OSIRIS-REx capsule closed following successful Bennu sample collection
NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft collected enough soil samples of the asteroid Bennu on its first attempt that mission controllers commanded the spacecraft to close its Sample Return Capsule (SRC).
On Tuesday, October 20, OSIRIS-REx used its 11-foot robotic arm to collect samples of Bennu from a site named Nightingale, near the asteroid’s north pole, in an operation titled “Touch and Go.” In the days following the collection, the spacecraft sent back images of the samples collected so mission scientists could determine whether a second collection was needed.
During the maneuver, the robotic arm delved up to 19 inches (48 centimeters) below Bennu’s surface.
Mission scientists sought to collect a minimum sample of two ounces though ideally they hoped for twice as much.
Images returned by the spacecraft indicated OSIRIS-REx‘s Touch-and-Go Sample Acquisition Mechanism (TAGSAM) showed the instrument over-performed, collecting such a large amount of samples that some of the larger rocks grabbed initially prevented the sampling mechanism from properly closing. This resulted in some of the sample being released into space.
In spite of that loss, mission scientists are confident the probe still has more than enough sample material, meaning a second collection attempt is not needed.
To prevent further sample loss, the mission team decided to skip plans to weigh the sample, scheduled for Saturday, October 24, and to cancel an engine burn that would slow down the spacecraft’s move away from Bennu’s surface.
“The challenge that we have in front of us is due to the fact that the TAGSAM is probably really full of material.” meaning the top priority now “is to get this sample safely stowed and minimize any more loss,” said principal investigator Dante Lauretta of the University of Arizona in a news conference on Friday, October 23.
Beginning October 24, mission scientists and engineers spent two days stowing the sample, using NASA’s Deep Space Network (DSN) to relay commands to and from the spacecraft.
The process required them to review images and telemetry from each step to confirm success before moving on to the next step. Because OSIRIS-REx is currently over 205 million miles (330 million km) from Earth, communications each way are delayed by slightly over 18.5 minutes.
Throughout the four-day effort, the mission team also had to regularly review TAGSAM‘s wrist alignment to make sure the samples were being correctly placed in the SRC and that any escaping particles did not hamper the stowage procedure.
“Given the complexity of the process to place the sample collector head onto the capture ring, we expected that it would take a few attempts to get it in the perfect position. Fortunately, the head was captured on the first try, which allowed us to expeditiously execute the stow procedure,” explained OSIRIS-REx project manager Rich Burns of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
On Wednesday, October 28, the final step of the collection process was completed, as the lid of the SRC was closed and safely stored on the spacecraft.
Bennu is a rubble pile asteroid, meaning it is made up of a group of rocks held together by gravity. Estimated to be around 4.5 billion years old, it likely was part of a larger asteroid that broke apart from an impact in the solar system’s earliest years.
Because it has a one in 2,700 chance of impacting the Earth, Bennu is considered a near-Earth object. This is just one reason scientists are studying it. Asteroids and comets may have brought water and materials that make up the building blocks of life to Earth, so studying Bennu could give scientists insight into the origins of life in the solar system.
Data collected by OSIRIS-REx indicates Bennu’s surface contains carbon-rich material. Between five and ten percent of the asteroid’s mass is water.
“A piece of primordial rock that has witnessed our solar system’s entire history may now be ready to come home for generations of scientific discovery, and we can’t wait to see what comes, next,” said associate administrator of NASA’s Science Mission Directorate Thomas Zurbuchen, on the day the sample was taken.
The probe, which launched in September 2016 and arrived at Bennu in December 2018, will likely depart for its return to Earth in March of next year, when the launch window begins, based on the orbits of Bennu and Earth. It is expected to arrive back on Earth with the samples on September 24, 2023.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.