Yet another in today's series of reposts of articles about space policy. This is another old blog post from 2004, back when the Moon-and-Mars plan was first announced. As with the previous posts, any numbers or links in the post may be badly out of date, and there are some good comments at the original post that are worth reading.
This installment contains my attempt at finding reasons why it wouldn't be completely idiotic to try to put a permanent base on the Moon. I'm not sure this was entirely successful, but it's worth a shot:
It's a little foolish to attempt to comment on the merits of Bush's new space proposal, which is still mostly vapor at this point. I haven't seen a clear breakdown of exactly what would be involved, and probably won't until it's officially announced this week, with slick charts and PowerPoint slides. Of course, refraining from comment on the basis of insufficient information would run counter to the whole blogging ethos, so I'll feel free to spout off. I should also note that this is the least well-founded portion of my commentary, consisting primarily of my own opinions and speculation, and drawing less on the comments of very smart people who actually know what they're talking about. Caveat lector, and all that.
I should also say that I tend to agree with those who say that the whole mission-to-Mars thing is completely ludicrous on financial grounds. We just don't have spare billions to start throwing at the space program, and gutting the rest of NASA to pay for it would be exceedingly stupid. This isn't a high priority at the moment, and any argument about whether the proposal makes sense as a whole starts and ends right there.
That said, it's still sort of interesting, in an academic way, to think about whether the mission as proposed makes sense from a technical standpoint. That's what I'll be talking about in what follows.
The skeleton of a plan that I've seen cited has three main elements: 1) Retire the Shuttle fleet, and replace it with a more Apollo-like "Crew Exploration Vehicle," capable of reaching orbit, or traveling to the Moon and back. 2) Start sending manned missions to the Moon and back, beginning with stays of a few days, and working up to a more permanent presence there. 3) Once a Moon base is set up, send manned missions to Mars, on the same sort of basis. The first element is relatively uncontroversial. There are people who think we should replace the Shuttle fleet with something more ambitious (space planes or space elevators), but basically nobody who would argue in favor of keeping the current system.
Technical objections to the plan center around the second step, with most people arguing that sending manned missions to the Moon is idiotic, and probably counterproductive. They tend to prefer either a bigger space station at the stable Lagrange point between the Earth and the Moon, or something like Robert Zubrin's "Mars Direct" plan, which involves sending robot missions to place supplies on Mars which would then be picked up by astronauts, and used for the return trip. There's some merit to these-- Zubrin's plan, in particular, has some really good points-- but I think that the Moon is not as idiotic a destination as most people think.
The objections to using the Moon as a starting point for a Mars mission all center on gravity. It takes a tremendous amount of money to lift anything out of Earth's gravity well, the argument goes, so why would you want to squander that by going to the Moon, which also has a gravity well (albeit a shallower one) to be overcome before you launch anything to Mars?
Gravity is actually one of the reasons why I think the Moon might make more sense, though. As anybody who follows the International Space Station program knows, building things in zero gravity has turned out to be an excruciatingly slow process. In part, this is because, as Bob Park noted in Congressional testimony, free fall turns out to be a very stressful environment for people to live in. There's also a Newton's Laws problem-- on Earth, you can rely on gravity to keep yourself in place while you move heavy objects around. In free fall, the Third Law will get you every time. Just unscrewing a few bolts turns into a huge ordeal, requiring careful bracing against big objects, lest reaction forces start you spinning.
Working on the Moon might alleviate those problems. The gravitational force on the Moon is less than on Earth, but it's still there, which ought to reduce the stress on humans working there (I don't think we have anywhere near enough data to know). And the combination of gravity and a solid place to stand might make construction projects go more quickly. The combination of those two things could easily be enough of an advantage to make the Moon a worthwhile starting point.
(There are other arguments that are sort of a wash, too. The Moon is resource-poor, lacking even an atmosphere, so you'd need to ship everything up from Earth. But that's going to be true anywhere you go, and the Moon isn't entirely useless-- after all, when it comes to building human habitats in space, it's hard to beat the radiation shielding properties of a meter or two of solid rock...)
There's a bigger reason why the Moon makes sense, though: you need to crawl before you can walk. Mars Direct is a wonderfully clever plan, but it suffers from the same arrogance of complexity that I mentioned in my last post. Zubrin's plan calls for advance teams of robots to land on Mars with a vehicle that can be used to return to Earth, a year's supply of food, and a reactor to make fuel and water from resources found on Mars.
It's a nice idea, and builds off NASA's experience with unmanned missions, but it's a huge gamble for a manned mission involving months of travel to get there and back. For the Mars Direct plan to work, lots of things needs to go smoothly-- the unmanned craft need to land safely, the food and tools need to arrive without damage, the assembly robots need to do their jobs correctly, and you've got to end up with enough usable fuel and water for the trip back. If any of those processes fail (keep in mind, we don't have a great track record with landing things on Mars safely), or anything unexpected happens (say, a severe wind storm (Mars does have weather) that damages some crucial component), the world gets treated to the spectacle of astronauts starving to death on CNN.
Elements of the plan are very good, particularly the idea of unmanned advance missions to put supplies in place. But this is the sort of project that demands extensive testing before lives are bet on it, and that's where the Moon comes in. We already know that it's possible to send manned missions to the Moon with enough supplies for the round trip, which gives you a safety net. Send the robot supply missions to the Moon, let them do their thing (you'll need to send along a few air tanks to simulate the Martian atmosphere, which the Moon lacks, but since they don't need to have enough fuel to get to Mars, that should be fine), and then send manned missions to pick the stuff up. If there's a problem, they can carry enough food and fuel with them to make it back, and in the absolute worst case, they're only a few days from Earth. If it does work, hey, you've got extra supplies in place to use for a Moon base. After it's worked a few times on the Moon, then try it on Mars.
(An even bigger problem with Zubrin's plan is that is sounds like a "proof of principle" sort of mission, that doesn't really lead anywhere. You can send men to Mars and back, and do science more efficiently there, but getting from there to permanent colonies still seems like a big stretch. He does claim to have a plan for that, too, but I don't care enough about it to buy his book and find out what it is, so I'll defer to people who've read it...)
If the goal of a manned space program is to eventually put permanent colonies on other planets, going back to the Moon seems like an eminently reasonable first step. Yes, there's nothing there that anybody wants (at least until helium-3 fusion becomes practical), and yes, a self-sufficient Moon colony would be extremely difficult to build and maintain. But it's a convenient place to test out a lot of techniques and technologies that would need to be used in more ambitious manned missions, and its relative closeness to Earth could provide the kind of safety net you need to avoid catastrophe.
Of course, there may be stronger arguments against going to the Moon than what I've heard-- for that, you'd need to consult actual rocket scientists. And again, there's a solid case to be made that this makes absolutely no financial sense at the present time. But as a purely academic exercise in imagination, it strikes me as not actually as terrible a plan as other commentators have claimed.