This summer, the OSIRIS-REx spacecraft will attempt to touch down onto the surface of asteroid Bennu and collect a sample to be brought back to Earth for the first time. But it’s no easy task to maneuver a spacecraft so close to an asteroid, getting it close enough to grab a sample without impacting too hard and damaging the craft. Not to mention the role of microgravity created by the asteroid’s mass.
So this week, NASA will perform a test run of the touchdown, called the “Checkpoint” rehearsal. This will bring OSIRIS-REx the closest it has ever come to Bennu, coming as close as within 243 feet of the asteroid.
In order to touchdown on the asteroid, the craft needs to fire its thrusters in three separate bursts. First, it will perform an orbit departure burn, in which it moves out of its current orbit around the asteroid. Then, when it reaches 410 feet above the asteroid, it will perform what is called the Checkpoint maneuver in which its position and speed are adjusted. A third burn carries the craft down toward the asteroid, with a Matchpoint maneuver performed just 164 feet from the surface to match the asteroid’s rotation, before a hopefully gentle touchdown.
In the Checkpoint rehearsal this week, OSIRIS-REx will perform the departure burn and Checkpoint maneuvers, in order to check the craft’s systems including imaging, navigation, and ranging during this first part of the descent. The rehearsal will take approximately four hours and will also include the extending of the craft’s robotic arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM).
Selecting the exact landing site for OSIRIS-REx took some time, as the surface of the asteroid turned out to be rather different than the scientists expected. They had thought that they would find beach-like flat surfaces on which they could land, but asteroid Bennu turned out to be covered in boulders which make landing much more challenging. But thanks to the public’s help, NASA was able to select an appropriate landing site late last year.
Another test rehearsal is planned for June this year, which will cover the Matchpoint burn and bring the craft down to an altitude of 82 feet. The real sampling mission is scheduled for August 25.
