December 4, 2020

Asteroid samples sealed in OSIRIS-REx return capsule


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A camera aboard NASA’s OSIRIS-REx spacecraft showed the mission’s sample return capsule closed its heat shield late Wednesday after a robotic arm placed asteroid samples inside for the trip back to Earth. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

A collection chamber that could contain more than 2 pounds of samples gathered from an asteroid in deep space last week has been sealed inside of a return capsule on NASA’s OSIRIS-REx spacecraft to bring the extraterrestrial specimens back to Earth in 2023, officials announced Thursday.

The sample return capsule closed its heat shield to seal up the asteroid specimens late Wednesday, completing steps to place the collection device at the end of a robotic arm inside the module that will protect the rock and soil during re-entry into Earth’s atmosphere.

Mission managers accelerated plans to stow the sample inside the return capsule after finding that asteroid particles were escaping from the collection chamber last week. The OSIRIS-REx spacecraft descended to a precise touch-and-go landing on asteroid Bennu Oct. 20 to gather the surface specimens.

NASA officials announced Thursday that the OSIRIS-REx spacecraft secured the asteroid material inside the sample return capsule more than 200 million miles (330 million kilometers) from Earth.

“We were originally planning to do that stow operation next week, and we’re here to announce today that we have successfully completed that operation,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“This achievement by OSIRIS-REx on behalf of NASA and the world has lifted our vision to the higher things we can achieve together, as teams and nations,” said NASA Administrator Jim Bridenstine in a statement. “Together a team comprising industry, academia and international partners, and a talented and diverse team of NASA employees with all types of expertise, has put us on course to vastly increase our collection on Earth of samples from space.

“Samples like this are going to transform what we know about our universe and ourselves, which is at the base of all NASA’s endeavors,” Bridenstine said in a statement.

Imagery of OSIRIS-REx’s Touch And Go Sample Acquisition Mechanism, or TAGSAM, after the spacecraft’s brief landing on Bennu showed the collection chamber overflowing with material scooped up from the asteroid. The TAGSAM’s 11-foot-tall (3.4-meter) robotic arm contacted Bennu for about six seconds, and the device fired a bottle of compressed nitrogen gas to help blow soil and rock particles into the sampling system.

It turned out the system gathered so much sample that five small rocks jammed into the opening of the collection chamber, preventing its mylar seal from closing. The images of the TAGSAM head last week showed particles escaping, and officials decided to skip plans to move the robotic arm and put the OSIRIS-REx spacecraft into a spin to measure the probe’s moment of inertia, yielding an estimate of how much mass of sample the mission got from Bennu.

Managers worried the robotic arm maneuvers required for the sample mass measurement would cause the TAGSAM head — about the size of a dinner plate — to lose more asteroid material. NASA officials instead elected to stow the sample head into the return capsule as soon as possible.

These images from NASA’s OSIRIS-REx spacecraft were taken Tuesday, Oct. 27, showing the mission’s robotic arm placing the sampling head inside the capsule that will return the asteroid specimens to Earth in 2023. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

NASA’s $1 billion Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer mission launched Sept. 8, 2016, from Cape Canaveral aboard a United Launch Alliance Atlas 5 rocket. OSIRIS-REx’s primary goal is to return asteroid samples to Earth for detailed analysis by scientists, who hope to uncover clues about the origins of the solar system.

The mission requirement was for OSIRIS-REx to gather at least 60 grams, or 2.1 ounces, of asteroid material. Scientists said before the Oct. 20 touch and go landing that the spacecraft could collect much more, and it did.

Data from the brief touchdown on the asteroid indicated the spacecraft’s robotic arm sunk up to 19 inches (48 centimeters) into the Bennu’s soft surface.

Diamond-shaped asteroid Bennu measures about a third of a mile wide and rotates once on its axis every 4.3 hours. Surveys of the asteroid indicate it is rich in carbon and hydrated minerals, two key building blocks of life.

“I am extremely happy with the sample that we’ve collected, and that we intend to bring back to the Earth in September of 2023,” said Dante Lauretta, OSIRIS-REx’s principal investigator from the University of Arizona.

Lauretta said the science team believes it is highly likely the TAGSAM head was at full capacity — about 2 kilograms (4.4 pounds) — with asteroid specimens when the spacecraft fired thrusters to begin backing away from Bennu last week. Scientists believe the sampling system lost “tens of grams” of asteroid material before the TAGSAM head was secured into the sample return capsule Wednesday, Lauretta said.

“I believe we still have hundreds of grams of material in the sample collector head, probably over a kilogram (2.2 pounds easily,” Lauretta said.

That’s well above the mission’s success requirement to bring home 60 grams of asteroid material.

Captured by the spacecraft’s SamCam camera on Oct. 22, 2020, this series of three images shows that the sampler head on NASA’s OSIRIS-REx spacecraft is full of rocks and dust collected from the surface of the asteroid Bennu. They show also that some of these particles are slowly escaping the sampler head. Credit: NASA

Ground teams from Lockheed Martin, which built and operates the spacecraft for NASA, are studying ways to produce a rough estimate of the mass of the asteroid sample. Because managers bypassed the opportunity for a more refined mass estimate, scientists will not know exactly much Bennu material is on-board OSIRIS-REx until the sample return capsule lands on Earth in 2023.

The closure of the sample return capsule’s lid late Wednesday means the mission will not lose any more asteroid samples.

Engineers and scientists at Lockheed Martin’s control center near Denver methodically guided OSIRIS-REx through carefully choreographed procedures to place the TAGSAM head into the return capsule.

The sample head was seated into the capsule’s capture ring Tuesday. Then ground controllers sent commands for the robotic arm pull on the sample head to ensure its latches were well secured.

Telemetry from the spacecraft confirmed the sample head is latched in place, according to NASA.

The next step activated a “tube cutter” to cut lines leading from the sampling device’s nitrogen gas bottles, and fired a separation bolt to sever the TAGSAM head from the robotic arm. Once the sample head was cut from the arm, ground teams sent commands to close the heat shield on the sample return capsule to seal it for the journey back to Earth.

Two latches engaged to firmly close the lid on the heat shield.

Unlike OSIRIS-REx’s touch and go landing — which the spacecraft executed autonomously — the sample stow procedure involved numerous starts and stops, allowing engineers to receive imagery and assess how the operation is going at each major step.

“The reason we’re taking our time is we don’t want to lose those particles,” said Jason Dworkin, OSIRIS-REx’s project scientist at Goddard. “I like to think of every speck we see (escaping) as someone’s PhD being lost. There’s so much information that’s going away.”

The entire process to secure the sample head inside the return capsule took about 36 hours, according to Sandra Freund, OSIRIS-REx’s mission operations manager at Lockheed Martin.

“We had originally thought we’ll do a couple things each day, we’ll work nice working hours, and then we discovered that that was not was not going to be feasible, given the urgency to get the sampler head into the capsule,” Freund said Thursday.

OSIRIS-REx has been slowly backing away from Bennu since the touch and go landing Oct. 20.

Some time between early March and May, the spacecraft will fire its thrusters begin the trip back to Earth. OSIRIS-REx will release the 31-inch-wide (80-centimeter) sample return capsule for a parachute-assisted landing at the Utah Test and Training Range on Sept. 24, 2023.

A recovery team will retrieve the capsule and transport it to NASA’s Johnson Space Center in Houston, where scientists open the container and begin analyzing the asteroid specimens with sophisticated instruments far too large and heavy to carry on a spacecraft.

Touch and go landing revealed asteroid’s soft surface

While the mission’s scientific payoff will wait until the asteroid samples return to Earth, Lauretta said Thursday that scientists are already learning about the physical characteristics of Bennu.

The spacecraft detected small particles flying off Bennu soon after it arrived at the asteroid in December 2018. Those particles appear similar to the flaky material that leaked out of the TAGSAM head.

“It looks like a box of cornflakes out in space,” Lauretta said. “And they’re fluttering around kind of in random motion. They are coming from the TAGSAM head for the most part, but they are colliding with each other. They’re spinning and tumbling. We can resolve many of them.

“So it’s a great imaging calibration data set to better understand the particle ejection events, and the particles trajectories that we observed throughout the entire encounter with the asteroid,” Lauretta said. “Wven though my heart breaks for the loss of sample, it turned out to be a pretty cool science experiment.”

Artist’s illustration of the OSIRIS-REx spacecraft with its sampling arm extended, and the sample return capsule on the lower panel of the vehicle. Credit: NASA

OSIRIS-REx’s contact with the asteroid surface Oct. 20 also provided a rich dataset, suggesting the outer layer of the asteroid’s soil and low-density rocks lacked much cohesion. The spacecraft’s robotic arm touched the asteroid as OSIRIS-REx approached at just 0.2 mph, or 10 centiemters per second, about a tenth the speed of a typical walking pace.

“When the TAGSAM head made contact with the regolith, it just flowed away like a fluid,” Lauretta said. “And I think that’s what would happen to an astronaut if she were to attempt to walk on the surface of the asteroid. She would sink to her knees or deeper — depending on how loose the soil was — until you hit a larger boulder or some kind of bedrock.”

He said the “ground truth” data gathered by OSIRIS-REx will help scientists reexamine models of asteroid geology.

“It’s fascinating that there was so little resistance to the spacecraft from the asteroid surface,” Lauretta said. “Basically, it’s kind of like a ball pit at a kid’s playground. You kind of jump into it and you just sink in.

“Luckily, we had those back-away thrusters to reverse the direction of motion, or we might have just flown all the way through the asteroid,” Lauretta joked.

The fresh measurements of asteroid density from OSIRIS-REx will help scientists refine assessments of the impact risk Bennu might pose to Earth. Scientists have calculated a 1-in-2,700 probability that Bennu might strike Earth in the late 2100s.

Much of the asteroid might burn up in Earth’s atmosphere due to its porosity.

“Thermal analysis indicates that a lot of the material on the surface of Bennu — particularly the large black hummocky boulders which are a major component of the surface — they seem to have material properties that would not survive passage through the atmosphere intact,” Lauretta said. “They would fragment, and much of the material will be lost.”

That means the pristine specimens collected from Bennu are unlike any meteorites or asteroid fragments that have fallen to Earth and reached the surface intact.

Assuming OSIRIS-REx actually scooped up a few pounds of asteroid speciments, scientists could pursue additional experiments on the samples than in OSIRIS-REx’s baseline plan.

NASA will turn over about 25 percent of the sample returned by OSIRIS-REx to scientists for immediate analysis.

The Canadian Space Agency will get 4 percent to reciprocate Canada’s contribute of a laser altimeter instrument to the OSIRIS-REx spacecraft. NASA will provide the Japan Aerospace Exploration Agency with 0.5 percent in exchange for specimens from asteroid Ryugu Japan will give to U.S. scientists from the Hayabusa 2 sample return mission due to land back on Earth in December.

The rest of the material returned by OSIRIS-REx will be stored for future generations of scientists equipped with more advanced laboratory equipment.

“With a baseline sample return, we had 15 grams for analysis,” Lauretta said.

A more massive sample enables new types of experiments.

“The organic chemistry of particular class of compounds called sugars is something we’re very interested in because they play a central role in modern biomolecules,” Lauretta said. “They’re expected to be present at very low abundances, requiring several grams of sample to extract them from. And we thought that would not be feasible with the 15-gram allocation. (That’s) something that does open up with a larger mass available for analysis.”

“We’re trying to understand the formation of the solar system, the formation of the Earth, and the delivery of key volatiles like water and organic material that made our planet habitable early in its history,” Lauretta said.

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Follow Stephen Clark on Twitter: @StephenClark1.


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