Forward(ing) from the moon - lunar pathfinder data relay satellite, paving the way for communication and navigation constellation

Abstract

Lunar Pathfinder is the first commercial data-relay satellite, providing cost-effective, high-performance communication services to the next generation of lunar missions. Since the unveiling of the Lunar Pathfinder vision, progress has been made steadily, and the spacecraft is on track to begin operations as early as 2025. Within the last year, SSTL Lunar have been actively working with ESA and NASA to secure these communications services in order to support their upcoming lunar missions. As well as this, a few hosted payloads have been added to the spacecraft that will increase the scientific value of the mission. Lunar Pathfinder will enable both institutional and commercial missions to carry out data intensive activities around the moon, without the need for complex and costly on-board communication equipment and access to global ground networks. An ESA Moonlight Phase A/B1 study is also ongoing, investigating a full lunar constellation that will provide enhanced communication and navigation services. SSTL Lunar is a brand of SSTL created to promote, offer and deliver the future lunar communication and navigation services. An integral part of SSTL, it symbolizes the start of an off-planet service offering for lunar assets. Lunar Pathfinder falls under the small satellite class, with a mass of 300kg, and will operate in an Elliptical Lunar Frozen Orbit (ELFO), offering communication services to lunar missions of all types (orbiters, rovers, landers, stationary instruments). Due to launch and enter operation in 2025, the spacecraft will be in service for 8 years. This programme is supported by ESA under a commercial partnership programme. The Lunar Pathfinder services relieve some of the burdens faced by lunar missions using Direct to Earth (DTE) communications for transmitting data back to their ground stations. DTE requires a direct line of sight, making it impossible for communications on the far side of the Moon, and exposing the risk of communications interruption due to obstructing terrain - especially relevant for mobile assets. Lunar Pathfinder's orbit provides high availability communications for those missions on the far-side and polar regions, unlocking a plethora of exploration opportunities. The reliance of DTE on the Deep Space Network (DSN) presents further challenges. Subscription to the network is routinely over capacity, leading to limitations on the data-rate and contact times achievable, which subsequently affects the volume of data that can be transferred. As a consequence, the optimal scientific and commercial potential of these missions cannot be realised. With a store and forward capability, a proximity link, two simultaneous channels in S-band and UHF for lunar asset links, Lunar Pathfinder is designed to lift these constraints. It allows longer upload durations and improved data-rates with each of the lunar assets, enabling the bulk transmission of data back to Earth Ground Station, ready for distribution to the end users. An ESA GNSS receiver capable of detecting weak signals coming from the Earth GNSS infrastructure (GPS and Galileo), will be on-board Lunar Pathfinder, investigating the potential of GNSS in the future of Lunar navigation. A NASA retro-retroreflector is also hosted by Lunar Pathfinder, along with an ESA radiation monitor, contributing to the knowledge generation that will further support humanity's return to the Moon. To achieve a thriving ecosystem, the supporting infrastructure must be in place to enable sustainable evolution of nascent lunar markets into a mature industry. A critical pillar of this infrastructure is currently being investigated in a PhaseA/B1 study under ESA's Moonlight initiative, in the form of a lunar communications and navigation service, provided by a constellation of satellites. Building on the foundations of Lunar Pathfinder, an SSTL-led consortium, along with established telecoms operators and ground segment operators, are characterising the end-to-end architecture of the service. Collaboration and interoperability is essential for the sustainable future of the lunar economy, therefore this communication and navigation service is designed in harmony with other infrastructure elements such as Gateway and LunaNet. This allows the service to be easily leveraged by institutional, commercial and governmental users alike, enabling flexible communication and navigation capabilities, energising disruptive applications and business models.