The Asteroid Redirection Mission or ARM involves returning an asteroid to an orbit close enough to Earth that it could easily be studied by a manned mission. NASA somehow thinks getting hold of an entire asteroid isn’t a good idea. Hence it will place a robotic probe that will pluck a boulder from the surface of an asteroid and return that instead
NASA hope to test its ability to redirect similar rocks if they threaten Earth using the data obtained from ARM. In fact, the entire mission is generally focused on technology development. Once the asteroid is placed in a cis-lunar orbit (orbiting Earth and closer than the Moon), it will then be visited by a manned Orion capsule. The team on board will collect samples and bring them back to earth for detailed studies.
The Plan B of sorts, will have to be highly selective and would have to first zero-in on asteroids big enough to have boulders on its surface and then using robotic grapples, will have lift those boulders and somehow put it in precise and stable orbit around the moon. Option A however, wasn’t that simple ether. It involved finding a suitable asteroid less than 10 meters in diameter for redirection.
NASA strongly maintains that the focus of this mission will be testing technology that will eventually allow extended manned missions in space. However, the current timeline involves further studies of potential targets for extracting a boulder in the years leading up to 2019.
Interestingly, NASA has already selected a few suitable candidates who could donate a boulder: Itokawa (which was visited by the Japanese spacecraft Hayabusa), Bennu (which is planned for a sample return mission called OSIRIS-REx), and 2008 EV5. Their candidacy has been bolstered by the fact that their orbit and composition are well-known, making them relatively low risk.
[Image Credit | NASA]