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NASA's OSIRIS-REx spacecraft prepares for final asteroid-sampling rehearsal

OSIRIS-REx is expected to collect a sample from asteroid Bennu on Oct. 20. This artist's concept shows the trajectory and configuration of the spacecraft during its matchpoint rehearsal.
OSIRIS-REx is expected to collect a sample from asteroid Bennu on Oct. 20. This artist's concept shows the trajectory and configuration of the spacecraft during its matchpoint rehearsal.
(Image: © NASA/Goddard/University of Arizona)

NASA's OSIRIS-Rex spacecraft is preparing for its final rehearsal before touching down on asteroid Bennu this fall to snag a piece of space rock. 

OSIRIS-REx, which has been orbiting Bennu since 2018, is NASA's first asteroid-sampling spacecraft. The probe is scheduled to practice its touchdown sequence for a second time on Tuesday, Aug. 11. 

During the practice session, the spacecraft will rehearse the touch-and-go sample-collection event, similar to the mission's April 14 checkpoint rehearsal, which practiced the first two maneuvers of the descent. But this time, the spacecraft will add a third maneuver, called the matchpoint burn, and fly closer to the sample site, known as Nightingale, than it has before. 

Related: NASA's asteroid-sampling mission in pictures

As part of the matchpoint burn, OSIRIS-REx will fly in tandem with Bennu's rotation for the first time. This rehearsal provides the team with another opportunity to practice navigating the spacecraft through the descent maneuvers, as well as to test the spacecraft's imaging, navigation and ranging systems, according to a statement from NASA

During the Aug. 11 rehearsal, the $800 million OSIRIS-REx (Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer) mission will perform several different activities. Traveling at an average speed of 0.2 mph (0.3 kph), the spacecraft will fire its thrusters three separate times during its decent to the asteroid's surface. The first will pull the spacecraft out of its 0.6-mile-high (1 kilometer) orbit around Bennu. 

Other milestones in the rehearsal include extending the spacecraft's robotic sampling arm, collecting images for its autonomous navigation system, and moving its solar panels into position away from the asteroid's surface.

When OSIRIS-REx reaches an altitude of 410 feet (125 meters), it will perform the checkpoint burn and descend quickly toward Bennu's surface for about eight minutes. When the spacecraft is 164 feet (50 m) above the asteroid, it will fire its thrusters a third time to execute the matchpoint burn, slowing its rate of descent and aligning with Bennu's rotation. 

OSIRIS-REx will reach an altitude of only 131 feet (40 m) above the sample site — its closest approach yet — before heading back to orbit with a back-away burn, according to the statement.

Assuming the rehearsal goes smoothly, OSIRIS-REx will remain in its orbit around Bennu until it travels all the way to the asteroid's surface during its first sample collection attempt on Oct. 20. The samples are expected to be returned to Earth on Sept. 24, 2023.

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