OSIRIS-REx is NASA’s first asteroid-sampling mission and it will scoop up its pristine prize in just a few months. Last week, the spacecraft successfully performed its second and final rehearsal approaching the surface of asteroid Bennu before going back to its operational orbit.

In this latest maneuvering, OSIRIS-REx performed three of the four stages it will employ on October 20, when it will move down from its current orbit, adjust itself, touch the ground, and go back into space. The spacecraft moved from about 1 kilometer (0.6 miles) from the surface to just 125 meters (410 feet) above it, where it performed a "Checkpoint" burn, where OSIRIS-REx automatically checked its speed and trajectory. 

After that, the spacecraft descended for another 8 minutes, reaching the point where it could do a Matchpoint burn, where OSIRIS-REx matches with Bennu’s rotation, flying in perfect synchronicity with the surface of the asteroid. After this, the spacecraft dropped for another 3 minutes, arriving just 40 meters (131 feet) above its target, the Nightingale sample site, located within a crater in the northern hemisphere of Bennu. This is the closest OSIRIS-Rex has ever been to the surface of Bennu.

Reaching that point, the spacecraft performed its back-away burn and went back to its safe home orbit. While the actual sample collecting was not rehearsed, the probe successfully deployed its Touch-And-Go Sample Acquisition Mechanism (TAGSAM), the sampling arm that will collect the soil.

“Many important systems were exercised during this rehearsal – from communications, spacecraft thrusters, and most importantly, the onboard Natural Feature Tracking guidance system and hazard map,” OSIRIS-REx principal investigator Dante Lauretta of the University of Arizona said in a statement. “Now that we’ve completed this milestone, we are confident in finalizing the procedures for the TAG event. This rehearsal confirmed that the team and all of the spacecraft’s systems are ready to collect a sample in October.”

Performing this rehearsal is extremely important. Bennu is currently 288 million kilometers (179 million miles) from Earth. A signal to the spacecraft takes 16 minutes to arrive. So OSIRIS-REx will have to be able to do the whole maneuver, and avoid any dangers on the surface, all by itself.

After the collection, OSIRIS-REx will remain orbiting around Bennu for several more months, before coming back home in 2023 to deliver its precious cargo. By then it will be the third spacecraft to bring an asteroid sample back to Earth after Japan's Hayabusa and Hayabusa2 missions successfully collected samples from Ryugu.