NASA will land its next rover, Perseverance, on the surface of Mars in February of 2021, and an engineer on the Curiosity rover pilot team just opened up about what the process is like.
There's roughly a 22-minute signal delay between earth and mars, meaning that piloting the craft over unknown terrain requires some unique planning. Evan Hilgemann, a NASA engineer that was selected to serve on the team of engineers that piloted the Curiosity rover, recently wrote a Medium post opening up about what the experience was like.
His goal in writing the post wasn't just to share his unique story, but also to give everyone watching Perserverence drive across the red planet a little background on what's going on behind the scenes.
The first thing Hilgemann notes about piloting the rover is that "Curiosity only receives information from Earth once a day and is on its own the rest of the time." So how does his team even pilot the rover if it only gets information once a day?
Piloting the rover
For starters, the rovers are covered in 3D-cameras that allow an accurate picture of all of their surroundings. With the sensors on-board, the rover is able to do plenty of tasks autonomously, like pick up and scan rocks with its onboard laser or drive around in pre-planned patterns. However, the robot sometimes gets stuck and when that happens, generally it holds tight until it gets more instructions from the green planet.
The person taking the lead as the rover driver at any given time has the responsibility of keeping the rover safe. Accomplishing this goal successfully means being able to see where you're going. The team of engineers is able to develop a virtual image of the rover's surroundings using navcams and hazcams. The hazcams are onboard cameras that spot nearby hazards, like rocks or ledges, and the navcams focus in on further distance surroundings for locational plotting.
As for sending the rover its instructions once the engineers get a clear picture, the team has a few options. They can send information in blind driving mode. Hilgemann notes that "blind driving is the simplest form of navigation available. In this mode, the rover will follow the specific instructions given to it but will not make any adjustments based on actual progress."
Another method is "Visual Odometry", which Hilgemann notes is the most common method used. This method essentially involves the rover taking pictures at regular intervals, about every meter, then comparing the images to previous pictures to see where it's moved and how the terrain has changed.
Finally, the most high-tech of driving the techniques is called "autonav," in which the rover can only cover about "100 feet in an hour." This mode is like self-driving in vehicles. Utilizing its onboard hazcams and navcams, the rover can develop an image of its surroundings and autonomously map out safe paths. The composite image the rover develops looks like the image below, with the various colors indicating safe (green) or hazardous (red) terrain.
Perseverance's next steps
Assuming everything goes according to plan for Perseverance in February, the rover will begin being piloted by its crew using one of the three methods Hilgemann described. However, there is a significant risk that the rover won't reach the surface. The descent and landing phase of the drone is by far the biggest opportunity for catastrophic failure in the mission.
One note Hilgemann adds about the new rover is that it's sort of a speed demon compared to Curiosity. He adds, "the new rover will generally be able to drive at least twice as fast as Curiosity thanks to new dedicated computing resources and better algorithms. Perseverance’s navigation cameras are also in color and higher resolution," than Curiosity.
Perseverance is set to land on Mars on February 18, 2021.