O-REx Collects Surfeit of Samples from Bennu

O-REx Collects Surfeit of Samples from Bennu

In a hastily called press conference this afternoon, NASA announced that the OSIRIS-REx spacecraft collected so much material when it touched down on Bennu that it overfilled the collection device. Some of the larger pieces of material are preventing a flap from closing to secure the material inside.  Time now is of the essence to get the samples safely stowed in the canister that will return them to Earth.

“Science never sleeps,” began Thomas Zurbuchen, head of NASA’s Science Mission Directorate.  Since the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx or O-REx) spacecraft touched down on Bennu at 6:12 pm EDT (Earth-receive time) on Tuesday, the NASA-University of Arizona-Lockheed Martin team has been eagerly looking to see what was captured during the brief 6-second contact with the surface.

It turns out O-REx grabbed much more rock and soil than anyone hoped. The surface was softer than expected and the sample head may have penetrated 24-48 centimeters into the soil. The samples filled the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) head so much that a mylar flap meant to contain them is stuck open and some of the material is drifting into space.

The goal was to collect at least 60 grams (2 ounces), and as much as 2 kilograms (4.4 pounds), of material for return to Earth.  To determine how much was obtained, the plan was to first look at the sample head using an onboard camera and then to spin the spacecraft to determine how its moment of inertia had changed, from which the mass of the added material could be calculated.

After getting images back yesterday, however, they decided to call off the spin maneuver as well as a braking maneuver that would have put the spacecraft back into orbit around Bennu.

They do not want to make any unnecessary spacecraft movements lest they lose any more.

That means they will not know exactly how much material was collected until the sample returns to Earth in 2023, but Principal Investigator Dante Lauretta feels pretty confident they got close to the 2 kilogram upper limit.

What matters now is getting the material safely stowed inside the Sample Return Capsule, the only part of the spacecraft that will land on Earth. The O-REx team is working on the precise steps needed since the process is playing out differently than expected. They also need to coordinate with the operators of NASA’s Deep Space Network (DSN) that transmits data back and forth to O-REx since it also handles many other spacecraft.  Zurbuchen said he has asked them to make O-REx a priority.

At the moment, they plan to begin the stowing process on Tuesday.

O-REx was designed to make at least two more attempts to obtain a sample if the first try failed. After touching the surface, the spacecraft fired a back-away burn of 40 centimeters/second (cm/s) and the plan was to fire the rockets again to brake the movement and put the spacecraft back into orbit around Bennu, ready for a second touchdown if needed. Now that the decision is to skip that braking maneuver, O-REx will continue to move away from Bennu at 40 cm/s and not resume orbit.

“We have said goodbye to Bennu,” Lauretta explained, although the main engines needed to send O-REx back to Earth still will not be fired until March when Earth and Bennu are correctly aligned.  It will take over two years for it to make the 207 million mile (334 million kilometer) trip, landing in Utah on September 24, 2023.

The situation is creating something of a scramble as the O-REx team replans next steps, but as Zurbuchen says, it is not a bad problem to have.

“And although we may have to move more quickly to stow the sample, it’s not a bad problem to have. We are so excited to see what appears to be an abundant sample that will inspire science for decades beyond this historic moment.” — Thomas Zurbuchen


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