Tenacity, triumph and discovery: Looking back at OSIRIS-REx at mission's end
By Mikayla Mace Kelley, University Communications
A triptych of major moments of NASA's U of A-led OSIRIS-REx mission, including launch, the Touch-And-Go maneuver to collect a sample and the mission principal investigator Dante Lauretta celebrating a successful sample return.
Joel Kowsky/NASA; NASA/Goddard/University of Arizona; and Chris Richards/University Communications
Sept. 30 marked the formal end of NASA's OSIRIS-REx mission. This was the United States' first ambitious attempt to collect a sample of an asteroid and return it to Earth, and it was led by the University of Arizona.
In the more than two decades since its inception, the mission overcame several challenges to accomplish unprecedented feats of exploration and science.
In a letter of thanks and congratulations to his team, mission principal investigator Dante Lauretta, Regents Professor and director of the Arizona Astrobiology Center, reflected on a sentence from a report submitted to NASA at the mission's end: "Successful exploration missions are not those that avoid surprises, they are those that are deliberately designed to adapt to them."
"That certainly describes OSIRIS-REx," Lauretta said. "Again and again, the mission presented us with circumstances we had not expected, and again and again, this team found a way forward. I feel enormous pride in what we accomplished together, and real sadness that this journey has come to an end… It has been the privilege of my professional life to serve as principal investigator of OSIRIS-REx."
A dream made material
Where did we come from? How did we come to exist? What's the origin of the organic material that provided the building blocks that led to life? These were the deep questions that the late Michael Drake wanted answered when he first proposed the mission in 2004. At the time, Drake was the director of the Lunar and Planetary Laboratory.
The tenacity that characterizes OSIRIS-REx team today was evident even then: NASA denied the proposal – twice – before greenlighting what would become the billion-dollar mission under the New Frontiers Program in 2011.
Former LPL director Michael Drake and current OSIRIS-REx principal investigator Dante Lauretta in 2008.
University of Arizona
Drake led the team with Lauretta serving as deputy principal investigator. But, when Drake died only months after mission selection, Lauretta – still an early-career scientist – stepped into Drake's shoes. Ever since, he has seen the team through each of its successes.
Drake and Lauretta designed OSIRIS-REx to reveal mysteries about the formation and evolution of the solar system, the origins for the ingredients of life and to inform planetary defense. They selected Bennu – an asteroid slightly wider than the height of the Empire State Building – as the target asteroid for three reasons: the near-Earth asteroid was accessible and had a small chance of impacting the Earth late in the 22nd century, it spins at a rate reasonable enough to approach by spacecraft, and is rich in organic material, the building blocks of life as we know it.
Such lofty goals required the power of precision instruments. These include a suite of three cameras developed by the U of A, called OCAMS, which were designed to support the mission through all of its phases; spectrometers that provide light, mineral and temperature information; the Touch-And-Go Sample Acquisition Mechanism to gather the pieces of Bennu; and the Sample Return Capsule, outfitted with a heat shield and parachutes to deliver the sample safely to Earth.
By the time it was completed, OSIRIS-REx measured 20 feet long with its solar panels deployed and about 8 feet wide, about the size of a 15-passenger van, and weighed 4,650 pounds with fuel.
Getting to know Bennu
The spacecraft launched from Cape Canaveral aboard an Atlas V rocket on Sept. 8, 2016.
An Atlas V rocket lifts off from Space Launch Complex 41 at Cape Canaveral Air Force Station carrying NASA’s OSIRIS-REx spacecraft on the first U.S. mission to sample an asteroid and return it to Earth for study.
NASA/Sandy Joseph and Tim Terry
At the start of its two-year journey, Bennu was still just a point of light in a telescope, but based on analysis of its reflected light, the science team predicted it would be shaped like a spinning top and have a surface coated in beach-like sand.
Upon arrival on Dec. 3, 2018, the team learned they had accurately predicted the asteroid's shape, but Bennu held two major surprises: First, rather than sand, it was an amalgamation of rocks and boulders. This posed a significant challenge because the spacecraft was specifically designed to capture dust and small rocks. Second, it was flinging material into space. After closer investigation, the team found that most of the ejected material fell back onto the asteroid and the likelihood of debris striking the spacecraft was minimal.
For 18 months, OSIRIS-REx circled its target to survey its surface.
Guinness World Records recognized the mission for two record-breaking accomplishments: The spacecraft made the closest orbit of a planetary body and made the asteroid the smallest planetary object ever orbited by a spacecraft.
But such maneuvers were not just for impressive feats of agility, OSIRIS-REx was capturing very fine resolution images – down to 3 millimeters per pixel at some locations – to create a 3D map and identify a sample site, if one could be found among its rough and rugged terrain.
"Our expectations about the asteroid's surface were completely wrong," Lauretta said. "There was no obvious place to collect a sample anywhere."
In December 2019, the mission homed in on Hokioi Crater as the primary sample collection site, dubbing it "Nightingale." According to Lauretta, it contained the greatest amount of fine-grained material and – compared to other potential sites – it was relatively accessible.
Well before any rocks sat under a microscope, the science team was publishing science results. They discovered that the asteroid was covered in organic material and that the rocky debris covering the Nightingale sample site had only recently been exposed, both findings ensured that the sample contained some of the most pristine material available.
Touching an asteroid
Only months before the spacecraft was scheduled to execute the precarious task of sample collection, the COVID-19 pandemic swept across the globe.
But, on Oct. 20, 2020, right on schedule, the spacecraft unfurled its Touch and Go Sample Acquisition Mechanism, TAGSAM for short, to briefly touch the asteroid's surface. It captured gravel and dust so loosely bound that the spacecraft momentarily dipped into the asteroid, like a child jumping in a ball pit, before firing its thrusters to escape.
An illustration showing how the OSIRIS-REx spacecraft impact asteroid Bennu's surface when it touched down and collected a sample.
NASA's Goddard Space Flight Center Conceptual Image Lab
While this moment was scary, it provided valuable information. Bennu's surface acted more like a fluid than a solid. It's possible that asteroids like Bennu, barely held together by gravity or electrostatic force, could break apart in Earth's atmosphere and pose a different type of hazard than solid asteroids.
The drama didn't end there. Not long after sample collection, the team realized that rocks were propping open the mylar flap, causing the spacecraft to leak what precious material it had collected.
Their response was quick and definitive. They paused the spin maneuver designed to reveal the sample mass and instead deposited the TAGSAM head, which held the material, directly in the into the Sample Return Capsule. Eight days after TAG, the mission successfully stowed the sample.
On May 10, 2021, the spacecraft fired its main engines at full throttle for seven minutes to begin its return cruise.
The more than two-year trip home provided ample time for science. In August 2021, the team published findings based on Bennu tracking data. They found that the asteroid has an increased risk of impacting Earth than thought. This work also improved our ability to predict orbits of many other asteroids.
They also found that Bennu's impact probability through the year 2300 to be about 1 in 1,750 and identified Sept. 24, 2182 as the most significant single date, with an impact probability of 1 in 2,700. Although the chances of hitting Earth are low, Bennu is still one of the most hazardous known objects in the solar system.
Homecoming
On the morning of Sept. 24, 2023, after seven years in space and 4 billion miles traveled, the spacecraft deployed the Sample Return Capsule for delivery to the Utah desert. As it plunged through the atmosphere, the team realized something wasn't right. In a nail-biting turn of events, one parachute did not deploy. Luckily, the main chute did, and within several minutes, the recovery team was dispatched to the landing site. They found the capsule blackened from reentry, but otherwise in good shape.
From left to right, NASA sample return capsule science lead Scott Sandford, NASA astromaterials curator Francis McCubbin and U of A's OSIRIS-REx principal investigator Dante Lauretta, collect science data shortly after the sample return capsule landed in the Utah desert.
NASA/Keegan Barber
"It was like seeing an old friend that you hadn't seen for a long time," Lauretta said during a post-landing press conference hosted by NASA.
The sample was handled with extreme care from reentry to opening, ensuring that the sample remain as pristine as possible.
Back in space, only twenty minutes after dropping the sample high above Earth's atmosphere, the spacecraft fired its thrusters to put it on course to rendezvous with Apophis in five-and-a-half years – just after that asteroid makes its own close approach to Earth.
The start of science
On Sept. 26, 2023, the capsule was opened for the first time. Only a few weeks later, NASA announced that from preliminary results, they found significant quantities of carbon-based compounds and hydrated minerals, supporting hypotheses about the potential role of asteroids in bringing essential components for life to early Earth.
A few days after that, the mission was able to confirm that they successfully acquired 121.6 grams, or 4.3 ounces, of sample, more than twice mission requirements. By December NASA began distributing pieces of Bennu, and sample science began at the U of A. Here, scientists are able to probe the samples, down to a single atom.
Lauretta has often said that decades of research will come from this mission, but so much has already been gleaned from this immense effort.
The asteroid Bennu up close. The surface was covered in rocks and boulders, surprisingly.
NASA/University of Arizona/CSA/York University/MDA
For example, Bennu was surprisingly craggy because of the highly porous nature of its rocks. Impacts weren't fragmenting Bennu's rocks like they expected. Rather, impacts were compressing the pores within the rocks. What's more, it was these pores, in addition to unexpected cracks only detected once samples were Earth-bound, that hoodwinked scientists into mistakenly inferring that that Bennu would be sandy. This is because sandy material heats up and cools down rapidly, such like Bennu seemed to be doing.
They also discovered that Bennu originated from a larger parent asteroid that broke up after a collision, likely from the asteroid belt between Mars and Jupiter. The parent asteroid consisted of material with diverse origins – near the sun, far from the sun and from the stardust that existed even before the sun. This all coalesced more than 4 billion years ago as our solar system was forming.
Life's building blocks
They also learned that the parent body was also likely water-rich.
"Fluids altered rock at low temperatures and later evolved into concentrated brines that precipitated carbonates, phosphates, sulfates, chlorides, fluorides and other secondary minerals," Lauretta said. "Individual Bennu stones record different alteration histories, showing how heterogeneous those processes were even over centimeter scales."
This finding also provocatively suggests that the building blocks of life were widely distributed across the solar system, delivered to Earth by asteroids like this. And these findings are only beginning to scratch the surface of Drake's initial, provocative questions that launched this daring mission.
At mission's end, the science team has published more than 200 research papers, and this is only the beginning.
"Most of the Bennu material will remain in curation for future generations, to be studied with questions and instruments we cannot yet anticipate," Lauretta said.
Now the spacecraft flies on. Not only has it been reincarnated as OSIRIS-APEX, which is on its way to study another near-Earth asteroid, Apophis, but many of the early-career scientists and students who worked on OSIRIS-REx are leading the APEX team into the next generation of scientific discovery.
