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Here we are, nearly eight years into the 21st century, and the most spectacular manned mission NASA can pull off is a trip to the International Space Station, a mere 210 miles above the Earth. Even the most ambitious part of NASA's current plans for human spaceflight involves visiting a celestial body we've already been to: the moon. Astronauts, space buffs and an unimpressed public hunger for space exploration that's more dramatic, more heroic, more new. Something like, say, landing astronauts on a distant rock hurtling through space at 15 miles per second.
That's exactly the kind of trip NASA has been studying. In fact, scientists at the space agency recently determined that a manned mission to a near-Earth asteroid would be possible using technology being developed today. The mission wouldn't be easy. A crew of two or three would spend months riding in a cramped spacecraft before reaching their barren, nearly gravity-free target. That such a mission is even being considered, though, says a lot about the versatility of NASA's next fleet of spacecraft and the ambitions the agency has for them. If nothing else, it's a signal that space exploration could soon get much more exciting.
The Allure of an Asteroid
This wouldn't be our first trip to an asteroid. We've been visiting them by proxy for years now, using unmanned space probes. In 2000 NASA's NEAR Shoemaker spacecraft arrived at 433 Eros, which a century earlier became the first near-Earth asteroid known to man; five years later, the Japanese Hayabusa probe touched down on asteroid 25143 Itokawa.
Yet unmanned probes have their limitations. NEAR Shoemaker and Hayabusa gathered a good deal of data, but we still don't know the exact composition and internal structure of the asteroids they visited. And although Hayabusa was designed to collect two small samples from Itokawa, it's doubtful the probe will actually have anything onboard when it returns in 2010.
Humans, however, could be much more effective. Unlike robots, we adapt to our environment in real time. "We spend weeks at a rock with a Mars rover, trying to determine what it is," says Rob Landis, an engineer at NASA's Johnson Space Center and one of the co-leaders of the mission feasibility study. "An astronaut could make that determination in a matter of seconds."
A human crew could travel across an asteroid more intelligently than a robot, making it easier to deploy scientific instruments, collect samples, and zero in on the areas of greatest interest. "No doubt, on a human mission we would characterize an asteroid better than we ever have," says Bruce Betts, director of projects for the Planetary Society.
Plenty of characterization needs to be done. While most asteroids are a safe distance from Earth (in an approximately 190-million-mile-wide expanse between Mars and Jupiter), Jupiter's gravitational tug and, less often, collisions between asteroids can kick these objects into orbits that pass uncomfortably close to Earth. The 270-meter-wide asteroid 99942 Apophis, for example, will pass within roughly 24,000 miles of Earth in 2029, and could come back for a direct hit in 2036.
And if we're to have any hope of deflecting asteroids, we need to know a lot more about them than we do now. First off: What, exactly, are they made of? Measurements taken by Hayabusa indicate that 40 percent of Itokawa's volume is empty space. If some asteroids are truly this porous, that's helpful information for any plan to destroy or deflect an Earth-bound object.
Averting the apocalypse isn't the only reason to study near-Earth asteroids, though. They could be floating gold mines for future deep-space expeditions. Preliminary observations suggest that some asteroids are rich in useful minerals and, better yet, frozen water-the most valuable resource a space traveler could hope to find. If water could be extracted from asteroids, it could not only be used for drinking, but also broken down into oxygen for breathing and hydrogen for rocket fuel. "It might be an ultimate way to get to Mars," Landis says.