How NASA snagged a sample from an asteroid 220 million miles away

X marks the spot.
X marks the spot.
Image: NASA
We may earn a commission from links on this page.

“One of the more fun ways of engineering is thinking about all the things that can go wrong,” Olivia Billett says.

Billett is a Lockheed Martin engineer who led a team that designed and operated the scientific mission of the spacecraft OSIRIS-REx. This week, the vehicle appeared to snatch a geological sample from an asteroid 220 million miles away that it will return to earth, a stunning technical achievement. And one reason it did was that Billett and her colleagues were ready for some deep space surprises.

Billett and Lockheed have experience with missions to Mars and other planets, but faced new challenges when exploring the asteroid Bennu. “When you are in orbit around a planet, gravity is such dominant force and everything else is noise,” Billett explains. “You know exactly where the spacecraft will be relative to the planet weeks into the future.”

Bennu, though roughly the size of the Empire State building, is much smaller than a planet and has a weaker gravitational pull. That means everything from solar radiation to internal motion in the spacecraft can throw it off course. For planetary missions, Billett’s team might have weeks to design and test a maneuver. For this effort, they have been downloading info from the spacecraft’s sensors, plotting maneuvers, testing them, and sending the instructions back into space—overnight.

The design of OSIRIS-REx’s sample collector is perhaps the most unique aspect of the spacecraft—an 11-foot-long arm that began life as a plastic cup and a compressed air canister in an engineer’s garage. Called the TAGSAM, for touch-and-go sample acquisition mechanism, it is briefly pressed into Bennu’s surface, which it blasts with nitrogen gas, driving dust and small rocks into prepared containers.

A series of images captured by OSIRIS-REx shows the TAGASAM impacting the surface of Bennu.
Image: NASA

The mission launched in 2016, and when it arrived at Bennu in 2018, scientists were in for a surprise: They had anticipated Bennu’s surface would be like a sandy beach. Instead, it was fairly rocky. That meant that the spacecraft couldn’t rely on laser rangefinders to guide it to the surface, since they couldn’t distinguish between a rock and a patch of sand. Instead, OSIRIS-REx would use onboard cameras and software that could analyze the surface to guide it in for landing. The next two years were spent surveying Bennu and practicing for this week’s culminating touch-and-go.

In the days ahead, we’ll find out if OSIRIS-REx has gathered enough rocks and dust to begin its return journey, or if it needs to make one or two more tries at snatching a sample. If it all went well, the spacecraft will parachute its cargo down to New Mexico in 2024. Scientists—who came up with the idea for this mission more than eight years ago—eagerly await these materials because they could help explain how our solar system grew and changed over time, potentially increasing our understanding about the origins of life on Earth.

This game of astronomical tag has another motive—Bennu’s orbit will pass quite close to earth in the century ahead, with a small chance of a disastrous impact with our planet. The detailed understanding NASA has gained of the asteroid will make it possible to more accurately predict the asteroid’s path—and potentially allow us to take defensive action if Bennu comes to tag earth back.

A version of this story originally appeared in Quartz’s Space Business newsletter.