Closer encounter: Nasa plans landing on 40m-wide asteroid ...

traveling at 28,000mph

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The mission - the first to what officials call a Near Earth Object (NEO) - is being floated within the US space agency as a crucial stepping stone to future space exploration.

A report seen by the Guardian notes that by sending astronauts on a three-month journey to the hurtling asteroid, scientists believe they would learn more about the psychological effects of long-term missions and the risks of working in deep space, and it would allow astronauts to test kits to convert subsurface ice into drinking water, breathable oxygen and even hydrogen to top up rocket fuel. All of which would be invaluable before embarking on a two-year expedition to Mars.
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As well as giving space officials a taste of more complex missions, samples taken from the rock could help scientists understand more about the birth of the solar system and how best to defend against asteroids that veer into Earth's path.

"An asteroid will one day be on a collision course with Earth. Doesn't it make sense, after going to the moon, to start learning more about them? Our study shows it makes perfect sense to do this soon after going back to the moon," said Rob Landis, an engineer at Johnson Space Centre and co-author of the report, which is due to be published in the journal Acta Astronautica.
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A round trip to an asteroid could be done with less fuel than a moon mission, but is technically very challenging. The asteroid is only 40 metres across and spins as it hurtles through space at 28,000mph.

Landis thinks that a trip to an asteroid could capture imaginations even more than a return to our nearest celestial neighbour. "When we head back to the moon, I think we'll see many of the same scenes we saw in the 60s and 70s Apollo programme. We've been to the moon, we got that T-shirt back in 1969. But whenever we've sent robotic probes to look at asteroids, we've always been surprised at what we've seen," he said.
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http://www.guardian.co.uk/science/2008/may/07/starsgalaxiesandplanets.spaceexploration

The idea of an asteroid mission has been discussed here before. It looks like it's getting more and more serious attention. I think it's a very good idea for a manned mission, probably more important than a mission to Mars.