Massive 1-km wide asteroid set to fly by Earth on April 19

Nasa is planning ambitious mission that will see a robotic spaceship visit an asteroid to create an orbiting base for astronauts. The robot ship will pluck a large boulder off the space rock and sling it around the moon, becoming a destination to prepare for future human missions to Mars. Nasa plans to study the asteroid for about a year and test deflection techniques that one day may be necessary to save Earth from a potentially catastrophic collision. Although the target asteroid is not expected to be officially selected until 2020, NASA is using 2008 EV5 as the reference asteroid while the search continues for potential alternates. Before beginning its trip to lunar orbit, the ARM spacecraft will demonstrate a widely supported asteroid deflection technique called a gravity tractor.