Four years after leaving Earth, a pogo stick developed in Littleton will touch the surface of the asteroid Bennu, use a vacuum cleaner in reverse to blow up asteroid dirt and catch anything that falls into its ring-shaped container, and then hop back up to the spacecraft that’s been orbiting the asteroid for the past two years.
Of course, it’s not an actual pogo stick nor a vacuum cleaner. But the examples used by NASA and local Lockheed Martin Space Systems engineers help the rest of us picture what is supposed to happen Tuesday around 4 p.m., when the OSIRIS-REx spacecraft briefly touches Bennu to collect samples of objects that could offer insight into our planetary system’s origins.
“The ‘O’ in the OSIRIS-REx mission stands for origins and that’s because one of the prime goals of the mission is to understand the origins of the solar system and that includes the origin of life on Earth,” Jamie Elsila, a research scientist at NASA Goddard Space Flight Center, said Monday during a media call on asteroid science and planetary defense.
OSIRIS-REx launched from Cape Canaveral, Florida, on Sept. 8, 2016, and took two years to travel 200 million miles from earth, though 509 million miles total to reach Bennu, according to Lockheed Martin. Using small rocket thrusters, the spacecraft matched Bennu’s velocity and rendezvoused on Dec. 3, 2018. Since then, scientists have used photos taken by high-resolution cameras built by the University of Arizona to figure out the best spot to land since the surface wasn’t what they originally expected.
Lockheed Martin is taking the lead Tuesday because both the OSIRIS-REx craft and the pogo stick — really, a robotic arm called a TAGSAM, short for touch-and-go sample acquisition mechanism — were developed at the company’s Waterton Canyon campus in Littleton. The campus has commanded and monitored the mission since it left Earth so that’s where mission control will be on Tuesday, though due the coronavirus pandemic, on-site access is limited. It’ll be much easier to tune into NASA TV starting around 3 p.m. to view the event.
The carefully planned mission expects to touch the asteroid during a live broadcast at 4:12 p.m. in Colorado — or 18.5 minutes after touchdown occurs because it takes that long for data to travel back to Earth. The adventure has not always gone as expected, said Sandra Freund, lead engineer and Lockheed Martin’s OSIRIS-REx Mission Operations Manager.
“The science team has some good ideas about what they think will happen, but that has been one of the biggest surprises of this mission,” Freund said. “We designed the spacecraft and our sample collector (for) what we thought was going to be a beach. And as they got closer to Bennu and started taking those more high resolution images we realized that the surface is very rocky.”
The rocky surface became an issue because TAGSAM was designed to collect tiny things — material of up to 2 centimeters in diameter or objects slightly smaller than a nickel. There’s no room for Bennu’s boulders. The team began hunting for a hospitable spot and in December picked the Nightingale crater because it appeared to have that fine-grain material like beach sand.
After a dress rehearsal in August, which didn’t touch the crater but got about 40 meters away, the spacecraft will begin descending to Bennu’s surface around 11:15 a.m. on Tuesday for its 4.5-hour sample collection journey.
There are nearly 1 million known asteroids out there. So, why Bennu?
Heather Enos, OSIRIS-REx deputy principal investigator who’s part of the University of Arizona, Tucson science team working with Lockheed and NASA, offered three good reasons: its proximity to Earth, its smaller size and its evidence of carbon-rich and water-bearing material needed for life.
“We wanted pristine carbon-rich asteroids that would unlock clues to the formation of the solar system, unlike Earth and life as we know it today,” she said. “And we do have good ground-based evidence that Bennu is a carbon-rich asteroid. So it became our choice for sample collection (Tuesday).”
But this isn’t a mission to find life — the asteroid is too small and the radiation (in space) would kill anything, Elsila said.
“But we’re looking for those building block molecules because those are going to help us understand what the ingredients were in the early solar system when life arose on Earth and how those organic molecules might have been delivered to the Earth’s surface and maybe to elsewhere in the solar system as well,” Elsila added.
NASA also is working on two other asteroid-related missions, Lucy and Psyche. Lucy is expected to launch in 2021 to study Jupiter’s Trojan asteroids, while Psyche launches in 2023 to study Psyche, a giant metal asteroid in the main asteroid belt.
NASA is also working with space agencies in Japan and Canada to share data on asteroids. Japan’s Hayabusa2 became the first to collect surface and subsurface material from the asteroid Ryugu last year. This will be NASA’s first time to collect asteroid dirt and the two missions plan to share samples.
Some of the asteroid research is partly to also track where asteroids are and what to do if one starts heading in our direction. “We want to have a demonstrated mitigation capability,” said Andrea Riley, NASA’s mission program executive for DART, the Double Asteroid Redirection Test.
But for the most part, the research is to help us understand where our solar system came from, said Hal Levison, the Lucy mission principal investigator at the Southwest Research Institute in Boulder.
“The small body populations are really our best chance of trying to figure all this out,” said Levison. “When I got into this a long time ago, we used to believe the planets sort of formed in the region we now see them. And really what happened is that it’s as if somebody picked up the solar system and shook it real hard. And so these objects that are left over have moved a lot and have witnessed a lot. And in order to really put the whole story together, it requires a big sample set.”
How TAGSAM works
Due to low gravity, OSIRIS-REx can’t land on Bennu. That’s why TAGSAM is more like a pogo stick that will hit the surface for 5 to 15 seconds and then lift back up to the spacecraft.
During those precious seconds, the TAGSAM will fire a bottle of compressed nitrogen gas on Bennu’s surface to stir up the regolith, or dirt, like a reverse vacuum cleaner. The disrupted materials are expected to lift upward so the TAGSAM’s ring-shaped container, which looks like an older car’s air filter, can collect the samples and bring them back to the spacecraft.
The device was developed by Jim Harris, a Lockheed engineer who worked in Littleton and has since retired, Freund said.
“He was in a gravel driveway with an air compressor and a cup and just wondering, ‘Could I do this?’ And so that’s kind of where the idea was born,” she said. “And then when it came time for the next set of missions they said, ‘Hey, we could use this to collect material from a surface.’ OSIRIS-REx mission was that mission.”
Colorado has a large aerospace industry, with more than 1,000 companies and 27,600 employees as of 2019, according to the state’s Economic Development and International Trade office. It’s also home to United Launch Alliance, which sent OSIRIS-REx into space back in 2016.
“We’re excited about how this will open the doors and minds of a lot of young people, ‘You mean I can go out there and touch something?,’” said Rich Cooper, vice president for the Space Foundation, which provides industry and educational events and operates the Discovery Center in Colorado Springs. “This is another example of Lockheed’s incredible leadership in the space community.”
The Space Foundation is also hosting OSIRIS-REx watch parties on its Facebook page on Tuesday.
The OSIRIS-REx team won’t know until Wednesday, at the earliest, whether the TAGSAM collected anything. But it’ll have two more bottles of compressed nitrogen to give it another go before it leaves for Earth next March.
The perfect sample?
“The best outcome would be that we would collect a massive sample,” said Enos, with the University of Arizona that will study the samples when it returns to Earth in 2023. “…I would love for the container to be completely full.”
The TAGSAM needs to collect 60 grams, or 2 ounces, of material but the container has room for 2,000 grams, or about 4.4 pounds.
“Obviously we want something that represents the new signatures of carbon rich and hydrated minerals, so that would be amazing and I have every reason to believe that that’s going to be in that sample,” Enos said. “I would love tiny grains. I would like a couple at almost the maximum of two centimeters that we can ingest. Diversity is the key to being able to get the most out of that sample.”
The samples will be transported to Utah after the mission returns to Earth in September 2023. They’ll then stop by the Johnson Space Center and later be turned over to a team at the University of Arizona to study how the solar system was formed, said Freund.
“They don’t believe we have anything like this material on Earth today,” Freund said of the researchers. “And so they’re super excited just to have these in the lab to be able to better understand the composition of Bennu and help them fill in some of the pieces of how the solar system was formed.”
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