SAN FRANCISCO – A NASA formation flight experiment shows the promise of autonomous navigation for swarms of satellites.
The four cubesats in the Starling Optical Formation Flight Experiment, or StarFOX, calculate their orbits by combining visual images from star trackers with robotic algorithms.
“Such a visual navigation system on a swarm of satellites can be used to navigate around the Earth,” Simone D'Amico, associate professor of aeronautics and astronautics at Stanford University and founding director of the Stanford Space Rendezvous Laboratory, told the BBC. Space News“Since we don’t use GPS, it can be used to fly around the Moon or Mars with a higher level of autonomy.”
Mission operators communicate with Starlinga swarm of four cubesats launched on a Rocket Lab Electron rocket in July 2023, as a single entity. StarFOX is one of four experiments testing communications, navigation and autonomy technologies for future swarms.
Overall, Starling has proven promising enough for NASA to extend the mission. Starling, which was originally scheduled to conclude in May, has been extended until December 2025.
Combined algorithm
Previous flight tests of vision-based navigation used an observer satellite and a target, with the observer knowing the initial location of the target.
StarFOX has demonstrated that it is possible for four satellites to navigate autonomously “without prior information and without maneuvers to improve navigation accuracy,” D'Amico said.
The key to StarFOX's success is a set of algorithms called Angle-Only Absolute and Relative Trajectory Measurement System (ARTMS), according to A paper Presented at the recent Small Satellite Conference in Logan, Utah, ARTMS combines algorithms for image processing and initial orbit determination with an algorithm that refines estimates of the swarm state over time.
“We’ve learned what accuracy can be achieved using typical star trackers used on small satellites,” D’Amico said. “And we’ve learned how we can improve that performance, for example by sharing these visual measurements taken by multiple observers.”
Starling satellites exchange data via inter-satellite links.
“If multiple observers see a common target in the field of view, sharing these measurements and incorporating them into our algorithms can more accurately and quickly determine the orbit of that object,” D’Amico explained. Sharing data also improves each satellite’s understanding of its own orbit, he added.
Required tests
StarFOX also demonstrated the importance of rigorous testing.
“We learned the importance of performing full hardware testing on the ground loop prior to flight,” D’Amico said. “In order to meet budget and time constraints, we performed individual unit tests and sacrificed some of the integrated tests that would have given us full confidence in running the experiments.”
Early in the Starling mission, the flight software crashed. Using a ground-based engineering model, a software engineer at NASA Ames Research Center worked around the problem by allocating additional memory.
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