This procedure will take nearly four weeks. On Dec. 31, the spacecraft can then begin orbiting from about a mile out along the line that separates day and night on the asteroid, called the terminator. This is done to evenly distribute the pressure from the light of the sun on the spacecraft, Nolan said.

The terminator isn’t a great place to understand the surface of Bennu and choose a sample site, so the craft will come out of orbit multiple times in the next 18 months to make swooping passes around other sides of Bennu from varying distances to collect data, snap photos and get a more detailed understanding of the asteroid.

Bennu was discovered in 1999 and is the smallest planetary body that any spacecraft has ever orbited. It is 1,650 feet wide, which is slightly larger than the Empire State Building. Bennu travels at an average speed of 63,000 mph around the sun and has the most well-understood orbit of any asteroid.

The approach phase of the mission began when Bennu first appeared to the spacecraft as a dot of light Aug. 17 from 1.4 million miles away. Since then, OSIRIS-REx has been snapping photos as it puts on the brakes to learn as much as it can before arrival.