After a series of high-stakes maneuvers performed more than 200 million miles from Earth, NASA’s OSIRIS-REx spacecraft has successfully stowed its precious samples of the asteroid Bennu. The move follows a surprise leak first announced on October 23, as some of the spacecraft’s pristine space rocks slipped out of a jammed sampling mechanism and floated away into the void. The safeguarding of the sample ensures that the material—rocks and dust from the solar system’s origins—will safely make its way to Earth.
The sample was secured after a tense few days following OSIRIS-REx’s October 20 touchdown on Bennu, which made the spacecraft only the third—and NASA’s first—to collect a sample from an asteroid. But OSIRIS-REx did almost too good of a job: It picked up pieces of the asteroid large enough to wedge the sample-collection device partially open.
As soon as the team noticed the debris leak on October 22, OSIRIS-REx personnel canceled several planned maneuvers and tests to minimize any disturbances to the sample-collection device, called TAGSAM (Touch-And-Go Sample Acquisition Mechanism). To protect the material in the device, which will be returned to Earth in 2023, OSIRIS-REx’s controllers quickly acted to tuck the sample into a sealed capsule—a maneuver that was completed on October 28.
The successful stowing process comes as a welcome relief, as OSIRIS-REx’s cache of primordial dirt and rocks could shed light on how the planets—and maybe even life on Earth—came to be. By studying the ingredients that were present in the newborn solar system, scientists hope to unravel the 4.5 billion-year process that produced Earth and everything on it.
Just hours into the effort to safeguard the sample, OSIRIS-REx principal investigator Dante Lauretta acknowledged that the accelerated maneuver came with its own risks, but he stressed that quickly locking down the sample was the most prudent course of action.
“Once it’s in the return capsule, it’s all contained, and anything inside there is coming back to the surface of Earth,” he said on October 27.
On October 22, two days after touching Bennu, engineers realized that OSIRIS-REx's Touch-and-Go Sample Acquisition Mechanism (TAGSAM) sampling head on was leaking precious rocks and dust. The culprit: a mylar flap designed to keep the material in the head, wedged open by larger rocks.
Photograph by NASA/Goddard/University of ArizonaThe jammed sampling mechanism was the latest surprise thrown at OSIRIS-REx by Bennu, a world shaped like a top and not much wider than the Empire State Building. Bennu’s extremely weak gravity and treacherous, boulder-covered surface pushed the spacecraft and its team to their limits. To descend to the asteroid’s surface, the spacecraft needed to switch to backup navigation software mid-mission, and engineers had to model even the slightest forces that might push OSIRIS-REx off-course, such as the pressure of sunlight itself. (Find out more about the historic OSIRIS-REx mission.)
Launched in 2016, OSIRIS-REx orbited Bennu from New Year’s Eve 2018 until just nine days ago, mapping the asteroid’s surface and studying its mineral makeup. On October 20, the spacecraft finally made the plunge, dodging building-size boulders to touch down within a patch of crater floor about the size of two parking spots nicknamed Nightingale, one of many landmarks on Bennu named for birds. (The asteroid itself is named for an ancient Egyptian heron deity.)
OSIRIS-REx’s sample-collection device took over from there. Resembling a Roomba vacuum on the end of a 10-foot-long pogo stick, the device pressed two inches into Bennu’s surface and then fired a bottle of pressurized nitrogen gas. The blast made a dent in the ground more than a foot and a half deep.
As debris blew into space, a series of screens inside the TAGSAM device ensnared some of it to bring home to Earth. These incoming particles passed through a barrier, kind of like a mylar doggie door, as they entered the TAGSAM’s head. This flap should have secured the particles within the device, but TAGSAM picked up several big clods of space dirt, larger than an inch wide, that jammed part of the flap open.
On October 22, personnel at Lockheed Martin Space in Littleton, Colorado, home of OSIRIS-REx mission support, received images from the spacecraft that revealed an estimated several dozen grams of the Bennu sample had drifted off.
“Basically, it’s like a saltshaker,” Lauretta said.
Thankfully, this leak doesn’t appear to have jeopardized the mission. As of October 27, images of TAGSAM’s head confirmed that the device is holding at least 400 grams of material, and maybe much more, Lauretta said. In lab experiments with a replica of the TAGSAM device, scenarios that most closely resembled the October 20 event trapped at least 1,200 grams of debris. “There’s a high probability that the TAGSAM head was as full as it possibly could have been,” Lauretta said.
With the door open, a technician at Kennedy Space Center inspects the inside of the sample return capsule, circular object at right, in 2016 during testing of the door. The leaking sampling head was placed inside this capsule for its journey back to Earth.
Photograph by Kim Shiflett, NASAThe spacecraft is slated to begin its cruise back to Earth in March 2021. In September 2023, once it flies by our home planet, it will drop its capsule—and the precious cargo within—into the Utah desert. Only then will researchers know for sure how much mass the spacecraft sampled. Plans for OSIRIS-REx after it drops off the sample haven’t been finalized, but the spacecraft should be healthy enough to continue exploring the solar system for years to come.
“All that we have left to do to deliver on our promise to [NASA] is get that sample safely back to Earth,” Lauretta said in an October 21 media briefing, “get it into our laboratories, and answer the fundamental questions about the formation of our solar system and why Earth is a habitable world.”