Flight Testing GPS-Galileo Interoperability for Positioning, Navigation, and Timing Applications

The Global Navigation Satellite System refers to positioning, navigation, and timing satellite constellations operated by the U.S. (i.e., the Global Positioning System or GPS) as well as the European Union and other countries. While GNSS signals from Earth orbiters have successfully calculated positions, velocities, and time up to approximately halfway to the lunar surface, researchers needed further testing to determine if GPS and ESA’s Galileo GNSS could work together to reach the Moon.

A key goal of the flight test was to demonstrate the interoperability of these receivers for computing accurate and safe real-time positioning using GPS/Galileo L1/E1 L5/E5a signals in the highly dynamic environment typical of a launch vehicle.

To test this theory and validate the interoperability of the U.S.’s GPS and the ESA’s Galileo, a Multi-GNSS payload flew aboard the UP Aerospace SpaceLoft sounding rocket. The payload used both satellite navigation systems and two receivers to determine precise location, velocity, and time. Those included:

—A next-generation version of ASI’s Qascom GARSpace GNSS receiver, which was developed to operate in a very highly dynamic environment, went to the Moon on Firefly’s Blue Ghost Mission 1 as LuGRE (Lunar GNSS Receiver Experiment) and became the first technology demonstration to acquire and track Earth-based navigation signals on the Moon’s surface. 

—The ESA’s Fraunhofer GOOSE GNSS Receiver sought to understand the system, its limitations, and operability for future development as well as to inform the upcoming ESA Lunar Pathfinder mission.

“The use of additional GNSS signals to augment GPS is developing rapidly and is a cornerstone of strengthening international collaboration,” said J.J. Miller, principal investigator for the multi-GNSS payload.

The main goal of the suborbital flight test was to assess GPS-Galileo performance in a very highly dynamic environment. A secondary objective was to determine the possibility of augmenting systems such as Autonomous Flight Termination System to utilize Galileo signals along with the native GPS signals for future range safety operations.

During the flight, the GNSS receivers tracked successfully, and with high accuracy, validating that GPS and Galileo signals can be used for lunar/cislunar positioning, navigation, and timing all the way to the Moon. All dual constellation (GPS and Galileo) and dual frequency (L1/E1 and L5/E5a) compatibility and interoperability payload objectives were met.