NASA’s spacecraft is set to descend on asteroid Bennu on Oct. 20. We spoke with the project scientist about the challenges of robotically sampling a space rock millions of miles away.
In the coming days, OSIRIS-REx is set to robotically scoop an asteroid sample more than 200 million miles from Earth. On Oct. 20, the OSIRIS-REx spacecraft will descend on asteroid Bennu to collect a sample of its surface in what NASA has officially dubbed a Touch-And-Go (TAG). If successful, the cosmic bounty could be the space agency’s largest space sample recovery since the Apollo era, according to NASA. We recently spoke with Jason Dworkin, the project scientist for OSIRIS-REx, about the upcoming TAG, the “greedy” tendencies of asteroid sampling, and more.
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OSIRIS-REx: Contamination risks and mission challenges
Prior to providing sample analysis on the OSIRIS-REx mission, Dworkin collaborated on the Curiosity mission, provided analysis on the Stardust mission, and is the current international deputy for the soluble organics team for the JAXA Hayabusa 2 mission.
“My science role in the mission is sample analysis. So the vast majority of my science hasn’t started yet. I’m still waiting for that. And that will happen in 2023 when the sample comes back, but [I’ve] also been heavily involved in, or actually helped design the contamination, knowledge, and contamination control plan of the mission to make sure the samples [that] come back are pristine,” Dworkin said.
Sending a spacecraft millions of miles into the cosmic vacuum to scoop a hunk of space rock is a herculean task in and of itself, however, eliminating the risk of cross-contamination to ensure the scientific integrity of said sample comes with no shortage of challenges. These contamination efforts were central to the mission’s planning, construction, journey to Bennu, and beyond.
From the start, the team set amino acid requirements for the spacecraft and used these proteins as a proxy for potential biological contamination such as bacteria, fingerprints, and more, according to Dworkin.
Remember, something as minuscule as a stray microscopic nylon fiber could contaminate the craft or sample.
“When nylon degrades, it turns into amino acids and that would break our requirements and nylon-6 in fact breaks down to ε-amino-n-caproic acid, don’t worry about the name, but that’s seen in some meteorites [and] therefore might be of interest for Bennu,” Dworkin said.
As a result, the team went to great lengths to ensure nylon elements were not introduced to the craft’s environment during construction and prep for launch, including media opportunities.
“Some of the clean garments are nylon so we had to get rid of all of those and make sure that none got in. No nylon zip ties, only the Teflon zip ties. No nylon [bags or] nylon zippers,” Dworkin said.
“We had the camera crew [come in and] we had to take off the nylon straps on the camera gear and then clean everything, so lots of really annoying details that we had to focus on and I’m looking forward to seeing it pay off,” Dworkin continued.
Bennu survey, sample collection, and mission surprises
Pinpointing a specific sample site on an object slightly wider than the Empire State building is tall is a big ask to say the least. Although OSIRIS-REx first reached Bennu in 2018, scientists have been studying the asteroid for decades, Dworkin explained. During this time NASA has gained invaluable insights about Bennu’s potential makeup with a few surprises along the way.
Using telescopes to monitor how quickly the asteroid heats and then cools as it rotates it’s possible to make predictions about Bennu’s surface, Dworkin said, using a sand and asphalt juxtaposition to explain the method. While sand heats and cools quickly, asphalt, on the other hand, heats and cools comparatively more slowly.
Based on the thermal inertia data collected, the team had made certain predictions about Bennu’s surface.
“We thought that the entire surface of Bennu would be like a flat sandy beach or gravelly beach, except for one rock we detected from the radar measurements. That turned out to be totally wrong. The asteroid is a rocky, rough place,” Dworkin said.
From more than one mile away, the craft would then spend months surveying and mapping the asteroid in “unprecedented” detail. In 2019, the team selected the Nightingale site for sample collection. Situated in Bennu’s northern hemisphere, NASA believes the area to be “relatively young, and the regolith is freshly exposed” allowing the craft to collect “a pristine sample of the asteroid.”
These detailed maps will also play a key role in the craft’s descent to the surface.
During the attempt, the craft will be more than 200 million miles from Earth. At this distance, there’s about a 18.5-minute communication delay. As a result, the OSIRIS-REx team will uplink commands beforehand. The craft will then perform the entire descent and collection autonomously using a set of onboard maps to navigate.
“Part of the natural feature tracking approach is to generate these maps. So we have detailed maps of the sampling site and the onboard computer has a number of different spots, different natural features for specific rocks that are identified that it can match,” Dworkin said.
The concept is similar to the approach used on the Mars 2020 mission during entry, descent, and landing, although the two locations will present markedly different variables. Whereas the Mars 2020 spacecraft (with Perseverance in tow) will enter the Red Planet’s atmosphere at about 12,000 mph deploying a parachute to slow the craft and prepare for landing, OSIRIS-REx will make its approach at a more gingerly pace.
“That freefall takes 10 minutes because we’re going at 10 centimeters per second. So it’s the opposite of Perseverance, [so] instead of seven minutes of terror it’s 10 minutes of boredom,” Dworkin said.
Once in position, the craft is set to begin its sampling attempt. At this point, it fires one of three pressurized nitrogen canisters to agitate the asteroid’s surface and collect this material in the specially designed collection device. Dworkin provided a little background on this device, explaining the origins story behind a sampling system design contest and Lockheed Martin’s “ingenious plan.”
“One of the engineers went to his driveway with a Solo cup and an air compressor and did a proof of concept there. And he won the prize. And the first name was actually called “Muucav,” which is vacuum backwards because that’s in essence what it is,” Dworkin said.
The “dinner plate-sized” device essentially functions like a “backwards air filter,” Dworkin explained, and once the craft fires the nitrogen, rocks and dust from the surface are captured inside. Exactly how much material is captured will depend on a host of variables.
“We’ve done testing under microgravity in the vacuum and in odd angles and [with] obstructions, and the collection device almost always performs well above requirements. We are requiring 60 grams of sample. However, we frequently get hundreds of grams in our testing and it has [a] capacity of two kilograms,” Dworkin said.
“As a sample scientist, of course, I’m greedy. I want the most, but we can achieve all of our science with the 60 grams,” Dworkin said.
Bennu sample analysis in the years ahead
If successful, this collection attempt could be NASA’s largest sample returned to Earth since the Apollo era, according to NASA. This material will provide researchers with invaluable information related to the formation of the solar system, the origins of life, and more. Dworkin explained that the research team will test 25% of the sample with 75% set aside for future generations of scientists.
“It can be stored for years. Just like Apollo [samples] have been, such that even scientists who are not yet born using techniques not yet invented can answer questions not yet asked,” Dworkin said.
As mentioned previously, OSIRIS-REx has three onboard pressurized nitrogen canisters. If the craft fails to collect a sample on the first attempt, it can attempt two more TAGS. The team has attempted to practice maneuvers ahead of TAG, according to Dworkin, and both of these “were perfect.” While Dworkin admitted that there is a bit of luck involved with a successful attempt, he remains optimistic.
“The spacecraft shouldn’t have any problems. The team is remarkable. The spacecraft has been virtually trouble-free since launch and it’s really well designed, so I don’t think that Bennu will defeat it,” Dworkin said.