ESA’s scientists have successfully tested navigation software for the ExoMars 2020 mission, putting it through a rover-based driving test. The team used the ExoMars Testing Rover (ExoTeR), which is a half-scale version of the rover that’ll traverse the Red Planet, to check the navigation software during the two-day-long rover trials.
At ESA’s 9 x 9 m “Mars Yard” testing facility at the ESTEC, Netherlands, ExoTeR calculated its route as it maneuvered around rocks at a rate of 2 m per minute. According to the ESA, the actual ExoMars rover will drive much slower, progressing 100 m per Martian day.
Independent navigation is key to the mission’s success, since “The enormous distance from Earth to Mars equals a signal delay of between four and 24 minutes, making direct control of ExoMars impractical,” according to the ESA.
“Rather than sending complete hazard-free trajectories for the rover to follow, autonomous navigation allows us to send it only a target point,” says ESA Robotics Engineer Luc Joudrier. “The rover creates a digital map of its vicinity and calculates how best to reach that target point. Looking at the map it tries to place the rover in all these adjacent locations to work out if the rover would be safe in every one of these positions—or if the rocks are too high or terrain too steep.”
The rover uses the local navigation map to compute the safest path toward its target destination, moving along a segment of the calculated path, explains Joudrier. The mapping process repeats at the end of the segment.
“It is similar to a human walking. We look ahead to decide where we are going but as we walk we peer down at our feet and if necessary change course to avoid obstacles. Once we have chosen a path without obstacles, we make sure we follow that path to remain safe,” says Joudrier.
Just like the ExoMars rover, the half-sale test vehicle carries mast-mounted stereo navigation cameras that are used for digital elevation mapping. A pair of cameras on the front chassis will also continually check the rover’s progress.
This vision-based motion tracking is more favorable “than simply measuring the turn of the rover’s wheels because it allows controllers to take account of any wheel slippage—rovers on Mars have previously been caught in deep sand, and continued wheel turning might actually dig them in deeper,” according to the ESA.
The ExoMars rover, which will end up having two sets of autonomous navigation software, will drill down 2 meters below Mars’ surface at different location, searching for signs of preserved life.
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