If you could stand next to NASA’s Perseverance rover on the Martian surface... well, you’d be standing on Mars. Which would be a pretty remarkable thing unto itself. But if you were waiting for the rover to go boldly exploring, your mind might soon wander. You’d be forgiven for thinking this is like watching paint dry. The Curiosity rover, which landed on Mars in 2012 and has the same chassis, often goes just 50 or 60 meters in a day.
Which is why Rich Rieber and his teammates have been at work for five years, building a new driving system for Perseverance that they hope will set some land-speed records for Mars.
“The reason we're so concerned with speed is that if we're driving, we're not doing science,” he said. “If you’re on a road trip and you drive to Disneyland, you want to get to Disneyland. It’s not about driving, you want to be there.”
Rieber is the lead mobility systems engineer for the Perseverance mission. He ran the development of the drivetrain, suspension, engineering cameras, machine vision, and path-planning algorithms that should allow the rover to navigate the often-treacherous landscape around Perseverance’s destination, called Jezero crater. With luck, Perseverance will leave past rovers in the dust.
“Perseverance is going to drive three times faster than any previous Mars rover,” said Matt Wallace, the deputy mission manager at NASA’s Jet Propulsion Lab. “We have added a lot of surface autonomy, a lot of new AI if you will, to this vehicle so that we can complete the mission on the surface.”
The rover, if everything works, will still have a maximum speed of only 4.4 cm per second, which is one-thirtieth as fast as human walking speed. It would travel the length of a football field in 45 minutes. But, says Rieber, “It is head and shoulders the fastest rover on Mars, and that's not because we are driving the vehicle faster. It’s because we're spending less time thinking about how.”
Perseverance bases much of its navigational ability on an onboard map created from images taken by NASA’s Mars Reconnaissance Orbiter–detailed enough that it can show features less than 30 cm across. That helps tell the rover where it is. It then adds stereo imagery from two navigational cameras on its top mast and six hazard-detection cameras on its body. Each camera has a 20-megapixel color sensor. The so-called Navcams have a 90-degree field of view. They can pick out a golf ball-sized object 25 meters away.
These numbers add up: The technology should allow the rover to pick out obstacles as it goes—a ridge, an outcropping of rock, a risky-looking depression—and steer around many of them without help from Earth. Mission managers plan to send the rover its marching orders each morning, Martian time, and then wait for it to report its progress the next time it can communicate with Earth.
Earlier rovers often had to image where they were and stop for the day to await new instructions from Earth. Curiosity, on days it’s been ordered to drive, only spends 13 percent of its time actually in motion. Perseverance may more than triple that.
There are, however, still myriad complexities to driving on Mars. For instance, mission engineers can calculate how far Perseverance will go with each revolution of its six wheels. But what if the wheels on one side slip because they were driving through sand? How far behind or off its planned path might it be? The rover’s computers can figure that out, but their processing capacity is limited by the cosmic radiation that bombards spacecraft outside the Earth’s protective magnetosphere. “Our computer is like top of the line circa 1994,” said Rieber, “and that’s because of radiation. The closer [together] you have your transistors, the more susceptible they are.”
Matt Wallace, the deputy project manager, has been on previous missions when—sometimes only in hindsight—engineers realized they had barely escaped disaster. “There's never a no-risk proposition here when you're trying to do something new,” he said.
But the payoff would come if the rover came across chemical signatures of life on Mars from billions of years ago. If Perseverance finds that, it could change our view of life on Earth.
Is there a spot somewhere at Jezero crater that could offer such an incredible scientific breakthrough? The first step is to drive to it.