Thursday, September 29, 2005

science vs engineering on the moon

There's a bunch of upheaval going on right now in the space community (NASA, non-government space companies, and advocacy groups). As has been widely reported, Pres. Bush and NASA have decided on a plan to push towards human exploration of the moon and Mars, replacing the space shuttle with a more traditional-looking, cheaper, and simpler set of expendible boosters. In addition, with the beginnings of space tourism just around the corner, several credible private companies have stated their intentions to build rockets capable of sending people into orbit as well.

But the real point of this article is to talk about the conflicting goals of human space travel beyond Earth's orbit. Pres. Kennedy said we should go to the moon not because it was easy, but because it was hard. That's a technological goal -- to develop the ability to do a seemingly impossible task. But the International Space Station was developed for a scientific mission -- to study the basic science of materials and people in zero-G. (Not that it'll be able to to much of that given how stripped-down it's going to end up.)

So the question is, why are we going to the moon? To do science? To develop and test the technology required to go to Mars? Because we're the richest country in the world?

There's not a lot of critical lunar science left to do. We sent a bunch of people there in the '70s, including one actual geologist, and brought back a bunch of rocks. It's fairly well understood what the moon's made of and how it's formed. The new program will very likely put people near the South lunar pole, where there might be water ice in shadowed craters, but that's about the only really important mystery remaining. (And mostly because it would be convenient to have ice around if we wanted to establish a base there.)

Although some of the technology required to go to Mars could be tested on the moon, a lot of it couldn't. In particular, the technology to generate rocket fuel out of the Martian atmosphere, which is basically required to get the people back, can only be tested on Mars. And that's one of the biggest challenges. Building structures on the moon isn't, well, rocket science.

And what about patriotism? Well, it's certainly true that China's talking about putting people on the moon. 7 years after John Glenn's orbital flight, Neil Armstrong and Buzz Aldrin landed on the moon. China's second orbital flight is expected in the next month or so. Some people are worried.

The stated purpose of the new lunar program is to develop technology and to be inspirational. A recent commentary in Nature expressed anxiety about this, saying that science has been neglected. I'm not so sure what the right rationale should be. To me, the most interesting stuff in astronomy right now is not on the moon, but planets around other stars. Perhaps the scientific goal of a moon base should be to establish really fantastic telescopes?

Unlike on the Earth, where there's clouds, rain, a shimmering atmosphere, and glare, telescopes on the moon could operate constantly. Orbital telescopes like the Hubble and its follow-ons are great, but they have comparatively small mirrors. One of the next steps in orbital telescopes is to develop fleets of telescopes and use them to combine their images for amazing resolution. (They do this on the ground fairly well, now.) The only problem is that you need to keep the telescopes from drifting more than, oh, a nanometer or two, and that's really, really hard. But if you put these telescopes on the moon, they won't drift. So what do you get? Well, you get a big array of telescopes able to resolve extremely small objects (like planets around other stars), not susceptible to interference from weather or the atmosphere. Plus, you can have the people at the lunar base go out and wiggle the wires if there's a problem.

My intuition is that people think astrobiology is really cool, way more so than studying the ionosphere of the outer planets or how people's blood pressure changes in zero-G. In my opinion, NASA's best hope of keeping public support is to continue to do really cool things, and to sell them as really cool things. Like build amazing little robots, and put people on the moon, and send them to Mars, and build telescopes that show us planets around other stars.

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