Space: OSIRIS-REx successfully touches down on asteroid Bennu, collects samples

Ars Technica said:

NASA scientists confirmed Wednesday that the OSIRIS-REx spacecraft successfully made contact with an asteroid a day earlier, touching the surface for six seconds and collecting dust and pebbles from its surface.

The spacecraft's performance at the asteroid Bennu, which is only about as wide as the Empire State Building is tall, was remarkable. Because the asteroid is so small, its gravity is negligible, which complicates orbital maneuvering by the spacecraft around what is, essentially, a rubble pile.

Despite these challenges, at a distance of 320 million kilometers on Tuesday, NASA engineers and scientists programmed a spacecraft to autonomously touch down within a single meter of its target area.

Newly released images of the encounter show the spacecraft's sampling arm moving toward the asteroid at a speed of 10cm per second and crushing rocks beneath it as it reaches the surface.

"Literally, we crushed it," said Dante Lauretta, principal investigator of the OSIRIS-REx mission. "When the spacecraft made contact, that rock appears to fragment and shatter, which is great news." This is because the "head" of the sampling arm can only collect material less than 2cm in diameter.

Immediately after touchdown, the spacecraft fired a canister of pure nitrogen gas, causing a cloud of material to rise from the surface of the asteroid. The sampling arm lingered on the surface for five more seconds to collect this material before backing away.

Lauretta said the mission team does not yet know how much material the spacecraft collected. If it does not gather at least 60 grams, a second "touch-and-go" maneuver could be performed early next year. But more likely, the spacecraft gathered more than this. As much as 2kg of dust and rocks will be studied back on Earth when a capsule lands in Utah in 2023.

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