FOR the past nine years Scott Maxwell has worked on Mars. Or at least as close to it as is possible on Earth. This, it turns out, is Pasadena, California, home to NASA's Jet Propulsion Laboratory (JPL), which manages many probes, rovers and satellites for America's space agency. From there Mr Maxwell has driven three Mars vehicles: Spirit and Opportunity, twins dispatched in 2004 as part of the Mars Exploration Rover (MER) mission, and, more recently, Curiosity, which touched down on the planet last August carrying Mars Science Laboratory (MSL).

Of course, you don't just take Curiosity out for a spin. Mr Maxwell, who helped develop the driving software for the MERs and later became their principal pilot before moving on to direct the newer set of wheels, explains that you need to put yourself in the rover's head. This lets you picture and plot moves before typing the computer code that is then beamed to the vehicle. On February 8th, he announced a few days ago, he plans to shed the robot suit and resume his human life, but not before having trained other chauffeurs in the same mental gymnastics.

The MSL driving team comprises 16 operators, divvied up into groups specialising in mobility, moving the arm (to blast rocks with a laser to study their chemical composition and to take close-up photos) and managing the turret on the arm that houses a percussive drill. They drive the rover and deploy its instruments as instructed by the mission team, which meets each Earth day to decide, through consensus, where it should go on the following Mars day, or sol, and what science it should perform there.

Mr Maxwell, a member of the mobility team, demonstrates to your correspondent how he might move his hand in sympathy with the rover's multi-jointed wheels to think through the physical sequence. A computer scientist, Mr Maxwell then plots the route in software he developed that translates the driving sequence into commands that the on-board computer understands. But before instructions are beamed to one of two NASA satellites orbiting Mars, and thence to Curiosity, Mr Maxwell and his colleagues feed them into a simulator. Curiosity's several pairs of cameras—Mr Maxwell jokes that it has "more eyes than a potato"—provide stereoscopic images that let the boffins at JPL get a feel for the Martian landscape. This makes it easier to plan and test movements on a computer.

In particularly tricky situations when computer models fall short, JPL turns to another sort of in silico simulator. Its "sandbox", a pit of gravel and other materials mimicking the Martian regolith, can be used painstakingly to test how an identical copy of Curiosity would fare. JPL also has a full-scale but stripped-down model, adjusted for the difference in Earth's and Mars's gravitational fields. Both versions test less tricky manoeuvres in a large outdoor space called the Mars Yard. (A simulacrum of Opportunity also sits in the sandbox's corner, waiting to be deployed as needed in either arena.)

In MSL's early days last summer, recalls Michael Watkins, the mission manager, his team was protective of the rover and chary of doing too much, too fast. Increasingly though, scientists leave Curiosity to its own devices. It is more autonomous than Opportunity, now nine years into its 90-day mission, and growing more so as roboticists figure out new ways to let it roam without direct supervision.

The human drivers need not fear for their jobs just yet. Dr Watkins says the team balances exploring more territory and geology, where increased autonomy allows greater range, with scientists' desire not to miss anything important, where human discretion continues to be paramount. As for Mr Maxwell, he has yet to decide where to go next, though he admits that "driving on Mars" will be tough to top. But his face brightens when talk turns to manned missions to the fourth planet. Should the venture materialise in his lifetime—and this is far from assured—Mr Maxwell says he would vie for a place. Even if it were just a one-way trip.