OSIRIS-REx Successfully Begins Record-Breaking Orbit Around Asteroid Bennu

Mosaic image of asteroid Bennu. NASA/Goddard/University of Arizona

NASA’s OSIRIS-REx has successfully completed a close orbit around asteroid Bennu, smashing the record for smallest object ever orbited by a spacecraft, as well as the record for closest orbit. Bennu is just 492 meters (1,614 feet) in diameter, and the spacecraft is just 1.75 kilometers (1.09 miles) from the center of the asteroid.

OSIRIS-REx has now begun the next phase of its mission. It will continue to map the surface of the asteroid in detail, study its composition, and help researchers identify the best place for the probe to come down and collect a sample of Bennu. Once that happens, OSIRIS-REx will then fly back to Earth where it will arrive back in 2023.

“Entering orbit around Bennu is an amazing accomplishment that our team has been planning for years. The team continued our long string of successes by executing the orbit-insertion maneuver perfectly,” Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, said in a statement.

“With the navigation campaign coming to an end, we are looking forward to the scientific mapping and sample site selection phase of the mission.”

Getting the probe into this close orbit is not an easy task. Bennu’s gravity is extremely weak, about 5-millionth of Earth’s own, so other forces like the solar radiation and thermal pressure from Bennu’s surface are no longer negligible. The OSIRIS-REx navigation team used simulations from the most recent data to work out the best possible orbit and they are ready to perform small maneuvers to keep the craft on a stable orbit. If something unexpected happens, OSIRIS-REx is simply programmed to fly away.

“It’s simple logic: always burn toward the Sun if something goes wrong,” explained Coralie Adam, OSIRIS-REx lead optical navigation engineer at KinetX. While it is crucial to be prepared, Adam explained that thankfully this scenario is very unlikely to actually happen.

The Orbital phase will allow researchers to improve mass and gravity estimation of Bennu. This will be done by tracking precisely how OSIRIS-REx's trajectory is influenced by the asteroid. The data will also play a part in the short touchdown for sample collecting that will happen in the summer of 2020.

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