The NASA spacecraft orbiting an ancient asteroid more than 52 million miles from Earth is doing really well navigating its target. In fact, it is doing so well, its navigation team knows down to a meter where OSIRIS-REx is heading. That's better than what your smartphone can do for you on Earth.
OSIRIS-REx launched from Kennedy Space Center in 2016 and caught up to the 4.5 billion-year-old asteroid named Bennu late last year. Since its arrival, mission scientists have already learned a lot about Bennu, which was selected because it contained water and other life-supporting chemical compounds. The spacecraft will collect a sample from Bennu next year and return it to Earth in 2022.
On Tuesday, members of the mission team detailed some findings OSIRIS-REx made and mission successes in the first three months at Bennu.
Originally, the team was looking for a 82-foot radius area with few boulders or hazards, to allow OSIRIS-REx to collect a sample from, but they now know that type of area doesn’t exist on Bennu. The asteroid is more rugged and rocky than they had estimated.
But the spacecraft's navigation is up for the challenge.
"We feel confident that our teams and our systems are up to the task to collecting from a much smaller area," said Rich Burns, OSIRIS-REx project manager, with NASA’s Goddard Space Flight Center.
When OSIRIS-REx first began orbiting the asteroid, it transitioned from navigating by the star in the background of Bennu to using landmarks on the asteroid’s surface. It's the smallest object ever orbited by a spacecraft, according to NASA.
Coralie Adam, an OSIRIS-REx flight navigator with KinetX, said the spacecraft has demonstrated navigation down to the meter -- "better than your smartphone" -- orbiting less than a mile from the surface.
"The navigation performance has been exquisite," Burns said, adding that this will make the sample collection by the spacecraft's arm -- theTouch-And-Go Sample Acquisition Mechanism --, known as TAGSAM, go flawlessly.
"Like throwing a dart at the board, we’re going to try and hit the center of the bulls’-eye," Burns said.
Bennu also threw a literal curveball at the science team.
Mission principal investigator Dante Lauretta, with the University of Arizona, said images from the spacecraft show Bennu is frequently ejecting particles from its surface.
"We have certainly never seen anything like this from a spacecraft before," Lauretta said, mentioning other asteroid spacecraft, including Japan's Hayabusa missions. "None of those mission have ever seen particle ejection."
Some of the material spewed out leaves the asteroid completely while other particles remain, creating satellites of Bennu.
University of Central Florida physics professor Humberto Campins said that means Bennu is an active asteroid, not an inert body.
Active asteroids can show activity similar to that of a comet, including dust, and sometimes be designated as a comet and an asteroid. Out of 800 million asteroids larger than 1 kilometer, only about a dozen have been found to be active, Campins said.
Campins is on the spacecraft's imaging team, helping to search for the best site for a sample collection. He said the new discoveries about Bennu are making the sample site search more challenging.
"We know so little about these. We need to do a lot more studying," Campins said. "We need to know if they are from the same areas or different and how much energy is behind it."
As OSIRIS-REx approached Bennu, Campins said, the imaging team was looking for dust or natural satellites around the asteroid that would indicate it was active but, at first, didn't find anything. In January, as the team prepared to shift from navigating the spacecraft by the stars to navigating by the asteroid's surface features, they saw something weird going on.
"When we went into orbit, they started to see more stars," Campins said, adding that the team quickly realized, "Oh, these are not stars." It was debris from Bennu's particle-throwing activity. Since the first sighting, 10 other such ejections from Bennu were spotted in two months, he said.
To understand the driving forces behind this action, the spacecraft's navigation team members are tracking the ejected material image by image, following the path of the particles, Adam said.
"Bennu is really teasing us with this," Lauretta said. "Every time we think we know what's going on, we go back to the drawing board."
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