Many spacecraft near Earth rely on signals from navigation satellite constellations like GPS.
These Global Navigation Satellite Systems (GNSS) are each operated by different providers — the U.S., EU, Russia, China, Japan, and India — and have unique designs and characteristics. The absence of required documentation for high-altitude spacecraft has made it challenging for navigation engineers and project managers hoping to take advantage of multiple GNSS constellations, which can enhance navigation accuracy and signal availability.

This week, in a major step towards interoperability, the U.N.-sponsored International Committee on GNSS (ICG) published a new edition of their publication, The Interoperable Global Navigation Satellite Systems Space Service Volume. The ICG was founded in 2005 to facilitate compatibility, interoperability, and transparency between GNSS providers. The new version does exactly that, outlining the specifications of the various GNSS with unprecedented detail.

NASA engineers played a critical role in this milestone, providing technical expertise, encouraging international cooperation, and leading development of this edition of the publication. The document contains the most up-to-date constellation specifications and descriptions of actual performance for missions on orbit. It also contains expanded analysis of performance, like the geometrical distribution of the signals, which is specifically useful for certain space users.

“This is a top to bottom review of the original edition,” said Joel Parker, who leads the GNSS interoperability team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s a thorough update with significantly expanded content.”

This data will help navigation engineers develop systems that can use multiple constellations at once. These multi-GNSS capabilities will increase signal availability for high-altitude space users, allowing them to navigate more accurately and deeper into space.

While a single GNSS constellation can provide reliable signals to spacecraft closer to Earth, spacecraft above these constellations rely on weaker signals from the opposite side of the globe. While NASA has navigated halfway to the Moon using only GPS, missions navigating at lunar distances will profoundly benefit from multiple systems working together.

Soon, NASA and the Italian Space Agency will demonstrate multi-GNSS on the lunar surface, showcasing this capability so that future missions might embrace it. The Lunar GNSS Receiver Experiment (LuGRE) will achieve the first GNSS location fix on the lunar surface using both the U.S. GPS and European Galileo constellations. The experiment will fly on a Commercial Lunar Payload Services mission awarded to Firefly Aerospace of Cedar Park, Texas in 2023.

Key players on the NASA technical team instrumental to the publication of this booklet include J.J. Miller, Joel Parker, Dr. Ben Ashman, Frank Bauer, Mick Koch, Dr. Scott Sands, and Lauren Schlenker. In addition, NASA graphic designer Reese Patillo provided the cover image.

The companion four-minute video, The Multi-GNSS Space Service Volume: Earth’s Next Navigation Utility, explains in clear, non-technical terms the concepts of the Space Service Volume: why it was created, its benefits, and the organizations working to make it a reality. The video was sponsored by NASA and the Space-Based Positioning Navigation & Timing National Coordination Office.