Cooperative Radio Navigation for Robotic Exploration: Evaluation of a Space-Analogue Mission.

Autonomous robotic systems will play an important role in future planetary exploration missions. To allow autonomous operation of robots, reliable navigation is vital. Such a navigation solution is provided by cooperative radio navigation, where radio signals are exchanged among the robots. Based on the signal round-trip time (RTT) and direction-of-arrival (DoA), the robots' positions and orientations are estimated. Cooperative navigation has been well studied theoretically, but experiments mainly focused on indoor scenarios and other applications. For the first time, we have demonstrated cooperative radio navigation within a space-analogue exploration mission with two robotic rovers. The mission took place on the volcano Mt Etna, Sicily, Italy. During the first part of the mission, simultaneous localization and calibration (SLAC) is performed to improve the accuracy of RTT and DoA estimates by reducing the bias. Then, the rovers travel to a distant area of interest. Ultimately, one rover travels so far that it is connected to the network only via another rover. We find that even in this challenging single-link scenario, robust cooperative navigation is achieved. When the rovers are not further than 60m away from the lander, their position root-mean-square errors (RMSEs) are 0.3m to 0.9 m. Even for the most challenging mission phase, when the rovers are 100m to 160m away from the lander with single-link localization, the position RMSEs are 1.7m to 2.6 m. The orientation RMSEs of the rovers lie between 2.4 degrees to 6.1 degrees. Thus, with this spaceanalogue mission, we show that cooperative radio navigation for planetary exploration is robust and accurate.