NASA’s Curiosity is the largest rover in operation on Mars. It is the size of a Mini Cooper, looks like an enormous robotic insect and moves at a snail’s pace. But don’t be fooled by its ungainly appearance or seeming lethargy: Curiosity’s off-road abilities are peerless.
So what can Mars rovers and Earthbound vehicles learn from each other?
“We are not good at this yet,” says Rob Manning, the chief engineer for the Curiosity Rover, now managing NASA’s Mars Program Engineering Office. He contends that there is a plenty of room for technological advancements, suggesting that a technology transfer could occur to make the next generation of earthbound and Mars-roving vehicles even better. Manning identified four key areas where Earth and space vehicles intersect.
The Curiosity Rover is built on a “rocker-bogie” drive system. There are no axles sending power to the wheels, or springs at the corners. “Our rover has six wheels, and the wheels are interconnected through pivots,” says Manning. “If you lift one wheel, the other wheels go down on that one side, and if you lift it high enough, you can transfer motion from one side of the vehicle to another.”
Imagine a child’s hanging mobile, with several independent but interconnected elements, and you’re not far off. That connected mobility helps shift the vehicle’s centre of mass, and means that the rover can move over objects – in Curiosity’s case, rocks – that are twice the diameter of a wheel, while keeping all six wheels on the ground. A typical SUV, by contrast, has independent wheel travel, but cannot climb over a rock more than about half its wheels’ diameter.
If the rover’s off-road capabilities are so superior, why don’t we see similar tech on SUVs (notwithstanding Mercedes-Benz’s bonkers G63 AMG 6x6)? There are some limitations. Connecting the wheels sacrifices the ability to drive dynamically, at high speeds. Curiosity’s top speed is about 4cm per second (that’s 0.144kph, or 0.089mph). “That is faster than a slug, but not much,” Manning concedes. “This design enables us to traverse the kinds of surface that a Jeep could never climb over, but at the same time we’ll never ever beat a Jeep on speed.”
We can fill our cars with gasoline (or just about any other combustible fuel), or we can plug them into the wall, here on Earth. Rovers on other planets have no such luxuries, requiring them to generate their own energy with either solar panels or, in Curiosity’s case, through an onboard nuclear power system. The rover carries a couple of kilograms of plutonium-238, which it uses to generate around 110 watts of electricity. The plutonium-fuelled powertrain is known as an RTG, or Radioactive Thermoelectric Generator, and it could go on providing power for over 10 years with no maintenance, no refuelling and no emissions (notwithstanding the leftover radioactive material). They sound like the sort of characteristics we would all like for our cars, but to put the power generation into context, the RTG makes 0.1kW per hour. It would take 850 hours, then, to generate the same amount of power stored by a Tesla Model S’s 85kWh battery pack.
That has not prevented vehicle designers from dreaming of an atomic car. In 1958 Ford unveiled the Nucleon scale-model concept car, with a reactor in the back. More recently a young designer named Loren Kulesus presented renderings of the Cadillac World Thorium Fuel Concept (or as Top Gear called it, the WTF concept), designed to run for 100 years with no maintenance.
The Curiosity rover copes with the RTG’s low power output by storing that energy in batteries, and then using it for bursts of activity like moving or snapping photographs. “This rover sleeps far more than it’s awake,” says Manning. Curiosity uses the same type of lithium-ion batteries found in most next-gen electric cars, including the Tesla – batteries that NASA had a hand in inventing. Together with the automotive and consumer electronics industries, the space agency continues to develop energy storage technologies. And because what is good for a rover is good for an electric car, all parties stand to benefit. (For more on battery tech, visit BBC Future.)
The Ford Model T was available in any colour as long as it was black. It seems that planetary exploration rovers are at about the same stage of design as that automotive relic. They’re available in any style as long as it is boxy, with compulsory gold-foil trim. They are certainly not sleek, but as Manning says, with a bit of deadpan, “There is no need on Mars for aerodynamic features.” Mars has around 1% of Earth’s atmosphere, so there is no air to push through. In fact, Curiosity does not have a nose or tail, per se; it can be driven in any direction.
After ground clearance, one of the most important design considerations is protection from heat and cold. It can reach a mild 20C (68F) on Mars, but a more typical temperature is about -50C (-58F). Forget heated seats and windshield defrosters. A Mars rover is like a giant Thermos flask, designed to keep the electronics inside as warm as possible.
Mars explorers do not drive at night, so Curiosity does not require headlights, though it does have small lights at the end of its robot arm. It also lacks windshield wipers. Mars is a dusty place, however, and accumulated grit can quickly coat camera lenses and incapacitate sensitive instruments. Fortunately, the occasional Martian windstorm, even in the very thin atmosphere, keeps the rover’s body clean.
The Grand Challenge autonomous-car competition, funded by the US military’s Defense Advanced Research Projects Agency (DARPA), has pushed robot cars towards the mainstream. And in projects such as Google’s driverless-car programme, the technology has developed at such a rapid pace that it has overtaken anything NASA has used. On Earth, the benefits of cars that avoid collisions or warn the driver of upcoming obstacles are obvious, but on Mars a degree of real intelligence is crucial for a vehicle. Remote control by a human operator on Earth is not practical, as signals can take around 20 minutes to reach the red planet.
Consequently, Curiosity utilises mobility algorithms which, when NASA developed them in the late ’90s and early 2000s for the Mars rovers Spirit and Opportunity, were cutting-edge. But even in the three years since Curiosity launched from Cape Canaveral, Florida, the intelligence of driverless cars has increased exponentially. “The technology, especially the control systems, has really allowed for an explosion of vehicle capabilities that has left us in the Martian dust, literally,” says Manning.
NASA intends to deploy its next Mars rover in 2020, and the European Space Agency is planning the launch of its ExoMars mission in 2018. Both are likely to benefit from advances in passenger-vehicle autonomy. “We would like to push that technology better,” says Manning. “You can imagine many new features.”
Interesting times, these are, when the space cowboys look to the street, not the stars, for the next big thing.
Just how big is space? Our colleagues at BBC Future have done some exploring. Click the image above to be taken on a journey through space and time.