Space

NASA to improve Global Navigation Satellite System (GNSS) efficiency for more accurate and reliable positioning and timing data

Summary

NASA is advancing its capacity to see an increased use of signals from the Global Navigation Satellite System (GNSS) constellation. These signals could provide more accurate and reliable positioning and timing data to the Artemis missions to the lunar Space. […]

NASA is advancing its capacity to see an increased use of signals from the Global Navigation Satellite System (GNSS) constellation. These signals could provide more accurate and reliable positioning and timing data to the Artemis missions to the lunar Space. GNSS signals are used on earth for navigation and critical timing applications. GNSS is similar to GPS. However, the two differ in certain aspects. GPS cannot use navigational satellites from other satellites but the GPS- specific ones. However, for GNSS, this is not the case. Equipment compatible with GNSS can use navigational satellites from other networks. This makes data from GNSS more accurate and reliable. NASA’s space communications and navigation (SCaN) program is advancing robotics, which will reinforce this ambition.

With six GNSS constellations providing Position, Navigation, and Timing (PNT) services, coordination of the GNSS satellites is crucial. Four of these constellations serve on a global scale, while the other two offer regional coverage. Global players in GNSS include those operated by the US, Russia, the EU, and China. Indian and Japanese constellations are regional. The upside to using multiple constellations at once is that it gives more signal availability. The more the signal, the more the accuracy of the timing and navigation for satellites. Spacecrafts at higher altitudes could benefit from multiple constellations because the higher the altitude, the lesser the signals. With most constellations having unique blueprints, engineers will face serious challenges in developing multi-GNSS systems that adopt multiple constellations.

An example of NASA’s creations in support of this goal is the Bobcat-1. It is a small satellite, selected by Cubesat Launch Initiative in 2018.Bobcat-1 was launched to the ISS on October 2, 2020. It was developed by a partnership between NASA and Ohio University Avionics Engineering Center. The Bobcat-1 mission is to study GNSS, focusing on improving the availability and performance of PNT services for other satellites and spacecraft.

Bobcat will orbit for nine months, checking signals from various GNSS constellations. Engineers will use this data to find out how GNSS performs across the different constellations in timekeeping. “GNSS users at high altitudes see fewer satellites. Time offsets between the constellations can be measured by the Cubesat and provided to these users to improve their positioning performance,” said Frank van Grass, Bobcat’s co-principal investigator.

SCaN Testbed laid a foundation for Bobcat-1 by manifesting Multi-GNSS abilities On the ISS. The Testbed was operated from 2012 to 2019, paving the way for Bobcat-1 to be launched in 2020. The Testbed receiver, also known as the GPS and Galileo Receiver for the International Space Station (GARISS), received signals from both GPS and EU’s Galileo. GARISS was developed through a NASA-European Space Agency (ESA) partnership.

The Testbed’s legacy also spearheaded the lunar GNSS Receiver Experiment (LuGRE). It is a payload on the works, aimed at receiving signals from both GPS and Galileo. The payload will help to put GNSS on the surface of the moon. It is an alliance between NASA and The Italian Space Agency. “GNSS capabilities continue to revolutionize the ways spacecraft navigate in near-earth Space and beyond. NASA’s outstanding relationships with the GNSS providers have advanced these capabilities to new heights and support the Artemis Mission on and around the moon,” said Joel Parker, NASA’s navigation engineer.