May 10, 2021
After almost five years in space, NASA’s Origins, Spectral Interpretation, Resource Identification, Security and Regolith Explorer (OSIRIS-REx) spaceship is on its way back to Earth with an abundance of stones and dust from the near-Earth asteroid Bennu.
On Monday, May 10, at 4:23 p.m. EDT, the spaceship fired its main engines at full throttle for seven minutes – the most significant maneuver since arriving in Bennu in 2018. This burn propelled the spaceship at a speed of 600 miles per hour away from the asteroid (almost 1,000 kilometers per hour), which means a 2.5-year cruise towards Earth.
After the release of the sample capsule, OSIRIS-REx has completed its main task. It will fire its engines to fly safely past Earth and place it on a trajectory to orbit the Sun within Venus’ orbit.
After two orbits of the sun, the OSIRIS-REx spacecraft is scheduled to reach Earth on September 24, 2023. When it returns, the capsule with Bennu pieces will separate from the rest of the spacecraft and enter the earth’s atmosphere. The capsule will parachute to the Utah Test and Training Range in the Utah western desert, where scientists are waiting to find it.
“The many successes of OSIRIS-REx have shown how daring and innovative real-time exploration is,” said Thomas Zurbuchen, Associate Administrator for Science at NASA headquarters. “The team rose to the challenge and now we have a pristine piece of our solar system on its way back to Earth, where many generations of researchers can reveal its secrets.”
To accomplish the mission’s multiannual plan, a dozen navigational engineers performed calculations and wrote computer code to instruct the spaceship when and how to move away from Bennu. After Bennu’s departure, the team’s next critical goal is to get the sample safely back to earth. This includes planning future maneuvers to keep the spaceship on course throughout its journey.
“Our whole mindset was,” Where are we in space in relation to Bennu? “Said Mike Moreau, OSIRIS-REx deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.” Now our mindset has shifted to ‘Where is the spaceship in relation to Earth?’
The navigational cameras, which helped orient the spacecraft with respect to Bennu, were turned off on April 9 after taking their final images of the asteroid. With Bennu in the rearview mirror, engineers use NASA’s Deep Space Network for global communication systems for space vehicles to control the OSIRIS-REx by sending radio signals. By measuring the frequency of the waves returned by the spacecraft’s transponder, engineers can determine how fast the OSIRIS-REx is moving. Engineers measure how long it takes for radio signals from the spaceship to return to Earth in order to determine its location.
Exceed mission expectations
The May 10 departure date was determined precisely based on Bennu’s alignment with the earth. The goal of the repatriation maneuver is to bring the spaceship around the earth within approximately 10,000 kilometers in September 2023. Although OSIRIS-REx still has enough fuel, the team is trying to conserve as much as possible for a potential extended mission to another asteroid after the sample capsule is returned to Earth. The team will investigate the feasibility of such a mission this summer.
The spacecraft’s heading is primarily determined by the sun’s gravity, but engineers occasionally need to make small course adjustments by burning the engine.
“We need to make regular corrections to bring the sample release trajectory closer and closer to the Earth’s atmosphere and to account for any small errors that may have accumulated since the last fire,” said Peter Antreasian, OSIRIS-REx director of navigation at KinetX Aerospace. The company is based in Simi Valley, California.
The team will make course adjustments a few weeks before re-entry to pinpoint the location and angle for the release of the sample capsule into the Earth’s atmosphere. If you go too deep, the capsule can pop out of the atmosphere like a pebble jumping off a lake. too high and the capsule could burn due to friction and heat from the atmosphere. If OSIRIS-REx doesn’t release the capsule, the team will have a backup plan to steer it away from Earth and try again in 2025.
“There is a lot of emotion in the team about the departure,” said Moreau. “I think everyone has a great sense of achievement because we faced all these daunting tasks and were able to achieve all of the goals we were set. But there is also nostalgia and disappointment that this part of the mission is coming to an end. “
OSIRIS-REx exceeded many expectations. Most recently, in the midst of a global pandemic, the team performed the mission’s most critical operation flawlessly, collecting more than 60 grams of soil from Bennu’s surface.
Before the sample was taken, a few surprises kept the team busy. For example, a week after the spacecraft entered its first orbit around Bennu on December 31, 2018, the team discovered that the asteroid was ejecting small pieces of rock into space.
“We had to mix up to make sure the small particles that were being ejected from the surface didn’t pose a threat to the spaceship,” said Moreau.
Upon arrival at the asteroid, the team members were also amazed that Bennu was littered with boulders.
“We really got the idea that we would arrive on an open property asteroid,” said Heather Enos, assistant senior investigator for OSIRIS-REx at the University of Arizona, Tucson. “The reality was a big shock.”
To overcome the extreme and unexpected ruggedness of Bennu’s surface, engineers had to quickly develop a more accurate navigation technique to target fewer than expected locations for sampling.
The OSIRIS-REx mission was instrumental in confirming and refuting several scientific findings. Among those confirmed was a technique that used observations from Earth to predict that the minerals on the asteroid would be carbon-rich and show signs of ancient water. One finding that proved unsuccessful was that Bennu would have a smooth surface, which scientists predicted by measuring how much heat was being radiated from its surface.
Scientists will use the information Bennu has gathered to refine theoretical models and improve future predictions.
“This mission underscores why we need to do science and exploration in a variety of ways – both from Earth and near space – because assumptions and models are just that,” Enos said.
Goddard offers the entire mission management, the system technology as well as the security and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the lead investigator. The university leads the science team and the scientific observation planning and data processing of the mission. Lockheed Martin Space in Littleton, Colorado built the spacecraft and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, administered by NASA’s Marshall Space Flight Center in Huntsville, Alabama for the Agency’s Directorate of Scientific Missions in Washington.
Further information on OSIRIS-REx can be found at: