2015-10-22. NASA Calls for American Industry Ideas on ARM Spacecraft Development.
Source: NASA Release 15-213
Excerpt: ...NASA's ARRM [Asteroid Redirect Robotic Mission] spacecraft will need to be able to demonstrate support of high power solar electric propulsion, with initial solar array power of approximately 50 kilowatts. The robotics capture system planned aboard the pioneering vehicle will be capable of acquiring a 20 ton (or larger) boulder of up to about 19 feet (six meters) in width from an asteroid's surface and then returning it to an astronaut-accessible orbit near our moon. ...The spacecraft will need to be ready for launch by the end of 2020. ...While at a large asteroid, the spacecraft will demonstrate a "slow-push" planetary defense asteroid deflection technique during the mission. This uses the spacecraft and boulder's combined gravitational pull to attempt to change the course of an asteroid....
http://www.nasa.gov/press-release/nasa-calls-for-american-industry-ideas-on-arm-spacecraft-development