October 20, 2020

— A NASA spacecraft has played "tag" with an asteroid in an attempt to come away with a cache of pebbles as its prize.

The OSIRIS-REx robotic probe completed its first Touch-And-Go (TAG) sample collection at the small asteroid Bennu on Tuesday (Oct. 20). The maneuver marked only the third time in history and first time for NASA that a spacecraft has tried to collect soils and rocks from an asteroid after two previous sample return missions launched by Japan.

"I can't believe we actually pulled this off!" exclaimed Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, after confirmation was received that the TAG maneuver was complete at Bennu. "This is history, this is amazing."

OSIRIS-REx, or Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer, touched "Nightingale," a rocky area in the northern hemisphere of Bennu, for about six seconds on Tuesday using its robotic arm. The probe's touch-and-go sample acquisition mechanism fired a burst of nitrogen gas to stir up and lift the asteroid's soil into its collector head. The spacecraft then fired its thrusters to back away from Bennu's surface and navigate to a safe distance from the asteroid.

If the collection was successful — to be determined by photos taken on Thursday (Oct. 22) and a mass measurement two days later — then OSIRIS-REx will return the samples to Earth on Sep. 24, 2023. If not, a second attempt at the backup site "Osprey" will be made on Jan. 12, 2021.

OSIRIS-REx sample collection. Click to enlarge video in new, pop-up window. (NASA)

Four years to four hours

Launched on Sept. 8, 2016, OSIRIS-REx orbited the sun for a year and then swung around Earth to align its trajectory with that of its destination. The spacecraft arrived at Bennu on Dec. 8, 2018 and entered orbit three weeks later.

For almost two years, OSIRIS-REx conducted a detailed survey of the asteroid, revealing a much more rugged, boulder-strewn surface than had been expected and particle plumes actively erupting from the small world. After identifying Nightingale as its target touchdown site, the spacecraft performed two approach rehearsals.

(Nightingale was named native Egyptian bird, complementing the mission's two other naming conventions, Egyptian deities for the asteroid and spacecraft and mythological birds for surface features on Bennu.)

On Tuesday, OSIRIS-REx began its 4.5-hour-long sample collection attempt at 1:50 p.m. EDT (1750 GMT). The sequence started with the spacecraft firing its thrusters, initiating its descent from 2,500 feet (770 meters) above Bennu. About four hours later, the probe performed a "Checkpoint" maneuver at approximately 410 feet (125 m) from the asteroid, adjusting its position and speed for a steep dive to the surface.

OSIRIS-REx then conducted a "Matchpoint" burn at about 177 feet (54 meters), slowing its descent and targeting a path to match the asteroid's rotation at the time of contact. Descending to the surface, it touched down within a 52-foot-wide (16-meter) area at Nightingale at about 5:53 p.m. EDT (2153 GMT).

As the spacecraft and Bennu were approximately 207 million miles (334 million km) from Earth at the point of the TAG, it took another 18.5 minutes for the signals confirming the touchdown to reach the mission team. Images and science data collected during the approach and touchdown will be downlinked after the probe can point its primary antenna back to Earth to transmit at higher communication rates.

Batch of Bennu

NASA's goal for the OSIRIS-REx mission is to collect at least 2 ounces (60 grams) of Bennu's rocky material to bring back to Earth — the largest sample return from a celestial body since the moon rocks were brought back by the Apollo astronauts.

Japan's first asteroid sample mission, Hayabusa, returned microscopic particles from the rocky body Itokawa in 2010. The country's follow-up mission, Hayabusa 2, is now on its way back from asteroid Ryugu with the results of two sample collection attempts. The Hayabusa 2 return capsule is expected to land on Dec. 6 in the Australian outback. NASA and Japan have an agreement to share samples for scientific comparison and study.

"The best outcome would be we collect a massive sample," said Heather Enos, OSIRIS-REx deputy principal investigator at the University of Arizona, Tucson. "We have the capability of collecting up to 2 kilograms [4.4 pounds] and I would love for that capsule to be completely full."

Bennu was chosen for the OSIRIS-REx mission because of its composition, size and proximity to Earth (it is projected to pass close to Earth, within the orbit of the moon, in 2135). Bennu is a B-type asteroid (primitive and carbon-rich), which has organic compounds and water-bearing minerals like clays.

"We want something that represents Bennu's signatures of carbon-rich and hydrated materials," said Enos, talking about the nature of the samples collected. "I would hope we have a couple of different sizes of distribution. I would love tiny grains and I would like a couple at the maximum of 2 centimeters (0.78 inches) that [the collector] can ingest. Diversity is the key to being able to get the most out of that sample."

This article was updated Oct. 21 to add imagery from the sample collection event and specify the amount of time that OSIRIS-REx was in contact with Bennu.