Of the three competing methods for Lunar missions (Direct Flight, Earth Orbit Rendezvous, or Lunar Orbit Rendezvous), which method is NASA banking on for it's future Moonbase?
I know that most folks are going to say this is REALLY off topic, but I want to get a bit of discussion on this topic; it's quite near and dear to my geek heart, and I know that Space Exploration is a Geek Thing, too.
NASA has laid out plans this past week for a program that will ultimately result in a long term Moonbase on one of the two Lunar Poles, inhabited starting in the 2020 region with the base becoming habitable about 2024. As a person with long and deep interest in space (and a former NASA worker, but that's for other times), and someone who's wife's best friend growing up grew up to be an Honest To God Rocket Scientist (and D&D DM), I found it somewhat inspiring.
No word, of course, over whether we'll be storing nuclear waste on the far side of the moon, and of course it's a bit late for it's 1999 debut.
However, one of the missing pieces in this is HOW we're going back to the moon.
Back in the late 1950s and very early 1960s, there were three practical methods that were figured out that could be done in a decade (and return the astronaut(s) back to Earth; some of the earliest, but discarded, ideas left the astronauts stranded for up to years while return methods were being developed!):
Direct Flight - In principle, by far the simplest. Also, by far the most difficult to actually BUILD, and the least efficient in terms of energy (the NOVA rocket required would have been nearly twice as large as the Saturn V, the mightiest rocket ever successfully launched). A Single Stage To Lunar Landing And Return (ie., classic 1950s rocket ships) would be the extreme of this idea.
Earth Orbit Rendezvous (EOR) - In principle, the "safest" in that all the pieces of the moon shot are assembled in Earth Orbit, the astronauts then take their landing vehicle from Low Earth Orbit (LEO) to the moon's surface, then return to LEO, where they get in the reentry capsule. The difficulty with this is that it took multiple rockets to get the required material into space for one mission. Also, it was potentially expensive for energy, in that all the fuel needed to go from LEO to the Lunar Surface, then to return to LEO, was carried down to the surface.
Lunar Orbit Rendezvous (LOR) - A radical idea of having the reentry ship go to the moon and orbit; it would carry the required fuel for the Earth Return, with the lander only needing enough fuel to go to the lunar surface from lunar orbit and to return to lunar orbit. This could be done with one (feasible) rocket, and of course is what Apollo ultimately decided on. The lunar lander vehicle would be left in lunar orbit and discarded when the reentry vehicle and it's support equipment were sent back to the Earth.
Now, however, we have new options, and at least one new requirement:
We now have the International Space Station, and the Lunar Lander(s) will need to be reusable, not discarded, as the LEMs were.
There is NO practical reason for NASA to go back to the Direct Flight idea; the Orion vehicle will be the first NASA spacecraft that uses Solar Power (discounting the ISS and Skylab, which were STATIONS). While the Orion reentry capsule could form the basis for a major part of the eventual lunar lander, it's unlikely to be used "as is", as it's function would be better served with a more purpose built design. With that in mind, either EOR or LOR is again going to be the preferred method to get to the Moon. With NASA's requirements that Orion be (ultimately) a deep space vehicle, it appears that either LOR or a EOR/LOR combination will almost certainly be used.
With reusable Lunar Landers, NASA needs to consider, then where they will actually do the LOR part of the flight... ie., where do you park the landers in orbit? While it would be possible to park them on the lunar surface, and have them leave for a rendezvous in orbit when the approaching Orion vehicle gets to the moon, it might be better to leave them in a parking orbit (they could then be refueled TWICE in cycle; once on the Lunar Surface, once while in orbit) vice ONCE per cycle (meaning the lander can be smaller, and more efficient). But to refuel them, you need a refueling "rest stop" in Lunar Orbit, or Orion needs to have that capability. In other words, do we need a miniature Space Station orbiting the moon to park at?
Any such Lunar Orbiting Space Station would be little more than an emergency short term habitat, refueling station, and vehicle crew transfer facility. No science would be done there, and it would amount to little more than a giant Gas station in space, little more than four docking ports, two solar cells, and a few large storage tanks. With some commercial companies currently working on such mini-space stations, NASA might not even need to develop such a Lunar Orbiting Outpost (LOO) itself (and to our British readers... yeah, I get the joke that we're talking about a port-a-john in space).
In addition, Orion derived (and Progress derived) unmanned freighters could be built to shuttle supplies to such a mini-station. Potentially, ISS could also be used in this; current Progress and Orion derived unmanned freighters could easily supply ISS with the equipment destined for the LOO; "deep space" freighters using extremely efficient, but very slow, ion propulsion could then transfer supplies to the LOO, where they would be transferred to the lunar surface by one of the lunar landers. The "deep space freighters" could then return to the ISS for their own refueling and a new cargo.
One of the advantages with this approach? Future LEO capable spacecraft need only be able to reach the ISS to send material to the moon. Potentially, if NASA uses an Orion derived Crew Transfer vehicle to shuttle astronauts from ISS to LOO, it might be possible to book Virgin Galactic all the way to the moon with this method, and we'll actually have a workable long term infrastructure to support Lunar Operations, and even potential deep space asteroid rendezvous and Mars missions. Essentially, in the end, we would have reusable assets in place on every part of the journey except potentially the Earth Launch and Earth Reentry; that's a potentially HUGE cost savings.
How likely is this?
NASA has committed to finishing the ISS, but "finishing" the ISS does NOT necessarily include the required fuel storage that would be needed for this approach (they could easily be added, though, as the time comes closer). Orion is being designed to be at least partially cheaply reusable (and the costs of, for example, Soyuz is not prohibitive), while commercial interests are working toward fully reusable LEO capable craft capable of inexpensive orbital operations, which is a help. But a big commitment to infrastructure puts a lot of political capital on the table. We can DO it; it would be cheaper in the long run; but it's a commitment that extends some twenty years. That's a long time in politics. More likely is a revised pure LOR approach, with every supply ship being a one-use ship, and the Orion itself carrying the "refueling station" for lunar landers stuck on "E" on the gas gage in free orbit. It's more expensive in the long run, though.
So, what do you think are the possibilities of how NASA is ultimately going to do this? Please vote, and feel free to comment!