O-REx Ready for Its Big Day — Grabbing a Sample of Asteroid Bennu

NASA’s OSIRIS-REx spacecraft will make its first attempt to grab a sample of asteroid Bennu tomorrow.  The spacecraft has been orbiting Bennu for almost two years assessing the asteroid and the best place to touch down. If all goes well, this will be the only attempt, but if not, it can try twice more.

Bennu, named after an ancient Egyptian mythological bird by a 9 year-old boy from North Carolina in a 2013 NASA “Name the Asteroid” competition, is basically a pile of rubble left over from the formation of the solar system. That’s just what NASA was looking for, a remnant of the early solar system that holds clues to what was taking place at that time including the evolution of life.

The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx or O-REx) spacecraft is equipped with scientific instruments to study Bennu remotely, but nothing can compare with bringing back samples that can be studied in Earth-based labs with even better equipment.

Launched on a United Launch Alliance Atlas V rocket in 2016, O-REx arrived at Bennu on December 3, 2018, almost two years ago.  Since then it has been studying the asteroid and scouting out the best place to collect a sample.

Scientists had studied Bennu from Earth, but were surprised to discover the surface was completely different than expected. As deputy principal investigator Heather Enos from the University of Arizona explained at a media teleconference today, there were no big sandy beaches for O-REx to do its job.

Instead, the surface is very rough and full of large boulders, forcing mission managers to study high resolution images taken by O-REx to pick the best place to get a sample with high scientific value. That turned out to be an area they named Nightingale which, based on imagery, has a lot of material that is less than 2 centimeters (just under an inch) in size, the largest the spacecraft can ingest.

Nightingale is, however, only 16 meters (52 feet) in diameter and surrounded by building-sized boulders. Ken Getzandanner, O-REx flight dynamics officer at NASA’s Goddard Space Flight Center, said today the original requirement was for O-REx to have 25 meter accuracy when it touched down, but they needed to improve that once they realized what the surface was like. They did and now it can land with 7-meter precision.

Two test runs were made earlier this year. Tomorrow will be the first attempt to actually collect a sample.

At a distance of 334 million kilometers (207 million miles) from Earth, it takes a radio signal 18.5 minutes to make the trip to Lockheed Martin’s control center near Denver, CO.  Lockheed Martin Space built the spacecraft and mission control is located there.

The spacecraft itself can decide to abort the attempt if it senses an unknown hazard.

At 6:12 pm EDT Earth-receive time tomorrow, the O-REx team will know if the spacecraft successfully executed its “Touch-and-Go” (TAG) maneuver.  The asteroid has almost no gravity, so it is not possible to land.  Instead, O-REx basically “kisses” the surface with its TAG Sample Acquisition Mechanism (TAGSAM), which has a sample head at the end of an articulated arm.

When TAGSAM senses it touched the surface, nitrogen gas will be expelled from a canister to stir up dust that then is vacuumed into the sample head. Three nitrogen canisters are on board, so three attempts can be made if needed, though the hope is that it will take just one try.

University of Arizona’s Dante Lauretta is the Principal Investigator (PI) of the O-REx mission.  He and the rest of the O-REx team will not know if a sample was indeed acquired until next week. On October 22, an on-board camera will take images of the TAGSAM head to see if samples are visible and on October 24, mission controllers will spin the spacecraft and measure its moment of inertia to determine if the mass of the spacecraft increased. The plan is to obtain at least 60 grams (0.13 pound or 2 ounces) of material, but 2 kilograms (4.4 pounds) is a stretch goal.

If the answer is yes, the samples will be transferred to O-REx’s sample return canister and the spacecraft will be readied for the trip back to Earth.  If not, it will try again, probably at a backup site named Osprey no earlier than January 2021.

O-REx is scheduled to depart Bennu in 2021, with the sample return canister landing in the Utah desert on September 24, 2023.

This is NASA’s first attempt to bring an asteroid sample back to Earth, but it already has returned samples of dust from a comet (Stardust in 2006) and the solar wind (Genesis in 2004). The Japan Aerospace Exploration Agency (JAXA) returned over 1,000 grains of asteroid Itokawa in 2010 on the Hayabusa mission, and Hayabusa2 is bringing back samples of asteroid Ryugu right now. Its sample return canister will land in Woomera, Australia on December 6, 2020.  JAXA and NASA are closely cooperating on their asteroid sample return missions.

NASA has had several missions to visit asteroids in the past, with more coming up. The Lucy mission will visit the Trojan asteroids that share Jupiter’s orbit around the Sun.  Psyche is headed to a unique asteroid between Mars and Jupiter.  The Double Asteroid Redirection Test (DART) is a planetary defense mission that will visit Didymos, a binary asteroid — two objects orbiting each other — and use a kinetic impactor to try to change the orbit of the smaller object to demonstrate a technique that might be used in the future if an asteroid threatens Earth. Lucy and DART are scheduled for launch next year, Psyche in 2022.

But O-REx is the only NASA mission that will return an asteroid sample to Earth.