ALIX: a radio interferometry based location tracking system for pioneering astronauts on Mars

In the context of planetary exploration, precise local navigation solutions are critical. Currently there is no satellite network available on Mars that can facilitate navigation. Current methods of navigation on Mars use for example accelerometers, gyroscopes and celestial positioning. These methods lead to large errors in location over time. The Astronaut Location Interferometry eXperiment (ALIX) proposes an alternative way of navigation for early Mars exploration. ALIX aims to perform live location tracking of astronauts or vehicles using a compact mobile radio transmitter and an array of receiver stations. Meter-scale accuracy is expected over a tracking range of a few kilometres. The system can be deployed from a landing site. The tracking range can be extended by deploying additional receiver stations further away from the landing site, making this a very scalable solution. The proposed localisation method makes use of a technique called interferometry, commonly used in radio astronomy. The astronaut is equipped with a transmitter broadcasting a continuous radio signal. Various receiver stations measure the phase of the received signal every second. This received phase is dependent on the location of the source, time of transmission and time of measurement. Using phase differences between antennas, the location of the source is reconstructed. A minimum of three receiver stations is needed for successful tracking, with the use of more receivers adding range, robustness and accuracy. The different receiver stations can be synchronized using stationary beacons or a local Wi-Fi network, keeping the localisation accurate over time. Multiple astronauts and vehicles can be tracked at the same time by providing each with a transmitter broadcasting a unique frequency. ALIX will be tested during the AMADEE-24 mission. Ultimately ALIX will be developed into a reliable system for limited-range location tracking, easily deployable by pioneering missions using minimal recourses and infrastructure.