The spacecraft traveled over 200 million miles and four years to briefly bump into Bennu, blow it up with compressed gas and collect bits of the surface. On October 21, the space agency shared the first series of images from the daring operation, revealing a delicate but explosive moment between stone and robot.
When the spacecraft’s robot take-out arm, called the Touch-And-Go Sample Acquisition Mechanism, or Tagsam, touched Bennu, it performed the equivalent of a cosmic pickpocketing maneuver. Mission planners expected the total contact time between the arm and the asteroid to be less than 16 seconds. When the preliminary data were released, it showed that the contact period was only six seconds, with much of the sample collection taking place only in the first three.
The spacecraft, which operates largely autonomously due to the 18-minute communication delay with mission control on Earth, fired a gas canister through Tagsam, which disturbed the surface of Bennu and forced a sample into the arm collector head.
Photos taken of the head on October 22 showed that so many specimens were collected that some larger rocks seemed to fail to get all the way inside, with a mylar flap being tickled to seal the container partially open, allowing some small pieces dust and pebbles to escape back into space.
Sample storage was originally scheduled for Nov. 2, but NASA instead moved the multi-day procedure up to Tuesday.
“The abundance of material we collected from Bennu made it possible to expedite our decision to store,” Dante Lauretta, OSIRIS-REx lead researcher at the University of Arizona, said in a statement.
Osiris-Rex marks a boulder
As the spacecraft approached and then spent two years in orbit and surveying Bennu, it became clear that this small world is different from what scientists expected. The team was hoping to find a number of sand surfaces that were ideal for sampling, but it turns out that Bennu is a pile of bricks with a rugged terrain scattered with rocks.
About 24 hours after the operation, NASA shared the first images of the touchdown operation captured by the spacecraft. Tagsam moves into position and its sampling head comes in contact with the surface of Bennus before the explosive nitrogen burn-out is fired. The operation kicks up a ton of dirt flying around the procurement arm. It really is something!
Although the above GIF appears relatively quickly, the operation continued much more delicately. The arm was lowered at about 10 centimeters per second, much slower than walking pace when it contacted the test site.
The team’s goal is to collect about 60 grams of dust, dirt and pebbles from the surface of Bennu. It reported on October 23 that it believes Osiris-Rex collected a sufficient sample and moved to start stewing it quickly, skipping a scheduled sample mass measurement and canceling a brake burn to keep the acceleration of the spacecraft to a minimum.
“We are working to keep up with our own success here and my job is to return as big a sample of Bennu as possible,” Lauretta said.
While the procedure for collecting the sample was performed autonomously by the spacecraft, storing the sample is a much slower step-by-step process of mission control that sends commands and evaluates the results before proceeding to the next step.
The mission joins Japan’s Hayabusa andin annals of asteroid exploration. Hayabusa sampled and returned a small amount of material from the asteroid Itokawa, and Hayabusa2 is in the process of returning a significant sample of the space rock Ryugu.
With the test now placed on 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.