December 5, 2020

NASA’s OSIRIS-REx spacecraft lands on asteroid in bid to collect samples


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Artist’s illustration of the OSIRIS-REx spacecraft touching down on asteroid Bennu. Credit: NASA/Goddard/CI Lab

A robotic arm extended from NASA’s OSIRIS-REx spacecraft briefly contacted the rugged surface of asteroid Bennu Tuesday to gobble up pristine samples, a climactic moment in the $1 billion mission to bring asteroid material back to Earth in 2023.

The daring touch and go landing was the first attempt by a U.S. spacecraft to collect a sample from an asteroid. Once the specimens are back on Earth, scientists hope to learn more about the origin and evolution of the solar system.

The materials could provide clues about how water and the seeds of life made their way to Earth.

Signals racing across a 207-million-mile (333-million-kilometer) gulf between Bennu and Earth reached OSIRIS-REx mission control at 6:12 p.m. EDT (2212 GMT), confirming the spacecraft gently touched down on the airless asteroid after a glacial final descent at just 0.2 mph (10 centimeters per second).

Cheers erupted at the Lockheed Martin control center near Denver, where scientists and engineers tracked OSIRIS-REx as it moved in for an automated touch and go landing. Navigation algorithms on-board the spacecraft safely guided OSIRIS-REx to an on-target touchdown within a predetermined zone the size of a tennis court, avoiding a craggy 23-foot-tall (7-meter) nearby boulder that scientists dubbed “Mount Doom.”

Moments later, telemetry data from the spacecraft confirmed its sampling mechanism — known as the TAGSAM — fired a bottle of high-pressure nitrogen gas. The discharge was expected to stir up dust and gravelly material into a sample collection chamber at the end of OSIRIS-REx’s 11-foot-long (3.35-meter) robotic arm.

After spending just seconds on the asteroid’s surface, OSIRIS-REx pulsed thrusters to back away from Bennu. The spacecraft can fly around Bennu with tiny impulses from its rocket engines, thanks to asteroid’s tenuous gravity field.

Preliminary data Tuesday suggested the spacecraft executed the touch and go, or TAG, maneuver as planned.

“The pyro bottles fired,” said Dante Lauretta, OSIRIS-REx’s principal investigator from the University of Arizona. “TAGSAM operated, the back-away thrusters fired, so we’re safely moving away from the asteroid surface. The spacecraft did everything it was supposed to do. So we did it. We tagged the surface of the asteroid.”

Scientists hoped the mission collected at least 2.1 ounces, or 60 grams, of specimens from Bennu. But it will take about a week to confirm how big of a sample OSIRIS-REx scooped up from the asteroid.

“We are on the way to returning the largest sample brought home from space since Apollo,” tweeted NASA Administrator Jim Bridenstine. “If all goes well, this sample will be studied by scientists for generations to come!”

The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer launched from Cape Canaveral in September 2016 aboard a United Launch Alliance Atlas 5 rocket. The Lockheed Martin-built spacecraft reached Bennu in December 2018, and has surveyed the asteroid at centimeter-scale resolution for nearly two years.

The explorer found Bennu was more rugged than scientists expected. Instead of arriving at an asteroid with fields of fine-grained soils, OSIRIS-REx returned images showing Bennu was covered in boulders.

Engineers devised a new way for OSIRIS-REx to navigate around the asteroid using natural feature tracking algorithms. The guidance system compared real-time images from the spacecraft’s navigation cameras to a topographic map loaded into the on-board computer, allowing OSIRIS-REx’s autopilot control system to determine its location and avoid contacting dangerous hazards.

“We have overcome the amazing challenges that this asteroid has thrown at us, and the spacecraft appears to have operated flawlessly,” Lauretta said on NASA TV’s broadcast of the touch and go landing. “We made it down to the asteroid surface. We were in contact. The gas bottles fired.”

The spacecraft was expected to contact Bennu’s surface for 6 to 16 seconds, with its arm outstretched like a pogo stick. The spacecraft climbed away from Bennu, rising back into space over the asteroid’s north pole.

“We don’t know how long we were in contact yet,” Lauretta said. “That’s some reconstructed information that we’re going to have to put together over the next few hours as the data come in. We backed away successfully from the asteroid surface. The team is exuberant back there. Emotions are high. Everybody is really proud, and we have some work to do to determine how much sample that we have collected.”

Once OSIRIS-REx moved to a safe distance from the asteroid, the spacecraft was scheduled to contact mission control with its high-gain antenna. That will speed up the flow of data streaming down from the spacecraft, which was broadcasting low-rate telemetry during the critical moments of the touch and go landing.

Ground teams are eager to see pictures captured by SAMCAM, a close-range camera designed to monitor the sampling maneuver and see if any asteroid materials made it inside the collection chamber.

“Those SAMCAM images are going to tell us an enormous amount of information about how the events of today went,” Lauretta said. “We’re going to be looking at a whole series of images as we descended down to the surface, made contact, fired that gas bottle, and I really want to know how that surface responded.”

If the surface appears scarred, the nitrogen discharge likely disrupted the asteroid material enough to force some of it into the spacecraft’s sampling mechanism.

“We haven’t done this before, so this is new territory for us, and the whole science team, I know, is really looking forward to that information,” he said. “For one thing, it’ll tell us the likelihood of sample collection, kind of a probabilistic assessment. There will probably be a lot of science that comes out of that as well.”

NASA plans to release images from the sampling attempt Wednesday, once the pictures are beamed back to Earth and processed.

“Kudos to the team,” Lauretta said Tuesday. “It’s an amazing experience. History was made tonight.”

On Saturday, controllers are scheduled to command OSIRIS-REx into a spin maneuver to measure its moment of inertia. Engineers will compare the results to a similar maneuver before the sampling run, yielding an estimate of how much mass the spacecraft grabbed from Bennu.

The mission’s requirement was to retrieve at least 2.1 ounces, or 60 grams, of material from the asteroid. But scientists hoped OSIRIS-REx could collect much more, perhaps as much as 4.4 pounds, or 2 kilograms, of pebbles and dust grains.

If managers are satisfied OSIRIS-REx has gathered at least 60 grams of samples, NASA will call it a success and prepare the spacecraft to begin its return journey to Earth next March. If not, the spacecraft could try another touch and go landing as soon as January to snatch up more asteroid material.

OSIRIS-REx is scheduled to release its return capsule to parachute to a landing in the Utah desert on Sept. 24, 2023.

Shaped like a spinning top, Bennu measures around a third of a mile (500 meters) in diameter and rotates once on its axis every 4.3 hours. Named for a bird-like ancient Egyptian deity linked with the sun, creation and rebirth, Bennu follows a path around the sun that intersects Earth’s orbit, and the asteroid makes a relatively close approach to Earth once every six years.

That makes Bennu a potentially hazardous asteroid, and it poses a low threat of eventually hitting Earth. There is a 1-in-2,700 chance of Bennu impacting Earth in the late 2100s.

Bennu was discovered in 1999 by a survey with a ground-based telescope searching for near-Earth asteroids. OSIRIS-REx is the first mission to visit Bennu.

Since arriving at Bennu nearly two years ago, OSIRIS-REx has determined the asteroid is shedding material into space. The mission has also found that Bennu — known as a B-type asteroid — is covered in carbon-rich, water-bearing minerals. The organic material may contain carbon in a form often found in biology or in compounds associated with biology, scientists announced Oct. 8.

“The abundance of carbon-bearing material is a major scientific triumph for the mission,” Lauretta said earlier this month. “We are now optimistic that we will collect and return a sample with organic material — a central goal of the OSIRIS-REx mission.”

In a press release accompanying the announcement of the new scientific data earlier this month, NASA described Bennu as a “diamond-shaped pile of rubble floating in space.”

Data from NASA’s OSIRIS-REx spacecraft was used to create this shape model of asteroid Bennu at 75-centimeter resolution. Credit: NASA/Goddard/University of Arizona

Scientists said OSIRIS-REx’s targeted touchdown site — dubbed “Nightingale” — also harbors the signature of organic materials, the building blocks of life. The Nightingale location on Bennu’s northern hemisphere is situated inside inside a 460-foot (140-meter) crater, but the area deemed safe for the spacecraft to touch is 52 feet (16 meters) across.

The spacecraft’s solar panels extend more than 20 feet, or 6.2 meters, tip-to-tip.

“It’s kind of a tight fit,” Lauretta said earlier this year.

But scientists expect Nightingale to provide a rich return. Observations from OSIRIS-REx also indicate the material at the touch and go was only recently exposed to the harsh environment of space, meaning the mission could snag pristine samples that have been undisturbed for most of the solar system’s 4.5 billion-year history.

OSIRIS-REx’s descent toward Bennu on Tuesday lasted more than four hours from the time it left its orbit around the asteroid.

After commencing its descent, the spacecraft extended the TAGSAM sampling arm and moved closer to the asteroid. In the final hour before touchdown, OSIRIS-REx turned to point its sampling arm and navigation cameras toward Bennu, then moved its two solar array panels into a “Y-wing” configuration above the craft’s main body, ensuring the wings did not hit the asteroid’s surface.

Two more maneuvers — known as the checkpoint and matchpoint burns — began the terminal descent phase and slowed the spacecraft’s approach to the asteroid to a fraction of a walking pace.

The mission’s sampling mechanism — about the size of a dinner plate — was expected to scour up bits of dust and rock from as deep as 8 inches (20 centimeters) beneath Bennu’s surface, where material should be shielded from wild temperature swings that could damage sensitive organics.

Invented by a Lockheed Martin engineer, the TAGSAM nozzle is designed to trap samples blown away by nitrogen gas and suck them into a collector with a rush of air, similar to a reverse vacuum cleaner.

“The best outcome would be that we would collect a massive sample,” said Heather Enos, OSIRIS-REx’s deputy principal investigator at the University of Arizona, before the sample collection attempt. “We say we have a requirement for 60 grams, or 2 ounces, but we have the capability of collecting up to 2 kilograms. I would love for that capsule to be completely full.”

NASA has set Oct. 30 for a key decision point on whether to declare success, or continue planning for another sampling run at a different site on Bennu.

This illustration shows the relative sizes of asteroid Bennu, the Empire State Building, and the Eiffel Tower. Credit: NASA/Goddard/University of Arizona

Once they are confident the spacecraft has the asteroid samples, ground controllers will send commands for the TAGSAM arm to place the collection canister inside OSIRIS-REx’s landing capsule. Explosive bolts will sever the TAGSAM head from the craft’s robotic arm, and the capsule’s lid will close over the device for the trip home.

After OSIRIS-REx’s return carrier lands back on Earth, a recovery team will transport the craft to NASA’s Johnson Space Center in Houston, where scientists will open the canister inside a pristine sample curation laboratory and begin studying its contents.

Researchers at Johnson’s astromaterials lab also analyze rocks returned from the moon by the Apollo astronauts.

Enos said scientists hope for asteroid materials that “represent Bennu’s signatures of carbon-rich and hydrated minerals. That would be amazing, and I have every reason to believe that that’s going to be in that sample.”

“In terms of the size distribution, I would hope that we have a couple of different size distributions. I would like tiny grains. I would like a couple almost at the maximum 2 centimeters that we can ingest,” Enos said Monday. “So diversity is key to be able to get the most out of the sample. That is what my money is on tomorrow.”

The team that developed and built the OSIRIS-REx spacecraft took extra measures to ensure the asteroid sample will not be contaminated by organic materials from Earth.

Researchers will use optical and electron microscopes, super-computing labs, and synchrotron accelerators — instruments the size of a large room or a building — in their asteroid sample analysis.

Scientific equipment qualified to fly in space have to operate in extreme temperatures, an airless vacuum, and intense radiation, all while functioning on very little power.

Scientists will attempt to determine the chirality, or handedness, of amino acids and other compounds grabbed from Bennu. Molecules associated with life, such as DNA, have a distinctive orientation. In the case of DNA in organisms on Earth, the double helix always twists in a right-handed direction, and the atoms that make up amino acids in biology are almost always left-handed.

The preference for a left or right orientation among the atoms making up biological molecules makes it easier for chemicals to latch together and build more complex structures.

“Bennu is one of over a million known asteroids in our solar system, and these asteroids are relics of that earliest material that formed the planets in the solar system, and they hold the key information to unlocking how the solar system formed, and how it evolved over time,” said Lori Glaze, director of NASA’s planetary science division.

Data from OSIRIS-REx’s surveys of Bennu show many of the asteroid’s darkest boulders are weaker and more porous than expected. Scientists say most of the boulders on the asteroid are too weak to survive entry into Earth’s atmosphere, so the specimens targeted by OSIRIS-REx could offer a “missing link” because similar rocks are not well represented in meteorite collections.

“Returned samples from Bennu could help us answer some key astrobiology questions, such as how water and organic materials were delivered to Earth, and the role those key ingredients played in the early initiation of life on Earth,” Glaze said.

Another objective of the OSIRIS-REx mission is to characterize the forces pushing on Bennu and gradually changing its orbit. One of the forces is called the Yarkovsky effect, in which thermal emissions from an asteroid can alter its trajectory through the solar system. Solar radiation pressure is another influence on asteroid orbits.

That data will help scientists better predict when asteroids might threaten Earth.

While it is the first U.S. asteroid sample return probe, OSIRIS-REx is not the only spacecraft currently traveling the solar system on a mission to retrieve materials from an asteroid and bring them back to Earth.

Japan’s Hayabusa 2 spacecraft is on course to bring home samples from asteroid Ryugu on Dec. 6, capping a six-year expedition in space. The mission captured bits of rock from two locations on the half-mile-wide (900-meter) asteroid last year.

Like Bennu, Ryugu is an asteroid rich in carbon and organics.

NASA and the Japan Aerospace Exploration Agency have agreed to share Hayabusa 2 and OSIRIS-REx samples with scientists in each country.

“We have an exchange of scientists working on both missions, and of course, we’ll be exchanging portions of each other’s samples so we that we can maximize the science,” Glaze said.

“We believe (JAXA had) a very successful attempt, and they expect to bring back material, but our hope is with OSIRIS-REx, we’ll be collecting significantly more mass of samples, she said. “So between the two of them, we should have an excellent combination of samples to study.”

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Follow Stephen Clark on Twitter: @StephenClark1.


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