Plans outlined by President Obama in 2010 are beginning to come to fruition. The first stage of NASA's new deep space exploration directive will come in the form of wrangling an asteroid straight out of deep pace for detailed study near Earth. After capture by a yet-to-be-designed spacecraft (potentially something like the rendering in the image above), the asteroid will be towed to a stable orbit around the moon, where astronauts can visit the newly-domesticated space rock at their leisure.
That first manned visit is tentatively planned for the year 2021, but NASA has plenty to do before it sends up an asteroid drilling team. For starters, we need to identify a decent candidate asteroid. NASA's ideal match is a carbonaceous rock, approximately 23 feet in diameter, that contains water and other "volatiles." The size and makeup of the rock is important, not only in regard to the fields of study viable on suck an asteroid, but for safety reasons as well. A 23-foot asteroid would likely weigh about 500 tons. That's pretty hefty, but it's not large enough to pose any serious danger to humanity, even if it somehow struck our planet. And then we've got to figure out a way to grab the rock, get it over to the Moon, and put it into a stable orbit.
The mission in its entirety sounds like science fiction, but it's feasible with existing technology. Or so say scientists at Caltech's Keck Institute for Space Studies. Their calculations estimate that a mission of this complexity and magnitude would cost somewhere on the order of 2.6 billion dollars, which is about the same magnitude as the Mars Science Laboratory project. And that's before any astronauts get a shot at visiting the rock, but maybe by 2021, we'll be back at the Moon anyway.