Tracking the Bennu Sample Capsule's Separation from OSIRIS-REx

UArizona Space4 Center lab manager Neil Pearson, aerospace and mechanical engineering graduate student Tanner Campbell and Vishnu Reddy, professor at the UArizona Lunar and Planetary Laboratory and director of the Space4 Center, observe the separation of the OSIRIS-REx sample return capsule from the spacecraft from Kihei, Hawaii, on Sept. 24.

By Niranjana Rajalakshmi, University Communications - October 25, 2023

Hours before the OSIRIS-REx sample return capsule blasted into Earth’s atmosphere and landed safely in the Utah desert on Sept. 24, a small University of Arizona team was tracking another key part of the mission: the capsule's separation from the spacecraft.

With three optical telescopes at different locations, the team of faculty, students and staff from the Lunar and Planetary Laboratory and the Space4 Center joined industry partners in front of computer screens, watching as one dot – the spacecraft – became two when it released the capsule at around 3:42 a.m. Tucson time.

two dots separating from one another against a dark gray background

A team from the UArizona Lunar and Planetary Laboratory and the Space4 Center used telescopes to capture the moment, at around 3:42 a.m. Tucson time, when the OSIRIS-REx spacecraft released the capsule with the sample of the asteroid Bennu, sending it toward Earth. Two dots in the center-right of the frame show the capsule and the spacecraft as they separate.Vishnu Reddy/University of Arizona

While tracking the capsule with optical telescopes wasn't officially part of NASA's historic UArizona-led OSIRIS-REx asteroid sample return mission, the event can be used as an analog for tracking an asteroid on a collision course with Earth if one were ever discovered, said Vishnu Reddy, who led the project.

"The techniques used to track an incoming asteroid on its terminal trajectory before it enters the Earth’s atmosphere are the same as us tracking the sample return capsule before it reaches the atmosphere," said Reddy, a planetary sciences professor in the Lunar and Planetary Laboratory and the director of the Space4 Center.

The capsule separation from the spacecraft was visible only between central Australia and the eastern Pacific Ocean. Within that sliver, the team observed the return using three telescopes: two at Siding Spring Observatory in Australia that were operated remotely at the UArizona campus, and one in Kihei, Maui, Hawaii, where researchers observed in person. 

After the separation, two telescopes tracked the capsule while one remained on the spacecraft. About 20 minutes after the separation, the spacecraft fired its engines and began its multiyear journey to another asteroid, Apophis. By collecting data on the spacecraft, the team also hopes to better understand how spacecraft maneuver through orbits between the Earth-moon system – information useful for space situational awareness, which is the practice of tracking celestial bodies, understanding their environment and predicting their future positions.

Along with Reddy, the team included graduate students David Cantillo and Adam Battle from the Lunar and Planetary Laboratory and Tanner Campbell from the Department of Aerospace and Mechanical EngineeringScott Tucker from Starizona, a Tucson-based small business, and Neil Pearson, the lab manager of Reddy's research group, were also part of the group. The team collaborated on the project with scientists supported by the NASA Planetary Defense Coordination Office and the Air Force Research Lab for work relevant to their respective missions.

Tracking at Maui started at 2 a.m. Tucson time, with the spacecraft appearing on the team's computer screens as a blurry dot about 90,000 miles away from the observing location. Successive images of the dot showed it hurtling through space, while the stars in the image remained static.

"We were one of the few research teams that optically tracked the sample return capsule using telescopes just before it entered the atmosphere," Reddy said. "We picked out the object right away and tracked it all the way to the capsule separation, when one object became two."

While the capsule separated from the spacecraft at 3:42 a.m. Tucson time, the UArizona team estimated it would take an additional 20 minutes to see both objects as two individual dots, given the resolution of their telescopes. They were surprised to observe the separation on their computer screens after only eight minutes, at 3:50 a.m. As they collected images, the group processed the data in real time to verify its path.

Lunar and Planetary Laboratory graduate students Adam Battle (left) and David Cantillo (right) track the OSIRIS-REx spacecraft and sample return capsule remotely using telescopes in Siding Spring, Australia.

Lunar and Planetary Laboratory graduate students Adam Battle (left) and David Cantillo (right) track the OSIRIS-REx spacecraft and sample return capsule remotely using telescopes in Siding Spring, Australia.Space4 Center

"There was a certain feeling of relief, knowing that the sample return capsule had successfully separated from that main spacecraft, and it was on its final journey home," Cantillo said. Cantillo and Battle observed remotely using the telescopes in Australia.

The Maui team continued to track the capsule until 7:38 a.m. Tucson time, a few minutes before it entered the Earth's atmosphere off the coast of California. The capsule traveled at more than 27,000 mph as it descended through Earth's atmosphere.

"This was one of the fastest objects we have ever tracked," Reddy said.

Prior to the Sept. 24 return, Cantillo and Battle developed and tested computer scripts that remotely controlled the telescopes in Australia. To enable tracking, the scripts included precise predicted positions of the spacecraft and capsule the team wanted to track at different times during their five-hour observation block and matched the exact rate at which the spacecraft would be traveling.

What made these observations unique was that the work was mostly front-loaded in terms of planning, and setting up the scripts that were run on telescopes, Cantillo said.

"Fortunately, everything worked flawlessly, and we got all the data we planned for," Battle said.

Tracking the Bennu sample capsule's separation from OSIRIS-REx