Separating the new lunar module into pieces will be even more important in 2018 than it was in 1969, when NASA's goal was just to land astronauts on the moon and bring them back safely.
This time, the missions are only prep work for something far more ambitious-a lunar outpost where small crews will live for up to six months at a time. The early missions will likely all land in the same location, incrementally adding descent stages and other hardware that will become the building blocks for the new base.
One piece that will be especially useful to leave on the moon is the LSAM's airlock, which represents one of the most significant improvements over the Apollo LM. The moonwalkers of the 1960s struggled with the fine, powdery dust that covered their spacesuits. Back inside their tiny one-room cabin, it got everywhere-in the machinery, in their eyes, in their throats.
Scott said that moon dust even got in the connectors between the backpack and the spacesuits."You could almost hear them grind after three days," he said. He ranks dust as "the major problem for a long stay."
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.