NASA’s OSIRIS-REx spacecraft is heading home. After a successful visit to the asteroid Bennu that lasted more than two years, the mission broke orbit today and set course for Earth. Most robotic missions are a one-way affair, but OSIRIS-REx wasn’t going to an asteroid just to look around. It grabbed a souvenir in the form of about 2 pounds of regolith, and scientists on Earth can’t wait to get their hands on it.
OSIRIS-REx (the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) launched in 2016 and rendezvoused with Bennu in late 2018. This 500-meter carbonaceous asteroid is considered a potential Earth impactor based on its orbit, but there is no immediate risk of it crossing paths with our planet. However, its relative proximity made it an ideal target for exploration.
After reaching Bennu, OSIRIS-REx conducted a detailed survey of the surface, identifying several possible landing sites. NASA eventually chose one nicknamed Nightingale, and OSIRIS-REx touched down late last year. The flexible sampling arm is the only part that came in contact with the surface, but a burst of compressed nitrogen launched a plume of dust and pebbles into the container.
NASA had planned for additional sampling runs if necessary, but the robot was literally overflowing with space rocks. Rather than depart Bennu right away, OSIRIS-REx hung around and took additional photos. It wrapped up the last flyby in April, but waiting until May 10th was always the plan. By leaving Bennu on that day, NASA minimized the amount of fuel the spacecraft would use to get home.
The current goal is to get OSIRIS-REx within 6,000 miles of Earth in September 2023, allowing it to drop off the sample container. That module will hopefully land safe and sound in the Utah Test and Training Range. The team will execute course corrections several months before the spacecraft reaches Earth to ensure the sample pod drops into the atmosphere at the proper angle. If for some reason OSIRIS-REx misses the target, NASA has a backup plan to try again in 2025.
If the return phase goes well, the team might have enough fuel left to send the spacecraft on a mission to a second asteroid. While it would not be able to return a second sample to Earth, it has instruments to conduct useful science experiments in situ. NASA will decide if such a mission extension is feasible later this summer.
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