NASA on Bennu asteroid touchdown: Everything we know about TAG

This afternoon, NASA held an online conference to talk about TAG, an upcoming event under the OSIRIS-REx mission. During this event, which is scheduled to take place in a couple of weeks, the OSIRIS-REx spacecraft will briefly touchdown on the asteroid Bennu in order to collect a small sample of gravel before taking off again into orbit. The space agency has spent months preparing for TAG, including selecting the collection site and rehearsing the touchdown maneuvers.

It seems that despite the pandemic, everything about the Touch-and-Go (TAG) event is on schedule and therefore NASA is preparing for the touchdown scheduled to happen next month. On October 20, OSIRIS-REx will maneuver touchdown at Nightingale, the primary sample collection site selected by NASA. If the spacecraft is unable to make the collection at this destination for whatever reason, the space agency has already picked out the second most promising backup site for a second attempt.

Touchdown on Bennu will prove a bit more tricky than originally anticipated. As NASA reported months ago, Bennu is rockier than expected; it is home to large boulders that put the spacecraft at risk, making it particularly important to pick the right touchdown location.

In this case, Nightingale is a 52ft region located in the asteroid’s northern hemisphere. NASA explains that this region has the greatest amount of fine-grain materials for OSIRIS-REx to collect, but that there are big boulders the size of buildings surrounding it.

OSIRIS-REx itself is quite large — NASA describes it as around the size of a big van — meaning that it will require careful placement to touchdown in just the right spot without clipping any of the boulders. The touchdown will require a total of three maneuvers to get to the asteroid’s surface, including the four-hour trip down from orbit to Bennu. The rest of the process, including the sample collection and takeoff, will last around 30 minutes.

Of those 30 minutes, NASA says that the actual collection event will involve the spacecraft touching down on Bennu for a grand total of 16 seconds. A pressurized nitrogen bottle will be used to essentially blast some of the surface gravel upwards, where it will get caught in a collection head on the large spacecraft. After that, OSIRIS-REx will kick on its thrusters again, boosting itself back out into orbit around the small asteroid.

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