A miniature CubeSat has become the first satellite to perform Galileo-based position fixes in orbit using a commercial satnav receiver.
CubeSats are nanosatellites based on standardised 10 cm-sized units. Originally devised for educational uses, they are nowadays being put to commercial and technology testing uses. The Swiss Astrocast company is assembling a constellation based on 3-unit CubeSats to serve the emerging ‘Internet of Things’.
Vigilant for new initiatives that foster innovation in the field of navigation, ESA navigation researchers supported Switzerland’s ETH Zurich technical university to fly a navigation payload – composed of four low-cost multi-constellation mass-market satnav receiver modules plus two antennas – aboard a test CubeSat.
“This mission has demonstrated the first use of Galileo to perform positioning and timing in orbit supporting precise orbit determination using a commercial product developed for ground users,” explains ESA’s Global Navigation Satellite Systems (GNSS) R&D Principal Engineer Roberto Prieto Cerdeira.
“The purpose of this initiative was to demonstrate the capabilities of Galileo in orbit with a small, low-cost, low-power European satnav receiver. This will pave the way for future navigation experimentation, scientific experiments and technology demonstrations of Galileo in orbit with CubeSats and low-cost receivers for scientific activities.
“The navigation payload is also capable of performing position fixes by combining Galileo with the US GPS, Russian Glonass and Chinese BeiDou systems for increased performance.”
ESA R&D navigation engineer Rok Dittrich adds: “The receiver itself was not specially developed and tested for space but is a modified version of a low-cost mass-market product from the Swiss u-blox company. It underwent ground testing emulating its use in space, along with firmware added to take into account the dynamics of low-Earth orbit.”
This opportunity, funded through ESA’s European GNSS Evolution programme, was conceived together with ESA’s Galileo Science Advisory Committee, a group of scientists advising ESA on scientific matters related to Galileo and fostering its scientific exploitation.
This first AstroCast CubeSat was launched in December 2018, and the first results confirming the use of Galileo satellites for positioning were reported at the recent Galileo Science Colloquium in Zurich, typically demonstrating orbital positioning precision down to less than 5 m.
ESA’s Galileo Navigation Science Office and GNSS Evolution are looking into extending this pioneering experience to perform more CubeSat-based experiments in space to test ideas for evolutions of European satnav systems and scientific experiments with Galileo, in partnership with universities and research institutions.
Satnav serving space
Satnav is already widely used by satellites in low-Earth orbit for guidance, navigation and control, relying on the satnav constellations flying above them in medium-Earth orbit. Some telecommunication and weather satellites in higher orbit also make use of the satnav signals flying at lower orbit, with very weak satnav signals from satellites located at the other side of the Earth.
For the future, satnav is a key enabling technology for the safe operation of low-Earth orbit constellations, allowing individual satellites to maintain optimum formation relative to the other constellation members.
ESA and NASA have previously demonstrated Galileo-only and Galileo-GPS fixes from the International Space Station, although using a space-qualified software-based receiver.
ESA is developing dual Galileo-GPS receivers for the next generation of Earth-observing Copernicus Sentinel satellites. The more precise the orbit determination, the more accurate the environmental data that can be returned to Earth.
Combined use of Galileo and GPS signals on an interoperable basis for positioning and precise orbit determination should bring significant advantages for space users in particular, set to provide a seamless navigation capability from low to high Earth orbits – and potentially beyond.