NASA’s OSIRIS-REx Completes Last Asteroid Flyby Before Heading Home

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NASA’s ambitious Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) has been in orbit of the asteroid Bennu since 2018, but it’s getting ready to call it a day and head home. NASA reports that OSIRIS-REx has completed a last-minute addition to its mission profile: one final flyby of Bennu to see how its activities changed the surface of the object. 

OSIRIS-REx arrived at Bennu in late 2018, but NASA spent almost two years studying the space rock before OSIRIS-REx got down to business. The spacecraft’s Touch-and-Go Sample Acquisition Mechanism (TAGSAM) allowed it to drift down and tap the asteroid, discharging a burst of compressed nitrogen. OSIRIS-REx did just that in late 2020, scooping up what could be more than two pounds of regolith. NASA would have considered the mission a success at just 2.1 ounces (60 grams). 

NASA says OSIRIS-REx will depart Bennu on May 10th. The long wait is mostly thanks to orbital mechanics — if the spacecraft waits until May to leave orbit, it will use less fuel to get back to Earth. This also gave the team time to plan the now-complete final tour, which happened early on April 7th. 

OSIRIS-REx spent almost six hours taking images of Bennu during the pre-programmed maneuver. It covered more than a full rotation of the asteroid, but the area around the “Nightingale” sample site will be the most interesting. “By surveying the distribution of the excavated material around the TAG site, we will learn more about the nature of the surface and subsurface materials along with the mechanical properties of the asteroid,” said Dr. Dante Lauretta, principal investigator for OSIRIS-REx at the University of Arizona. 

With the flyby done, all NASA has to do now is download the data. That’s easier said than done, though. At a distance of 185 million miles (297 million kilometers), the Deep Space Network can only manage a data rate of 412 kilobits per second. Plus, OSIRIS-REx has to share time on the network with NASA’s other space missions. With just a few hours of downloading per day, NASA expects it will take another week to get the multiple gigabytes of data OSIRIS-REx collected. 

After getting underway on May 10th, it will take OSIRIS-REx two years to return home. The sample container with pristine samples of an ancient asteroid should land in the Utah Test and Training Range on September 24, 2023.

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