Nasa is giving the moon its own moon, to keep Earth safe from asteroid impacts and prepare for mission to Mars

The Asteroid Redirect Mission (ARM) will also allow Nasa to demonstrate many of the technologies that will carry humans to Mars. "The option to retrieve a boulder from an asteroid will have a direct impact on planning for future human missions to deep space and begin a new era of spaceflight," said Nasa associate administrator Robert Lightfoot.

The technology used could also help Nasa defend the planet from future asteroid impacts. During the mission, the agency will try out the techniques that it could use to throw an asteroid off course if it were coming towards Earth.

An astronaut, anchored to a foot restraint, prepares to investigate the asteroid boulder. Nasa refers to the robotic arm plan as “option B”, and was selected over another plan that would see an entire asteroid redirected. In the successful plan, a robotic arm will land on an asteroid big enough to have suitable boulders on it, and then throw one of those into orbit around the moon.

Nasa said that it will pick an asteroid no earlier than 2019, and will launch the spacecraft carrying the throwing robot about a year later. Nasa has identified three candidates already — and expects to find one or two more per year — all of which will be examined for their shape, size, orbit and other characteristics before they are chosen.

Once the boulder is secured, the Capture and Restraint System legs will provide a mechanical push off that will separate the boulder from the surface and provide an initial ascent without the use of thrusters to limit the amount of debris created When the asteroid is chosen, and the craft landed on it, robot arms will be deployed to grab a boulder. The unmanned ship will then send the boulder into orbit over a number of years.

The same technology could be used in future to save us from asteroids that are headed towards the earth. The robot could eventually defend the planet by using a technique called a “gravity tractor” — if it heads towards the asteroid, the robot’s gravity can throw off the course of an asteroid without touching it. That will work even better if the robot can successfully grab a boulder, giving it more mass and more gravitational pull.

The Asteroid Redirect Vehicle conducts one of the 1 km fly-bys that are used to characterize and image the asteroid with a resolution of up to 1 cm. The mission will also be testing out technologies for future missions into deep space.

The plan will make use of Solar Electric Propulsion, for instance, which allows spacecraft to convert sunlight into electric power and use that to move through space. Using that technique is less efficient than burning fuel, but means that space missions will need much less fuel and fewer launches, bringing down costs.

Microspine grippers on the end of the robotics arms are used to grasp and secure the boulder. The microspines use thousands of small spines to dig into the boulder and create a strong grip. An integrated drill will be used to provide final anchoring of the boulder to the capture mechanism That technology could eventually be used to send out cargo or vehicles to be picked up by astronauts on their way to Mars. Objects could be sent out into space to work as a waypoint, or be ready for humans when they arrive on the red planet.