NASA protects sample of asteroid Bennu to send home on Earth



The spacecraft’s sampling arm, called the Touch-And-Go Sample Acquisition Mechanism, over the target sampling site during a general rehearsal in April.


From NASA asteroid hunter Osiris-Rex completed an important part of its mission last week, managing to pick up rocks from the surface of the potentially dangerous space rock Bennu. The sample was so abundant that it began to leak into space, which led to a recall maneuver that the mission team reported on Thursday was successful.

The spacecraft traveled more than 200 million miles and four years to briefly hit Bennu, blow it up with compressed gas and collect bits of its surface. On October 21, the space agency shared the first batch of images of the daring operation, revealing a delicate but explosive moment between the rock and the robot.

When the spacecraft’s robotic sampling arm, called the Touch-And-Go Sample Acquisition Mechanism, or Tagsam, landed in Bennu, it performed what amounts to a cosmic pickpocket maneuver. Mission planners expected the total contact time between the arm and the asteroid to be less than 16 seconds. When preliminary data were released, they showed that the contact period was only six seconds, with much of the sample collection taking place in the first three.

The spacecraft, which operates largely autonomously due to the 18-minute delay in communications with Earth mission control, fired a can of gas through the Tagsam that broke through Bennu’s surface and forced a sample into the head of the arm’s collector.

Photos taken from the head on October 22 showed that so much sample was collected that some larger rocks seemed unable to reach the interior, attaching a mylar flap designed to seal the partially opened container, allowing some small pieces of dust and pebbles to escape back to space.

Captured by the spacecraft’s SamCam camera on October 22, this series of three images shows the head of the Osiris-Rex sampler filled with rocks and dust collected from the surface of Bennu. They also show that some of these particles are slowly escaping from the sampler head.


Sample storage was originally scheduled for November 2, but NASA changed the procedure from several days to Tuesday.

“The abundance of material we collected from Bennu made it possible to streamline our decision to stock,” said Dante Lauretta, principal researcher at OSIRIS-REx at the University of Arizona, in a statement.

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Osiris-Rex marks a stone

As the spacecraft approached and then spent two years orbiting and inspecting Bennu, it became clear that this small world is different than what scientists had expected. The team hoped to find a series of sandy surfaces ideal for sampling, but Bennu was found to be a pile of rubble, with rugged terrain covered with stones.

About 24 hours after the operation, NASA shared the first images of the landing operation captured by the spacecraft. The Tagsam moves into position and its sampling head makes contact with Bennu’s surface before the explosive explosion of nitrogen is fired. The operation raises a ton of debris flying around the acquisition arm. It’s really amazing!



Although the GIF above looks relatively fast, the operation proceeded much more delicately. The arm was lowered at about 10 centimeters per second, much slower than the pace of walking, when it came into contact with the sample site.

The team’s goal is to collect about 60 grams of dust, dirt and pebbles from Bennu’s surface. He reported on October 23 that he believes Osiris-Rex collected enough sample and moved to start storing it quickly, skipping a planned sample mass measurement and canceling a braking burn to keep the spacecraft’s acceleration to a minimum.

“We are working to maintain our own success here, and my job is to safely return the largest possible sample of Bennu,” said Lauretta.

The Osiris-Rex team celebrates at the touchdown.


Although the procedure for collecting the sample was done autonomously by the spacecraft, storing the sample is a much slower, step-by-step process, with mission control sending commands and evaluating the results before proceeding to the next step.

The mission joins the Japanese Hayabusa and Hayabusa-2 Missions in the annals of asteroid exploration. Hayabusa took a sample and returned a small piece of material from the asteroid Itokawa, and Hayabusa2 is in the process of returning a significant sample of Ryugu.

With the sample now stored in Osiris-Rex, the team will begin preparations for a long journey back to Earth, with a planned landing in the Utah desert in September 2023.


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