NASA’s next human-led expedition isn’t going to Mars. Think much, much smaller.

Nearly a decade before the first humans travel to the red planet, astronauts will head to a 3-meter “boulder” put into orbit around the moon by a robot.

The most exciting part isn’t humanity’s triumphant return to the Earth’s natural satellite, it’s how that boulder is going to end up in lunar orbit and what that means for our ability to protect Earth from asteroids.

What is the Asteroid Redirect Mission?

Launching in 2021, the Asteroid Redirect Mission begins by sending an unmanned spacecraft to an asteroid 400 meters in diameter and 64 million miles away, pluck a much smaller rock from its surface using robotic arms and then fly slowly to the moon for four to five years.

After the robot reaches its destination, astronauts will meet up with the robot and boulder, study it and collect samples to return to Earth.

“We call it one mission, but it is really a five-year robotic mission and a 25 or so day human mission,” said Brian Muirhead, project manager for robotic side at NASA’s Jet Propulsion Laboratory in La Cañada Flintridge. “We have never done anything like this before.”

While the Jet Propulsion Laboratory leads the robotic mission, six other NASA facilities are collaborating on the redirect mission.

The Asteroid Redirect Mission not only demonstrates technology for future missions, it also increases our ability to deflect asteroids that could smash into the Earth. The mission also likely sets the stage for future commercial mining of asteroid belts.

Among the technology that NASA is testing is its ability to move massive payloads across space using a solar-powered electric propulsion system.

Ion propulsion — which creates thrust from electricity — has only been used on smaller spacecraft. While it is much slower than traditional propellants, it lasts longer and weighs less.

If ion propulsion were used on large solar-propelled spacecraft, they could deliver habitats or return vehicles to Mars months and years ahead of human explorers in the 2030s.

“It’s an important first step for us on the Journey to Mars,” said NASA Administrator Charles Bolden at a press conference Wednesday. “It is going to give us an opportunity to sit out in the proving ground and make sure we understand the kind of things we need to do when we send our astronauts to Mars.”

But, how will the Asteroid Redirect Mission protect our planet from asteroids?

The unmanned spacecraft launched in 2021 will more than double its weight to 25 tons after gripping onto the boulder with a technology that mimics the feet of a gecko.

After leaving the asteroid, the spacecraft will use the added weight to act as a “gravity tractor” to shift the asteroid ever so slightly off course. The idea is that the gravitational force of the spacecraft and boulder will pull on the larger asteroid enough to change its trajectory. Muirhead stressed the change will be miniscule enough not to threaten Earth, but scientists will be able to detect the difference when the asteroid next flies by our planet.

NASA and the White House see the technique as a possible way to deflect a hazardous objects hurdling toward Earth.

The United States is already investing in asteroid detection.

“We’ve had some recent experiences that indicate how challenging this is,” said John Holdren, of the White House’s Office of Science and Technology Policy. “In 2013, a smallish asteroid exploded over Siberia with the force of about 400 kilotons or 500 kilotons of TNT, did a lot of damage on the ground, something like 1,000 people were injured by flying glass. That explosion was in the range of 30 times bigger than the Hiroshima nuclear bomb.”

The meteorite in Siberia was about 10 tons, less than the size of the boulder the Asteroid Redirect Mission will collect.

A larger asteroid in the early 1900s exploded with even greater force, Holdren said during a news conference.

“If we’re going to be as capable of a civilization as our technology allows, we need to be prepared for even those rare events, because they could do a lot of damage to the Earth,” Holdren said. “As part of that preparation, we have the planetary defense aspect of the asteroid retrieval mission.”

Muirhead expects commercial entities will watch the redirect mission closely.

Asteroids likely contain valuable resources that could someday be mined to resupply exploration missions or for commercial purposes.

Four aerospace companies are competing to build the spacecraft for the Asteroid Redirect Mission. Like the Space Launch System and the Orion crew capsule under development, Muirhead sees the mission as the prototype for future space hauling and mining endeavors.

“We think this is the first generation of this kind of spacecraft that will be used by NASA and commercial ventures,” Muirhead said.