South SFV Today

Researchers at Stanford University's Space Rendezvous Lab have conducted the first in-orbit test of a prototype system designed to navigate a swarm of satellites using only visual information shared through a wireless network. This test, known as the Starling Formation-Flying Optical Experiment (StarFOX), successfully navigated four small satellites working together by using onboard cameras to calculate their trajectories.

Simone D’Amico, associate professor of aeronautics and astronautics and senior author of the study, remarked, “It’s a milestone paper and the culmination of 11 years of effort by my lab, which was founded with this goal of surpassing the current state of the art and practice in distributed autonomy in space.” He added, “Starling is the first demonstration ever made of an autonomous swarm of satellites.”

The findings from the initial StarFOX test were presented at the Small Satellite Conference in Logan, Utah. NASA has also launched four CubeSats into orbit to evaluate their ability to autonomously cooperate without real-time updates from mission control. This experiment aims to test key technologies for future deep space missions.

D’Amico emphasized that robust navigation for satellite swarms presents significant technological challenges. Current systems rely on terrestrial networks like GNSS or the Deep Space Network beyond Earth’s orbit. However, these systems are slow and not easily scalable for future missions. Additionally, they cannot help satellites avoid "non-cooperative objects" such as space debris.

The team developed a self-contained navigation system that enhances autonomy and robustness using minimal technical requirements and financial costs associated with today’s miniaturized cameras. The cameras used in StarFOX are inexpensive 2D star-trackers found on most satellites.

“At its core, angles-only navigation requires no additional hardware even when used on small and inexpensive spacecraft,” D’Amico stated. “And exchanging visual information between swarm members provides a new distributed optical navigation capability.”

StarFOX combines visual measurements from single cameras mounted on each satellite in a swarm. Similar to historical mariners navigating with sextants, known stars serve as references to extract bearing angles to other swarming satellites. These angles are processed onboard through physics-based force models to estimate positions and velocities relative to Earth or other planetary objects.

The Space Rendezvous Lab's Absolute and Relative Trajectory Measurement System (ARTMS) integrates three new space robotics algorithms: an Image Processing algorithm that detects targets in images; a Batch Orbit Determination algorithm that estimates coarse orbits; and a Sequential Orbit Determination algorithm that refines trajectories over time for autonomous guidance and collision avoidance.

Data is shared via an inter-satellite communication link to calculate accurate absolute and relative positions without GNSS. Under challenging conditions with just one observer satellite, StarFOX achieved relative position accuracy within 0.5% of their distance; multiple observers reduced error rates further to just 0.1%.

NASA has extended the project under StarFOX+ through 2025 based on promising results from this initial test phase.

Additional co-authors include Stanford graduate student Justin Kruger and Soon S. Hwang from NASA Ames Research Center. The research received funding from NASA's Small Spacecraft Technology Program within its Space Technology Mission Directorate along with support from the Air Force Office of Scientific Research.