How Are Mars Rovers Driven? Planning, Autonomy and Signal Delay
Nobody steers a Mars rover live. Here is how rover drivers plan each drive, why signal delay makes joysticks useless and how autonomous navigation works.
Driving a rover on Mars looks nothing like driving a remote-controlled car. There is no joystick and no live video. Instead, rover drivers on Earth plan a whole day of driving in advance.
The problem: distance
Depending on where Earth and Mars are in their orbits, a radio signal takes between about 3 and 22 minutes to travel one way. By the time you saw a rock in a live video and pressed "stop", the rover would already have hit it.
A day in the life of a rover driver
- Look. Overnight the rover sends down images from its cameras. The team builds a 3D model of the terrain around it.
- Plan. Rover drivers, officially called rover planners, mark a route and safe stopping points, often using 3D goggles to inspect the ground.
- Simulate. The commands are tested in software so that nothing unexpected happens.
- Send. The plan goes up to Mars, usually once per sol, and the rover carries it out on its own.
Autonomous driving
For longer drives, rovers use autonomous navigation. The rover takes stereo pictures, builds a map of hazards ahead, picks a safe path and drives a short step, again and again. Perseverance's AutoNav can do much of this processing while moving, which lets it cover more ground than earlier rovers.
How Trawers does it
Trawers borrows the same idea. You can plan a route on the map and let the rover follow it in real time, even when you close the game, or switch to direct driving with WASD or the arrow keys for short moves. The rover is faster than the real one, but the planet is the same size, so planning still matters.