UPDATED: NASA spacecraft makes contact with Bennu in first attempt to sample an asteroid
By Cat Hofacker|October 19, 2020
Maneuver was livestreamed Tuesday
UPDATE: Lockheed Martin and NASA flight controllers received confirmation at 4:12 p.m. Mountain time Tuesday that OSIRIS-REx made contact with the surface of Bennu. Over the next 10 days, scientists will analyze data and images from the touch down to determine if a sample was collected. “Everything we’ve seen from these initial images indicates sampling success,” principal investigator Dante Lauretta said during a post-sampling news conference on Wednesday.
NASA’s yearslong quest to collect its first sample from an asteroid will culminate in a 10-second attempt on Tuesday, in which a circular sampling head will make contact with the asteroid Bennu and attempt to suck an estimated 60 grams of dirt and rocks for return to Earth.
The van-sized Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer has been orbiting Bennu since late 2018, its cameras and science instruments snapping pictures and making detailed maps of its surface and likely composition in preparation for the sample collection.
Scientists hope that when the sample plows through Earth’s atmosphere in its protective capsule in 2023, the mission will yield carbon-rich remnants of the early solar system that scientists can study for decades, as has been the case with lunar samples.
So far, the mission has been rich in surprises. “It’s pretty much giving us every challenge we could have ever imagined and ones we could have never imagined,” OSIRIS-REx project manager Richard Burns told me from his office at NASA’s Goddard Space Flight Center in Maryland, which is overseeing the mission.
The first fine-resolution photos of Bennu’s surface from OSIRIS-REx two years ago revealed a rough surface littered with craggy rocks and deep craters, rather than the relatively smooth surface that engineers and scientists were expecting. They decided to narrow the sample target from a 50-meter-wide swath anywhere on the surface to a sandy, 8-meter-wide patch in Bennu’s north polar region, nicknamed Nightingale. Avoiding obstacles near this two-parking-space-wide spot, in particular a large boulder now dubbed Mount Doom, required NASA and Lockheed Martin to create and upload new software, the Natural Feature Tracking tool. OSIRIS-REx will consult this catalog of photos and models as it autonomously navigates toward the surface. Because Bennu is roughly 330 million kilometers from Earth, a signal would take 18.5 minutes to reach Bennu, so there is no choice but for the collection attempt to unfold without real-time guidance from the ground.
The coronavirus pandemic added another wrinkle, requiring most of the engineering and science team to tune in from their home computers while a limited number of masked and socially distanced flight controllers will be on hand in Lockheed Martin’s control room in Colorado to monitor the spacecraft. NASA is broadcasting the last 90 minutes of the sample collection attempt, called “touch-and-go” or TAG for short, on its website, with coverage starting at 3 p.m. Mountain time. Here’s the sequence of events for the 4.5-hour event:
OSIRIS-REx will fire its thrusters to leave its 900-meter orbit around Bennu, unfolding its robotic arm to point the circular sampling head toward the surface. During this descent, the on-board flight computer will compare the catalog of photos in NFT to those snapped in real time by its navigation camera, NavCam2. If there’s a disparity between the two sources, the flight computer will adjust the trajectory. At 5 meters from the surface, OSIRIS-REx will halt for a final consultation of the NFT software and the on-board hazard map. If the software predicts the spacecraft is on course to contact a smooth part of Bennu, OSIRIS-REx will proceed. If all goes as planned, flight controllers will receive confirmation that the spacecraft touched Bennu’s surface at 4:12 p.m. local time.
The sampling head will touch Bennu’s surface for about 10 seconds, releasing a burst of nitrogen gas through its outer ring that will stir up the regolith, sending the fine grain material swirling into the sampler. Then OSIRIS-REx will fire its thrusters to back away from the surface. Scientists back in mission control in Colorado will receive the first images of the sample collection on Wednesday, and plan to spend the next week examining footage from the sampling camera, SamCam, to determine if OSIRIS-REx collected the required 60 grams of regolith.
If the spacecraft collects less than that amount or aborts the collection attempt to avoid Mount Doom or another hazard, the OSIRIS-REx team will face a difficult choice. The probe could be dispatched Earthward with less regolith, or the team could command it to try to sample another part of Bennu. The sampling head has enough nitrogen gas for three collection attempts, but OSIRIS-REx principal investigator Dante Lauretta has said there’s a chance that in firing its thrusters to back away from Nightingale, the spacecraft will disturb the regolith too much for another attempt there. Instead, ORISIS-REx would return to a 1-kilometer orbit until January, when it would descend toward the backup sampling site, Osprey, located in the center of a 10-meter crater near Bennu’s equator.
In such a choice, scientists and engineers would have to weigh the benefits of collecting all 60 grams of regolith against the possibility of complicating future analysis of the samples by mixing dirt and rocks from the two distinct locations. NASA associate administrator for science Thomas Zurbuchen said that decision will be made by Oct. 30.
“By far, the most likely outcome we will have on Oct. 20 is we will contact the surface and come away with a large sample that exceeds our requirements,” Lauretta told reporters during a pre-sampling briefing, and OSIRIS-REx will depart Bennu in March, beginning the two-year journey back to Earth. As it passes Earth, the spacecraft will eject the capsule containing the sample for a controlled descent under parachutes at the Utah Test and Training Range.
That day will be “Christmas in September,” Lauretta said. “The best Christmas present I’ve ever had.”
Editor’s note: An earlier version of this story incorrectly stated the distance to the asteroid Bennu. The story has been updated with the correct figure.
Related TopicsSpace Science
“It’s pretty much giving us every challenge we could have ever imagined and ones we could have never imagined.”OSIRIS-REx project manager Richard Burns