Chair Force Engineer

Tuesday, February 12, 2008

From the Moon to Mars

This week, dissident scientists and space explorers meet at Stanford to discuss alternatives to NASA's mission of sending humans to "The Moon, Mars and Beyond." The group seems to have coalesced around the position that the Moon is an unneeded detour on the road to Mars, and prefer manned asteroid missions as precursors to a human Mars mission.

As critical as I have been of NASA during the "ESAS period" of exploration, I think the agency's priorities are in the right place. While Mars offers more benefit than the moon in terms of both science and exploration, I think there is still much to be gained from the Moon. (This should come as a surprise to the people who knew me in my younger days, as I used to be a hardcore disciple of Bob Zubrin and his Mars-first agenda.) I also believe that asteroid missions are a worthwhile pursuit during Project Constellation, but they pose many challenges beyond the complexity of manned moon landings. The moon is in our own backyard, and it should be the first step in a logical plan of exploring the solar system.

When the Vision for Space Exploration was first rolled out in Early 2004, I recognized that a "Moon first" approach ran the risk of establishing a "lunar quagmire" that would prevent NASA from later flights to Mars. I didn't think that the "Lunar Quagmire" was inevitable, but I knew that NASA had to be smart about its lunar plans in order to avoid it. I could forsee two approaches for avoiding it:
1) Develop a lunar architecture with obvious applications to Mars in future development spirals
2) Deeply involve the private sector in lunar missions, so they can take over the lunar base when NASA has progressed to Mars

As Bob Mahoney notes in his recent The Space Review article, NASA has done a poor job demonstrating how the ESAS architecture could be extended to Mars. Not that it can't be done, mind you. SpaceWorks Engineering did a study showing how Ares I, Ares V and Orion could be used for human missions to Mars. Unfortunately, the SpaceWorks architecture comes with a steep price tag and a high pucker-factor. Still, the applicability of a heavy-lift rocket and capsule to Mars missions is a sound idea.

One of the ideas presented in ESAS that I was actually fond of was the use of methane and oxygen propellants for the Orion service module and Altair ascent stage. Unfortunately, methane propulsion was one of the first things thrown out of ESAS due to its long development time. But cryogenic methane and oxygen do have applicability to Mars (because they can be produced in-situ,) and they offer better performance than storable propellants. Unfortunately, NASA has been reluctant to address the problem of long-term cryogen storage in space, an unresolved issue that could pay off with huge dividends in the long term.

It remains to be seen if any of the Altair hardware is applicable to a Mars mission. There's a vast difference between a cabin that can support four astronauts for seven days on the moon, and one that can support at least three astronauts for nearly 600 days on Mars. Further, is there anything from the Altair ascent & descent stages that can be applied to a Mars lander or ascent craft? Probably not, especially if Methane & Oxygen propellants are produced on Mars.

In The Case for Mars, Bob Zubrin suggests that his "Mars Direct" architecture could be used with minimal changes to support moon missions. The logic behind this is a bit dubious, as safety would dictate the astronauts travel in a craft capable of both direct landing on the moon, and direct ascent from the lunar surface to earth. A heavy-lift rocket in the same class as Saturn V could only deliver a two-man, direct-ascent spacecraft to the moon.

While such an architecture would not be very mass-efficient, it does have some unique operational benefits. The descent stage of the manned lander could also be applied to a long-duration lunar habitat. Such a habitat would enable longer surface stays than the cabin launched as part of Altair. While only two crew would arrive initially, one or two more direct landers could drop off additional astronauts to man the lunar surface base. Further, the long-duration lunar habitat would retire a lot of the technical risk facing a Mars habitat.

Admittedly, I'm more a fan of L1 rendezvous for human lunar missions. I'd eventually like to see propellant production on the lunar surface, and reusable landers shuttling humans and cargo between an L1 station and the lunar surface habitat. While such a task should be left to the private sector, there's nothing stopping NASA from adopting L1 rendezvous for the first generation of Constellation missions.

Still, the use of direct landing and surface rendezvous deserves to be explored in greater detail. While an Ares I and Ares V might be able to launch four humans to the moon for seven days on the surface, two Ares V's could put two humans on the moon for a much longer span. For a fairly low marginal cost, a third Ares V could deliver two more humans to the same lunar surface base, establishing the same crew size as the baseline ESAS architecture (with significantly more time on the surface to explore and perform research.)

Many Americans look at the moon and think "Been there, done that." The public needs to see why a lunar return is worthy of their tax dollars. Tying it into the success of a Mars mission is an important part of NASA's public relations campaign (and an aspect that NASA has not handled well.) If NASA can't "sell" the idea that its architecture will help us get to Mars, it should look ahead and tweak it, in order to bring the Red Planet a little bit closer to our reach.