January 1, 2019
NASA's OSIRIS-REx Probe Slips Into Orbit Around Asteroid Bennu, Breaks Double Record

The last day of 2018 has been very eventful for NASA. The agency has hit incredible milestones with two of its ongoing space missions, New Horizons and OSIRIS-REx.

As New Horizons was preparing for its epic flyby of Ultima Thule at the edge of the solar system, OSIRIS-REx was making history a lot closer to home. Launched on September 8, 2016 -- as NASA's first asteroid sampling mission -- OSIRIS-REx finally entered a close orbit around asteroid Bennu on December 31, the space agency announced yesterday.

According to NASA, the OSIRIS-REx spacecraft slipped into a tight orbit around asteroid Bennu at 2:43 p.m. EST, breaking two records in the process.

On the one hand, the probe has just set a new record for the closest orbit of a celestial body. The spacecraft is currently circling Bennu at a distance of about a mile (1.75 kilometers) from the asteroid's center.

On the other hand, the 1,650-foot-wide space rock has now become the smallest planetary object to ever be orbited by a man-made spacecraft.

"Inching around the asteroid at a snail's pace, OSIRIS-REx's first orbit marks a leap for humankind. Never before has a spacecraft from Earth circled so close to such a small space object — one with barely enough gravity to keep a vehicle in a stable orbit."
To settle into its record-breaking orbit around asteroid Bennu, OSIRIS-REx performed a single eight-second burn of its thrusters, coming in closer to the space rock than any other probe has ever ventured to a celestial body. The previous holder of the record for closest orbit was the European Space Agency's Rosetta spacecraft, which famously studied the comet 67P/Churyumov-Gerasimenko after sliding into an orbit four miles from its center in May of 2016.

Commenting on the mission's momentous achievement, OSIRIS-REx principal investigator Dante Lauretta -- a researcher at the University of Arizona, Tucson -- said that everything went swimmingly for the pioneering spacecraft.

"The team continued our long string of successes by executing the orbit-insertion maneuver perfectly. With the navigation campaign coming to an end, we are looking forward to the scientific mapping and sample site selection phase of the mission."
This latest milestone comes after two weeks of close flybys of the asteroid's poles and equator, from a distance of 4.3 miles away. Completed on December 16, this preliminary survey phase yielded crucial data on the mysterious asteroid, one that scientists knew very little about hitherto.

Mosaic image of asteroid Bennu composed of 12 PolyCam photos taken on December 2, 2018, by the OSIRIS-REx spacecraft from a range of 15 miles.
NASA/Goddard/University of Arizona
Mosaic image of asteroid Bennu composed of 12 PolyCam photos, taken by OSIRIS-REx on December 2, 2018, from a distance of 15 miles away.

"Our orbit design is highly dependent on Bennu's physical properties, such as its mass and gravity field, which we didn't know before we arrived," said OSIRIS-REx's flight dynamics system manager Mike Moreau -- who is based at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"Up until now, we had to account for a wide variety of possible scenarios in our computer simulations to make sure we could safely navigate the spacecraft so close to Bennu. As the team learned more about the asteroid, we incorporated new information to hone in on the final orbit design."
A Busy Month For The OSIRIS-REx Mission

As the Inquisitr previously reported, OSIRIS-REx first reached asteroid Bennu on December 3, parking within 12 miles of its surface. Nestled more than 70 million miles from our planet -- between the orbits of Earth and Mars -- the diamond-shaped space rock is strewn with boulders. This poses a number of challenges for the mission's sample collection phase, which is due to begin next year.

To scope out the asteroid's rugged terrain, OSIRIS-REx snapped a close-up view of Bennu on the eve of their big rendezvous, and produced the most insightful 3D model of the asteroid's shape created thus far. After taking a good look at the space rock with two of its five scientific instruments, OSIRIS-REx also uncovered traces of water on Bennu's surface, as reported by the Inquisitr in December.

What's Next For OSIRIS-REx

OSIRIS-REx will remain in orbit around asteroid Bennu until mid-February. Although the spacecraft is currently in the most stable possible orbit around Bennu, the mission's team will need to occasionally refine the probe's position to make sure that it stays safe.

"The gravity of Bennu is so small, forces like solar radiation and thermal pressure from Bennu's surface become much more relevant and can push the spacecraft around in its orbit much more than if it were orbiting around Earth or Mars, where gravity is by far the most dominant force," explained Dan Wibben, OSIRIS-REx maneuver and trajectory design lead at KinetX Aerospace in Simi Valley, California.

To ensure the safety of the spacecraft, the team will employ "trim" maneuvers to correct its orbit if and when necessary. Once this phase of the mission is over, OSIRIS-REx will fly away from Bennu, and will begin another survey phase of the asteroid -- engaging in a second series of close flybys.

Short for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, the OSIRIS-REx spacecraft is scheduled to swoop down on Bennu in July of 2020. At that time, it will grab at least 2.1 ounces of regolith -- surface material made up of dirt and rock fragments -- before heading back to Earth in March of 2021.