Son of Apollo
The next lunar lander will be a giant leap ahead of the first.
- By Tony Reichhardt
- Air & Space magazine, May 2006
Illustrations by Paul DiMare
(Page 4 of 8)
Mike Griffin, who became Administrator of NASA last year, was particularly eager to liberate the next generation of moonwalkers from lunar dust. So the Architecture team added an airlock, or dustlock, to the LSAM that will function like a mudroom in a suburban home -- a place where astronauts can remove their dirty things and avoid tracking the mess inside.
Airlocks have other advantages. With an airlock, the main cabin always stays pressurized, and the airlock acts as a transition zone between the shirtsleeve environment and the vacuum outside. Say all four astronauts are on a moonwalk and one suit develops a leak. Without an airlock, all four have to come inside at once and stay there, since any later entrance would expose the unprotected crewmember to the lunar vaccum.
The outer structure of the LSAM cabin will likely be a cylinder, similar to the large pressurized cans that make up the International Space Station's living and working spaces. The airlock could be a smaller, attached cylinder, though it needn't be.
In some designs, says Connolly, "we're talking about just putting an extra bulkhead and a hatch into [the LSAM] cylinder." But it might be preferable to have the airlock hatch closer to the lunar surface instead of placing it 15 or 20 feet off the ground, reachable only with a long ladder. The study team played with different options, including a kind of split-level design in which the astronauts descend a tunnel before heading out the airlock. The spacecraft's designers are still working to determine the exact configuration.
As for propulsion, NASA will go with the old reliable: liquid hydrogen/liquid oxygen engines for the descent stage, and hydrazine and nitrogen tetroxide for the ascent stage. The LSAM descent stage will use a modified version of the venerable RL10 engine, which entered service in 1963, just as Apollo was getting under way.
The descent engines for the lander have to be throttleable -- by the time of touchdown, they'll produce barely enough thrust to keep the vehicle from falling to the surface in the one-sixth gravity of the moon.
Today's RL10s can throttle down to 20 percent of their full thrust, but the LSAM engines will have to do better: 10 percent. That shouldn't pose a problem, thinks Connolly, but the achievement still requires some development work, and NASA may want to test these highly throttleable engines on robotic landers scheduled to begin visiting the moon as early as 2011.
Because the descent engines will be bigger and more powerful than the ones that flew on Apollo, engineers have had to consider the effects of the stronger blast on the lunar surface. When Pete Conrad piloted his lander to a touchdown in the Ocean of Storms during the November 1969 Apollo 12 mission, the rockets kicked up so much dust that for the last two minutes of his descent, he could hardly see anything below him. Could the debris from a more powerful blast fly up and hit the lander?