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Space Station

Controlling Curiosity: How do you drive a Mars rover?

About the author

Richard is a science journalist and presenter of the Space Boffins podcast. He edits Space:UK magazine for the UK Space Agency, commentates on launches for the European Space Agency and is a science presenter for BBC radio. You can also follow him on Twitter or Facebook.

  • Mars Yard
    At Nasa’s Jet Propulsion Laboratory in California, engineers have access to two full size replicas of the Curiosity Rover. (Copyright: Boffin Media)
  • Test run
    The robots are used to help troubleshoot and plan daily missions for the real rover that landed on Mars two months ago. (Copyright: Boffin Media)
  • Mindless moves
    Scarecrow, so called because it has no “brains” is be driven around the ‘Mars Yard’ test area using an iPhone app. (Copyright: Boffin Media)
  • Game over
    ...unless a journalist is at the controls. Here, the author, inspects the machine after ‘grounding’ it on a rock. (Copyright: Boffin Media)
  • Mission critical
    Mars Yard has become essential for the 200 or so scientists responsible for planning daily missions for the real rover. (Copyright: Nasa)
  • Water way to go
    So far Curiosity has covered more than 300m (1,000ft) since landing, making various discoveries along the way, including evidence of an ‘ancient streambed’. (Copyright: Nasa)
Navigating a robot around a planet several million miles away is no small task, as Richard Hollingham finds out.

Engineers at Nasa’s Jet Propulsion Laboratory (JPL) in Pasadena, California,  have the ultimate iPhone app. But it’s not something you will find in the App Store. With a few taps on the screen, I can send a replica of Nasa’s Curiosity rover trundling - at a slow walking pace - across the rocky terrain of JPL’s outdoor test area, known as Mars Yard.

I find myself treating the experience like a video game: starting out cautiously with a few gentle turns, before commanding the car-sized rover to cross some sizable boulders. Mobility test engineer Daniel Fuller calls ‘game over’ when I manage to ground one of the vehicle’s six wheels on a particularly large lump of stone.

Thankfully the real rover, some 200 million kilometers (125 million miles) away on the Red Planet, is in safer hands. And the way it’s driven is rather different.

“It’s a common misconception that we’re just ‘joysticking’ it or we’re driving and sending these commands and we’re suffering a 15 minute delay,” says Fuller, who divides his time between the rover control room and Mars yard. “We actually plan an entire day – or a sol as it’s called on Mars.”

Each of these daily missions is overseen by people like Sanjeev Gupta from Imperial College London. When I meet him, the geologist and senior member of the JPL science team is living on Mars time.

“During the Mars night we prepare the sequences the rover has to do,” he explains. “Then we uplink those commands and, when the rover wakes up, it carries out those tasks. But a Mars day is 40 minutes longer than an Earth day so you get progressively out of synch, so the time I arrive at work changes by an hour every day.”

And that’s not all. “We don’t get a signal direct from the rover to Earth,” says Gupta. “It has to go through communications satellites - Mars Reconnaissance Orbiter (MRO) and Odyssey - and these obviously have different times [when they’re overhead].”

“Generally you’re moving an hour forward each day but suddenly, like tomorrow, I’m going to step back two hours. I’m progressively getting used to it but the first three weeks were awful,” he groans, “I was permanently exhausted.”

Unexpected plans

During the Martian night, dozens of scientists, including Gupta, anaylse the images and data coming back from the Red Planet and discuss what they want to do next. They hold a series of meetings to prioritise time on the instruments, choose which images to capture and where the rover’s going to move.

“It’s quite complicated because you have to work out how much power each instrument is going to use and how much heating time they require,” Gupta says. “Because they’re so many instruments, everybody wants to have a go – so one instrument might get five minutes, another ten minutes.”

Once the arguments are had and decisions reached, the drivers get to work, coding the next day’s instructions. And this is way more complicated than programming one of those ‘80s-era Big Trak robot toys.

Curiosity is the fourth rover (since the 1996 Pathfinder mission) Nasa has run on Mars in recent years, and the procedures have got better with every mission. Armed with 3D images from its navigation cameras, the drivers work through the Martian night to map out the best, smoothest, route to the next destination. They factor in any stops along the way, to take pictures or operate an instrument, and run a simulation of the journey to double-check they have got it right.

The aim is that when a new day dawns on Mars, the drivers are ready to go. Once either the Odyssey or MRO satellite is in the right place, they send a command to wake up the rover and upload its commands for the day. A bit like emailing a ‘to do’ list.

Gupta admits that the whole process is more time consuming than he first imagined. “Things that I can do in an hour on Earth, take days on Mars. Usually on Earth I work by myself, here we’ve got a team of 200 scientists so we have to work out these interactions and protocols.”

Once it’s started moving, Curiosity also has the ability to think for itself using data from its hazard avoidance cameras and built-in safely protocols. This autonomy should prevent it grounding on a rock or falling over an unexpected cliff but also adds to the pressure on the drivers and scientists planning each sol’s activities.

This is where the rovers in Mars Yard come in handy. This dusty outdoor arena at the back of the lab is around the size of a couple of tennis courts. Strewn with boulders, mounds of sand and even a cliff face, it’s home to two full-scale mock-ups of Curiosity. Although the real thing was tested extensively before launch, these rovers are still in use everyday by drivers trying to choreograph movement on Mars.

“We do have a pretty good idea how it’s going to perform,” Fuller confirms. “But these give us a chance, in flight, to modify and fine tune and to get as much bang for our buck as possible.” Specially, they allow engineers to test movements, software and work on any glitches that develop on the real thing.

The first rover is an identical copy of Curiosity; it’s even loaded with the exact same software. The second – and the one (for obvious reasons) they let me control – is not fitted with the same onboard computers, earning it the nickname Scarecrow, because it doesn’t have a “brain”. Although it’s the same size as Curiosity, Scarecrow is lighter, to simulate the effects of moving around in the lower gravity of Mars.

Scarecrow is little more than an impressively large remote controlled car. Scroll the tumblers to set distance and angle of movement on the iPhone app, hit go and it reacts instantly, there’s even a stop button if things start going awry.

Thanks to the efforts of its drivers and the engineering team behind them, Curiosity has covered (at the time of writing) more than 300m (1,000ft), including a single push of 42m (138ft), its biggest roll to date since landing on Mars two months ago. Despite being millions of miles away, it’s considerably further than I achieve before grounding Scarecrow.

“That’s the most fun a reporter has ever had with our rover,” says Fuller. I’m not sure he is paying me a compliment.

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