To teach an old spacecraft new tricks to explore the moon

NASA’s spacecraft Lunar Reconnaissance Orbiter (LRO) far exceeded its planned mission duration and revealed that the moon contains surprises: ice deposits that can be used to support future lunar exploration, the coldest places in the solar system in permanent shadow regions at the lunar poles. , and that it is an active world that shrinks, generates lunar tremors and changes before our eyes. LRO mapped the surface in fine detail, returned millions of images of a stunningly lunar landscape, and paved the way for future human missions under NASA’s Artemis program.

In the spring of 2018, LRO’s Miniature Inertial Measuring Unit (MIMU), a critical sensor used to help direct the spacecraft’s instruments, was shut down to preserve surviving life after showing signs of deterioration due to natural aging in the harsh environment. The MIMU is like a speedometer. It measures the speed of LRO. Without it, LRO was forced to rely only on data from star trackers – video cameras with image processing software based on star charts – to show and reorient the spacecraft. “This has limited the ability to reorient (kill) the spacecraft for scientific purposes,” said Julie Halverson, chief systems engineer in space science mission operations at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“Reorienting spacecraft scientists to get side-by-side data is valuable for scientists, as it enables us to measure how light reflects off the moon differently, depending on the image of the instrument,” he said. Noah Petro, project scientist for NASA’s NASA Goddard, said. “This is called the photometry of the surface. In addition, the camera takes side-view photographs to build 3D images of the surface and to collect the perspectives of the moon that help disrupt geological relationships.” To get LRO running again, NASA engineers have developed a new algorithm that can estimate the LRO’s rotational speed by merging star tracker measurements, along with other information available on LRO’s flight computer.

In order for the new LRO speedometer to work properly, the stargazers must maintain an unobstructed view of the stars, which can be blocked by the earth or the moon or the glare of the sun. Otherwise, it is impossible to determine the orientation or estimate the rotational speed of the spacecraft. The assurance that the star trackers are always obstructed during scientific maneuvers has made many scientific observations that can be easily made with the MIMU impossible to perform without them. To recapture these otherwise lost opportunities, Goddard, NASA’s Engineering Safety Center (NESC) and the Naval Postgraduate School (NPS) in Monterey, California, have reunited in their long history of collaborative research to quickly develop a collection of new, revolutionary methods. to develop. to enable LRO to fully explore the Moon.

“The algorithm we developed for LRO is called Fast Maneuvering or ‘FastMan’, and it works in collaboration with LRO’s star tracker-based controller,” said Mark Karpenko, a research fellow at NPS and the FastMan Project Lead . “The maneuvers naturally send clear objects, just like avoiding obstacles in a self-driving car.” A computer algorithm is a set of instructions for processing data. Karpenko was able to construct FastMan using software tools based on the same tools previously used by a NASA-NPS team to reorient the International Space Station by combining forces from the spatial environment with its gyroscopes rather than refueling burned by firing his thrust. . This “Zero Propellant Maneuver” is similar to an attacking maneuver used in sailing.

“The Lunar Reconnaissance Orbiter undergoes regular special periods as it orbits the Moon, and our ability to plan these slaves is limited by the time it takes to execute them,” said John Keller, deputy project scientist for LRO at NASA Goddard, said. With FastMan, LRO was able to execute nearly 200 additional sequences that could not otherwise be executed.

“Most of the performance improvements we’ve achieved so far have actually been by using the results of FastMan to create a ‘taxicab’ maneuver,” Karpenko said. Because the full FastMan required changes to LRO’s flight software, Karpenko designed the taxi maneuver to achieve most of FastMan’s objectives, while requiring no modifications to the flight software. “Unfortunately, until we could update the flight software, I had to be on the run,” Karpenko said. The full FastMan maneuver is completely autonomous.

The first FastMan series was launched at the end of July 2020 and enabled the LRO Camera, one of the seven scientific instruments of LRO, to get a side-view of the Triesnecker crater 25 percent faster than what a taxi-taxi would have allowed. With these new algorithms, LRO is again able to look to the side quickly and the spacecraft is healthy, with all instruments still collecting data. “LRO is now in year 11 of what was originally supposed to be a two-year mission,” Petro said. “We monitor all LRO systems regularly for signs of deterioration or change. Fuel could be our rate-limiting factor, according to current estimates we could still have at least five years of fuel on board, if not more.”

In 2010, NPS, NESC and Goddard worked together to implement the first minimum reorientation maneuvers ever performed on a runway. This innovative work was done as a flight demonstration at the end of life on the TRACE spacecraft. Today, the lunar science community is the beneficiary of this groundbreaking work. “The swing algorithms developed by NPS have already enabled LRO to gather more science,” explained Neil Dennehy, NASA Technical Fellow for Guidance, Navigation and Control. “I expect that our industry partners will also be able to utilize this technology in the future.”

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