NASA Tests GPS-Free Navigation System Using Spacecraft and Debris

NASA has tested a navigation system that allows satellites to determine their position without relying on GPS. Instead of depending on an external navigation network, the system uses other spacecraft and orbital debris as reference points to work out where a satellite is in space.

The technology, called FALCON, was tested as part of NASA’s Starling mission. FALCON stands for Fast Autonomous Lost-in-space Catalog-based Optical Navigation. According to Science Daily, during the demonstration, the system not only helped a spacecraft determine its own orbit but also improved the estimated orbits of more than 200 other space objects in just three days.

The test is aimed at making spacecraft more independent. GPS signals that satellites use near Earth can become weak, unreliable or unavailable around the Moon and in deep space. A system that allows spacecraft to navigate using objects they can observe could therefore support missions that cannot depend on GPS. The FALCON experiment used Starling’s onboard cameras and a catalogue of known satellites and other space objects. The cameras, which are also used for tracking stars, observed objects around the spacecraft. FALCON then compared those observations with information in a publicly available catalogue of known space objects maintained by the US Department of War.

How FALCON uses space objects as landmarks

FALCON uses objects already present in orbit as reference points. These can include other spacecraft and pieces of orbital debris. Once the system identifies and verifies the objects seen by Starling’s cameras, it can use their known positions to calculate Starling’s own orbit. This means the spacecraft does not have to depend entirely on navigation information sent from outside. Instead, it can use what its cameras observe around it to help determine where it is.

The system was also tested for another task: improving information about the objects it observes. Mission controllers loaded a catalogue containing about 20,000 space objects and their predicted orbits onto Starling. FALCON then compared the predicted information in that catalogue with measurements collected by Starling’s cameras. From those measurements, it calculated Starling’s position while also refining the estimated locations of other objects.

The results showed that the updated estimates could be more precise than the existing catalogue information. Over three days, FALCON improved the known orbits of more than 200 objects without requiring intervention from operators on the ground.

First demonstration of its kind

NASA said FALCON’s ability to determine a spacecraft’s own orbit using optical cameras and its position relative to other objects represents a first for this type of spacecraft navigation. The experiment also showed that Starling could produce improved predictions of where observed objects would be compared with information supplied by ground stations. This could be useful for missions in which spacecraft need to operate with less dependence on Earth-based systems.

“FALCON is yet another success for the Starling demonstration mission. The results from FALCON can have far-reaching implications for on-orbit space-traffic monitoring, collision avoidance, and alternative navigation,” said Roger Hunter, programme manager for NASA’s Small Spacecraft and Distributed Systems programme at NASA’s Ames Research Center in California’s Silicon Valley.

The ability to navigate independently could become important as NASA works on missions farther from Earth. The agency said the technology could support lunar satellite swarms, distributed science missions and future human exploration. Precise positioning is particularly important for distributed science missions. In these missions, several spacecraft can collect measurements from different locations, making accurate knowledge of their positions necessary to align and use those measurements properly.

Autonomous navigation could also have a role in space-traffic management. If spacecraft can determine their positions and update information about objects around them, they could reduce some dependence on ground-based tracking networks while supporting collision avoidance.

From University research to space test

FALCON was developed through a joint flight experiment between NASA and EraDrive, a startup that emerged from Stanford University. The system combines EraDrive’s Era-Core flight software and embedded algorithms with Starling’s cameras and its onboard catalogue of known satellites. The work originally began as a University SmallSat Technology Partnerships project. It later developed into EraDrive, which is commercialising its Era-Core software and related hardware for wider use.

Starling provided an opportunity to test the technology in actual space conditions. The demonstration showed how flight software and onboard observations can be combined to give spacecraft greater autonomy. The testing is not finished yet. Later this year, Starling is expected to expand the FALCON experiment using Era-Core. The mission’s four spacecraft will share tracking information with one another and use the combined observations to refine their positions collectively.

NASA’s Ames Research Center leads the Starling mission. NASA’s Small Spacecraft and Distributed Systems programme, based at Ames and part of the Research and Technology Mission Directorate, funds and manages the mission.