constellation.

During Project Apollo, the Lunar Module weighed in at approximately 15 metric tons, and the Apollo CSM was roughly 30 metric tons. The Lunar Module was designed for little more than six man-days (two crew for three days.) Project Constellation reverses the paradigm: the Orion CSM is around 22 metric tons, while the LSAM is budgeted for 47 metric tons. The LSAM will support 28 man-days of lunar surface operations (four crew for seven days.) The LSAM is also expected to perform the lunar orbit insertion burn, which was performed by the Apollo CSM the first time around. (If the Orion CSM performed the LOI burn, it's likely that it would be too heavy to fit on the Ares I launcher.)

The problem with the current scenario is that LSAM is outgrowing its 47 mT budget, around which the Ares V and EDS were designed. One of the figures I've heard was a 55 mT LSAM, although I haven't seen enough evidence to confirm. In any case, NASA may be forced to slim down the LSAM by reducing the crew size, the mission duration, or both.

In a larger sense, we should probably be asking whether the mission requirements for Project Constellation are a bridge too far. NASA expects all the provisions for a long-duration lunar stay to arrive with the LSAM on a single Ares V. But Project Apollo, had it continued, would have relied on vehicles like the LM Shelter and LM Truck to extend the basic capabilities of the Apollo LM. Each of these vehicles would be delivered by an additional Saturn V launch.

A good analogy for the situation is that LSAM is a Winnebago, while the Apollo LM was a compact car. While you can't live out of the compact car for a significant period of time, you can always have a second sports car drive out and deliver a tent, food, and provisions for a longer stay. Having the Winnebago might be convenient, but the upfront costs are steep. NASA is re-learning this lesson the hard way. One one step, we are trying to eclipse Apollo. It might make more sense to duplicate Apollo, then build upon it in subsequent spirals.