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Touch, go: NASA prepares for spacecraft’s 10-second grab from asteroid

The chunk of rock that is the asteroid Bennu, as seen by OSIRIS-REx spacecraft
The asteroid Bennu, as seen by NASA’s OSIRIS-REx spacecraft. After circling the asteroid for almost two years, the craft will attempt to collect a handful of the asteroid’s rubble.
(NASA / Goddard / University of Arizona / CSA / York / MDA via Associated Press)

After almost two years circling an ancient asteroid hundreds of millions of miles away, a NASA spacecraft is ready to attempt a descent to the treacherous, boulder-packed surface so it can snatch a handful of rubble.

The drama is scheduled to unfold Tuesday as the U.S. takes its first crack at collecting asteroid samples for return to Earth, a feat accomplished so far only by Japan.

Brimming with names inspired by Egyptian mythology, the OSIRIS-REx mission is looking to bring back at least 2 ounces of the asteroid Bennu, the biggest otherworldly haul from beyond the moon.

The van-sized spacecraft is aiming for the relatively flat middle of a tennis-court-sized crater named Nightingale — a spot comparable to a few parking spaces here on Earth. Boulders as big as buildings loom over the targeted touchdown zone.

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“The next time you park your car in front of your house or in front of a coffee shop and walk inside, think about the challenge of navigating OSIRIS-REx into one of these spots from 200 million miles away,” said Mike Moreau, NASA’s deputy project manager based at the Goddard Space Flight Center in Maryland.

Once the spacecraft drops out of its half-mile-high orbit around Bennu, it will take a deliberate four hours to descend to just above the surface.

Then OSIRIS-REx’s 11-foot arm will reach out and touch Bennu. Contact should last for five to 10 seconds — just long enough to shoot out pressurized nitrogen gas and suck up the churned dirt and gravel.

The sampling arm of the OSIRIS-REx spacecraft is extended.
The sampling arm of the OSIRIS-REx spacecraft during a practice run in August.
(NASA / Goddard /University of Arizona via Associated Press)
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Programmed in advance, the spacecraft will operate autonomously during the unprecedented touch-and-go maneuver. Since it takes 18 minutes for radio communications to travel between Earth and OSIRIS-REx, ground controllers for spacecraft builder Lockheed Martin near Denver won’t be able to intervene.

If the first attempt doesn’t work, OSIRIS-REx can try again. Any collected samples won’t reach Earth until 2023.

Although NASA has brought back comet dust and solar wind particles, it’s never attempted to sample one of the nearly 1 million known asteroids lurking in our solar system until now. Japan expects to get samples from asteroid Ryugu in December — in the milligrams at most — 10 years after bringing back specks from asteroid Itokawa.

A Japanese spacecraft touched down on a distant asteroid Friday on a mission to collect material that could provide clues to the origin of the solar system and life on Earth.

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Bennu is an asteroid picker’s paradise.

The big, black, roundish, carbon-rich space rock — taller than New York’s Empire State Building — was around when our solar system was forming 4.5 billion years ago. Scientists consider it a time capsule full of pristine building blocks that could help explain how life formed on Earth, and possibly elsewhere.

“This is all about understanding our origins,” said Dante Lauretta of the University of Arizona, the mission’s principal scientist.

There also are selfish reasons for getting to know Bennu better.

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The solar-orbiting asteroid, which swings by Earth every six years, could take aim at us late in the next century. NASA puts the odds of an impact at 1-in-2,700. The more scientists know about potentially menacing asteroids like Bennu, the safer Earth will be.

When OSIRIS-REx blasted off in 2016 for its more-than-$800-million mission, scientists envisioned sandy stretches at Bennu. So the spacecraft was designed to ingest small pebbles less than an inch across.

Scientists were stunned to find massive rocks and chunky gravel all over the place when the spacecraft arrived in 2018. Pebbles were occasionally seen shooting off the asteroid, falling back and sometimes ricocheting off again in a cosmic game of pingpong.

An "X" is superimposed on a spot on the surface of the asteroid.
The X marks the spot where OSIRIS-REx will aim to land on asteroid Bennu. The collection site is named “Nightingale.”
(NASA / Goddard / University of Arizona via Associated Press)
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With so much rough terrain, engineers scrambled to aim for a tighter spot than originally anticipated. Nightingale Crater, the prime target, appears to have the biggest abundance of fine grains, but boulders still abound, including one dubbed Mount Doom.

Then COVID-19 struck.

The team fell behind and bumped the second and final touch-and-go dress rehearsal for the spacecraft to August. That pushed the sample grab to October.

“Returning a sample is hard,” said NASA’s science mission chief, Thomas Zurbuchen. “COVID made it even harder.”

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OSIRIS-REx has three bottles of nitrogen gas, which means it can touch down three times — no more.

If it encounters unexpected hazards such as big rocks that could cause it to tip over, it will back away automatically. There’s also a chance it will touch down safely but fail to collect enough rubble.

In either case, the spacecraft would return to orbit around Bennu and try again in January at another location.

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With the first try finally here, Lauretta is worried, nervous, excited “and confident we have done everything possible to ensure a safe sampling.”


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