PICTURES: Asteroids and Near-Earth Objects
The study's asteroid, ideally measuring 7 meters across with a mass of 500,000 kilograms (550 tons), would be captured by a spacecraft using a deployable capture bag (pictured top). Once secured, the spacecraft would steer the mass toward a region of gravitational stability known as the Earth-moon Lagrangian (EML2) point. This gravitational "island" has also been eyed as the potential location for a lunar farside space station - if you can park an asteroid there, a manned outpost could even use resources on a captured asteroid to sustain a station or act as a mining staging post, theoretically.
With the asteroid locked in its gravitational parking lot, NASA will launch a manned expedition to the tamed asteroid, allowing unlimited access to a scientifically bountiful objective.
Before the Keck plan, it was estimated that a 2025 asteroid rendezvous mission could take up to a year to complete; the Keck proposal would slash the human mission duration to weeks or even days. It would also be safer for the human crew and much cheaper - coming in at an estimated total cost of $2.65 billion. The Orion crew vehicle, that is currently undergoing development, launched atop NASA's next-generation Space Launch System (SLS), would provide the astronaut "shuttle service" to the asteroid. (The cost of developing Orion and SLS are a part of a separate allocation of NASA funds.)