NASA is going on a $1.25-billion road trip, and all we’re getting is this lousy boulder.

Today, the space agency announced a modified plan for its Asteroid Redirect Mission: Instead of bringing an entire asteroid back to lunar orbit, an uncrewed spacecraft will snag a boulder.

“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,” says NASA Associate Administrator Robert Lightfoot. “Let’s get on with it.”

As described during a news conference, NASA will select a final destination for its spacecraft in 2019. There’s already a space-rock short list that includes Itokawa, Bennu, and 2008 EV5, the last of which is currently at the top of the list. The spacecraft will launch in December 2020, then spend about two years heading to an asteroid in Earth's neighborhood.

Once it gets there, it will retrieve a boulder up to 13 feet wide from the surface, then spend anywhere between 215 and 400 days circling the asteroid, using its gravity to nudge the giant rock into a different orbit.

Next, the spacecraft will return its prize, the boulder, to a stable orbit around the moon in 2025. At that point, astronauts could rendezvous with the boulder and collect samples.

Why It Matters

If successful, the mission will be the first to purposefully place a hefty chunk of space rock anywhere near Earth. Astronauts will dock with the retrieved boulder and collect data that will help scientists learn more about the particular type of asteroid it came from.

The Big Picture

NASA says the mission is a stepping-stone toward human exploration of Mars, as well as a chance to test planetary defense strategies. While the spacecraft is visiting its target asteroid, it will be gently redirecting it to a different orbit, allowing scientists to test a possible way to deflect large asteroids heading for Earth.

Several of the mission’s components, such as solar electric propulsion, are being considered for extended missions into deep space.

What's Next

NASA is moving into what’s called Phase A, where mission plans are being refined. Target selection won’t happen for a few more years, and NASA needs to get its heavy lifter—the Space Launch System and Orion crew capsule—up and running to actually send humans to lunar orbit.

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