He remembers going home afterwards: "I'm lying there, looking at the ceiling, realizing there's a robot on another planet doing what I told it to. And that notion of, 'I'm getting to do this. I'm not dreaming about this anymore. It's real for me now.'
"I reach out across 100 million miles of emptiness and move something on the surface of another planet. That feeling has never left me."
The opportunity to drive
You might think a rover driver would control the vehicle using a joystick and virtual reality interface, much like a video game. That's not how it works. The reason for that: Signals take at least four minutes to travel from Earth to Mars (it could take up to 20 minutes, depending on where the planets are in their orbits), and then the same amount of time for confirmation data to come back.
So rover drivers don't tell the vehicle to move forward and then wait several minutes for confirmation that it happened before sending the next command. Instead, drivers spend their days writing directions for what the rover will do the next day, sometimes even a few days if it's a holiday weekend.
Maxwell and colleagues spend the Martian night generating a single batch of commands, which they send to the rover after the vehicle sees sunrise. Drivers work in overlapping 8- to 10-hour shifts preparing the rover for the day ahead. "It's as if we're e-mailing the rover its to-do list for the entire day," Maxwell explains. And at the end of its day, the rover sends information back saying what it did. During the Martian night, the rover goes to sleep.
That might sound risky, letting a vehicle roam around on a planet for several hours without someone guiding its every move in real time. But safety checks are built in. Curiosity will know how far its wheels are moving up and down, so it will stop if it heads into something deeper or higher than the drivers had planned. In that sense, the rover is more like a boat than a plane -- stopping is a fine course of action if additional direction is needed, Maxwell explains.
Curiosity can travel up to about 2.5 meters (8.2 feet) per minute, says rover driver John Wright, but in practice it will go a lot slower because the science team will want it to stop and examine its surroundings. A rover may stop and take photos, or -- as will be the case with Curiosity -- the scientists will want it to stop to perform chemical analyses.
Photos the rover takes of its surroundings help the drivers determine where to send it next. The drivers use a 3-D simulation created from the photos to visualize what the rover is seeing. The virtual model of Mars lets drivers work out which commands to transmit each day. Video games have helped several rover drivers hone their skills, including Maxwell, since driving on Mars requires planning and multidimensional thinking.
Any game that shows a large open world, such as "World of Warcraft," can hone these skills, says Cooper, the first rover driver and the only person to have driven all three rovers NASA has landed on Mars.
"You're essentially driving a robot with a keyboard 100 million miles away," says Maxwell. "You can't always believe what the simulator tells you. If anything does go wrong, there's no one there to hit the panic switch."
Besides being manually controlled, the rover also has the capability to drive by itself, detecting hazards through cameras and driving around them. This autonomous mode takes more time, however, so it's employed less often.
Curiosity landed in Gale Crater, where it may find evidence the area once was a lake. It will take at least a year to drive Curiosity to its ultimate destination, Mount Sharp, where the rover will examine layers of sediment for organic molecules, which would be signs -- but still not proof -- that life may have existed on the planet.
Maxwell will see some of the images Curiosity takes before anyone else does, but he loves that the public will get to view them soon after on NASA's website. "I get to take everybody in the world along in the backseat," he said.
Beyond rover driving, Maxwell genuinely loves the science of Mars. The rover science team has its own busy agenda, but during the mission involving Spirit and Opportunity, Maxwell would point out rocks that might be interesting to examine further, or suggest photographing the sunset on a given day. Sometimes the science team would take him up on his ideas.
"He's always looking to try to get as much out of the vehicles as possible," says Squyers, lead scientist of the Mars Exploration Rover mission, which involved Spirit and Opportunity. "Scott is, within the bounds of safety, one of the most enthusiastic rover drivers there is."
The spirit of his first car
There's a special love that Maxwell has for Spirit, the first rover he ever drove. Spirit was only supposed to last about 90 days, but the rover kept operating for more than five years.
When Spirit got stuck in May 2009, Maxwell felt like he was in an Indiana Jones movie, trying to rescue the vehicle. The rover's wheels broke through a crust and the vehicle fell into a sandy trap called Troy, like a car driving into a pool of flour. Even before the accident, one of its six wheels had quit working.
Maxwell and his colleagues were almost able to pull Spirit out, but not quite. They had figured out a technique, but with the Martian winter coming, the solar panels were tilted away from the sun. Plus a second wheel malfunctioned during escape tactics. Over the winter, something broke -- Maxwell says humanity may never know what.