0253 GMT October 24, 2020
Four years into its seven year mission, NASA’S OSIRIS-REx spacecraft is finally set to make a quick “touch-and-go” (TAG) onto the surface of a planetary relic that likely formed within the first ten million years of our Solar System’s history.
Tuesday’s attempt to touch the surface of the rubble pile asteroid ‘101955 Bennu’ marks NASA’s first effort at an asteroid sample return. However, the hugely successful Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission has already garnered Guinness World Records for both the smallest object ever orbited and the closest orbit of a planetary body by a spacecraft.
If successful, Tuesday’s attempt will garner at least 2.1 ounces (60 grams) of surface material from the 1614-foot diameter asteroid before the spacecraft begins its three-year journey back to Earth.
“The sample was an eye-witness to the formation of the Solar System [some 4.56 billion years ago] and analyzing it should give insight into the processes present at the dawn of the Solar System, of planets, and of life,” Jason Dworkin, the mission’s project scientist at NASA’s Goddard Space Flight Center, told me.
Bennu has been mostly undisturbed for billions of years, so Bennu could be made of material containing molecules that were present when life first formed on Earth, says NASA.
Even so, the actual sampling will be much more difficult than initially planned. That’s because the spacecraft was designed to operate within mostly smooth surface parameters. Since arriving at Bennu some two years ago, however, NASA now realizes that the surface is strewn with boulders and large rocks that will complicate matters.
OSIRIS-REx was designed to be navigated within an area on Bennu of nearly 2,000 square yards, roughly the size of a parking lot with 100 spaces, says NASA. Now, it must maneuver to a safe spot on Bennu’s rocky surface within a constraint of less than 100 square yards, an area of about five parking spaces, noted the space agency.
As for what type sample is best?
“Something surprising,” said Dworkin. I hope for a sample rich in complex organic compounds that tell stories about how life could have formed on the early Earth, or elsewhere in the Solar System, he said.
During a rehearsal for Tuesday’s sampling effort, the spacecraft reached an altitude of some 131 feet — the closest the spacecraft has ever been to Bennu — and then performed a back-away burn, reported the University of Arizona. Nightingale, the spacecraft’s primary sample collection site, is located within a crater in Bennu’s northern hemisphere, said the university.
Around 5:00 p.m. EDT on Tuesday, the spacecraft will begin an hour-long slow descent from its current orbit of some 5500 feet on down to the surface. Its actual contact with this ancient body will last less than five seconds.
Using an ingenious method of sample collection, the spacecraft’s TAG will use an articulated positioning arm that will extend a few feet from the spacecraft. The arm will then release a jet of pressurized nitrogen gas to agitate the surface, enabling the collection of material into the sampler’s holding chamber.
The spacecraft will be on an autonomous program once it begins its descent but its sensors will be able to detect if it’s about to run into trouble with surface hazards. If so, the spacecraft will automatically back off until it reaches an altitude of 16 feet and try again.
The good news is that regardless of what happens Tuesday, Dworkin said that OSIRIS-REx has already demonstrated how to maneuver around a tiny object, and its navigation methods can be applied to other tiny objects like comets and asteroids.
If all goes as planned?
We will begin cataloging and analyzing the sample immediately after its return on September 24, 2023, said Dworkin.
* This article, science journalist and author Bruce Dorminey, was first published in Forbes magazine.