U.S. space agency NASA announced on Wednesday, March 25th that it had revised the plan for its Asteroid Redirect Mission (ARM), so instead of bringing a whole asteroid back into lunar orbit, a robot spacecraft will just grab a boulder off of an asteroid and bring it back.

NASA To Bring Asteroid Rock Back To Moon For Study

More on NASA’s Asteroid Redirect Mission

In the new ARM, an automated spacecraft will remove a boulder from the surface of an asteroid and transport it into a stable orbit around the moon in an initial step towards NASA’s planned manned journey to Mars.

The specific asteroid chosen for the mission will be announced no earlier than 2019, around a year before the launch of the mission. NASA has identified three possible asteroids for the mission so far: Itokawa, Bennu and 2008 EV5. Another one or two candidates are likely to be found each year leading up to the mission.

After reaching the asteroid that is chosen, the ARM spacecraft will use its robot arms to pick up a reasonably large boulder from its surface. The spacecraft will then start the long trip to redirect the space rock into a close orbit around the moon.

However, before the asteroid boulder is nudged into lunar orbit, NASA plans to test planetary defense techniques it has developed to deal with potential asteroid  impact threats. Experts say the experience acquired through this test will help the agency better understand its options to prevent an asteroid from hitting the Earth in the future.

Statement from NASA Associate Administrator

“The Asteroid Redirect Mission will provide an initial demonstration of several spaceflight capabilities we will need to send astronauts deeper into space, and eventually, to Mars,” noted NASA Associate Administrator Robert Lightfoot. “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.”

“We’re going to have a sensor suite on the spacecraft that will allow us to actually look at the boulders and actually make an educated choice about which ones we’re going to pull,” Lightfoot continued.

Solar Electric Propulsion (SEP)

The robotic spacecraft is designed to test various capabilities required for future manned missions, especially advanced Solar Electric Propulsion (SEP), a methiod for converting sunlight to electrical power and using the power to propel charged atoms to move a spacecraft. Space researchers note this method of propulsion is highly efficient and can move massive cargo around in space. Although much slower than chemical rocket propulsion, SEP spacecraft require much less propellant and fewer launches, factors which would significantly reduce costs on long manned missions.

Future SEP spacecraft could leave cargo depots or vehicles for future human missions in deep space, either close to Mars or around the moon as a waypoint for trips to Mars.

ARM’s SEP-propelled spacecraft is also planning to test new trajectory and navigation techniques, using the moon’s gravity to place the asteroid in a stable lunar orbit that makes it accessible for research. Mars mission planners are considering a similar staging point for astronauts to eventually rendezvous with a deep space habitat that would transport them to the Red Planet.