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Asteroid redirect mission: impossible?


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Here’s my story, posted at midnight last night, about NASA’s new Grand Challenge, which is to find all the dangerous asteroids out there and figure out what to do about them. Basically the government wants help in finding near-Earth space rocks, and is turning to the global space community, including academics, backyard astronomers and other “citizen scientists.” A bunch of the top NASA officials took the stage in the auditorium at HQ this morning to discuss this new Grand Challenge and the much-hyped Asteroid Redirect Mission. NASA wants to capture a small asteroid and put it in a high orbit around the moon, then visit it with astronauts in the early 2020s. The problem is that, although there are untold thousands of near-Earth asteroids out there, few are astrodynamically attractive.

Gosh I love saying that, so let me say it again: Few are astrodynamically attractive.

Their orbits are too eccentric, or too hard to pin down, or they’re just going too dang fast relative to the Earth. This mission needs a rock that’s going less than 2km per second relative to the Earth. And it can’t be spinning too fast. And ideally it wouldn’t be a pile of rubble, but would be carbonaceous, a primordial rock from the birth of the solar system, and full of interesting clues about how the Earth formed and became habitable.

The small rocks needed for this mission (under 10 meters in diameter) are the hardest ones to see. You might get a glimpse of one, but at first glance it’s hard to know much about it, such as the spin rate and the composition and even the size (for that you need to know the albedo).

So as NASA asks for help in finding killer rocks it is also hoping to get some help in understanding the small-asteroid population out there as it continues to look for the perfect target for the redirect mission.

What we heard today is that there’s a potential variation on the redirect mission that would eliminate the problem of finding a small rock in the perfect orbit and with the perfect characteristics. Instead, a robotic craft could go to a known, big, well-understood asteroid, and break off a chunk. In fact, NASA already has a sample-return mission planned, called OSIRIS-REx, in which a spacecraft will obtain a small amount of material from the asteroid Bennu and return it to Earth. Presumably obtaining a sample from a well-characterized, easy-to-study, big asteroid would be easier than trying to latch onto a small, spinning rock of largely unknown characteristics. The robotic craft could then take the sample — which might be only a few feet across — back to lunar orbit to be visited by astronauts.

Of course, one might ask, gently, whether any of this will actually happen.

Stay tuned and I’ll try to answer that in the weeks ahead.




Joel Achenbach writes on science and politics for the Post's national desk and on the "Achenblog."



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Joel Achenbach · June 17, 2013

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