There is something rather satisfying about seeing photos of human technology exploring alien worlds, whether it’s the glint of rovers on rocky plains seen from orbit or their tracks trailing off into dusty, desolate landscapes. None of this, though, compares to the satisfaction of all the scientists and engineers in seeing the fruits of their work.
Craig Leff is a researcher who has worked (amongst other things) as a systems engineer on the long-lasting Mars Exploration Rovers (Spirit and the extant Opportunity), and is involved with the upcoming ExoMars Rover project for the European Space Agency. His wife has worked on the Cassini probe missions to Saturn. I got the chance to speak to both of them afterwards and I hope I didn’t geek out too much. At the very least, I learnt that my game of Kerbal Space Program barely hints at the complexity of running a real space mission.
Craig was an engaging speaker with far more to talk about than time allowed (isn’t that always the way with interesting speakers?); he very generously stayed in the bar for further talk and questions afterwards. I was interested to learn that a lot of software written decades ago was still in use – not just for communicating with old probes like Voyager, but also for things like air traffic control. There’s simply never been a need to replace it!
Working On Mars
In his talk, he described what it takes to get a machine the size of a Mini and the weight of a walrus to land on another planet and drive around at a snail’s pace using no more power than you’d find in a couple of desk fans.
Unlike the Soviet Lunokhod moon rover missions of the 1960s and 70s, the Mars rovers cannot be driven with joysticks – a time delay of 10-20 minutes between Earth and Mars makes this impossible. Rover missions also differ from other space probes, in that probe missions allow a lot of time for planning while they travel through space on pre-determined trajectories. Rovers can find their own way around Martian terrain (‘Autonav’ mode), but they need daily commands programmed into them, as scientists and engineers react to events and set precise targets. An error in a probe mission may result in a fly-by that misses opportunities for study that can never be regained; a rover can use its cameras to check its position and speed against landmarks (‘visual odometry’), and any problems with the route can be dealt with by the team on Earth. The longest single drive was 220 metres in a single Martian day (or ‘sol’) .
At the end of each sol, the rover transmits its findings and records of its movements back to Earth, before the sun stops shining on its solar panels. This is when the mission team begins their work. What did it accomplish? What was it unable to do? What state is it in?
The scientists have to meet (or cage fight) to prioritise the tasks and experiments for the following sol. The engineers have to figure out what the rover is physically capable of given its limited time, travelling distances, resources, and safety concerns. All of these must be put into the most efficient sequence possible, and the commands programmed; planners run simulations to see if all this is possible. If it is, then the person known as ‘ACE’ transmits the commands at the following Martian dawn, when the rover wakes up. (Nobody’s sure if ‘ACE’ is an acronym, or a nickname…)
All of this analysis, planning, sequencing and programming happens day after day for as long as the mission lasts (90 days minimum; Opportunity has lasted 3745 sols at time of writing – way more than a decade!). Each member of the team has to keep a record of what they’ve done, in case anyone has to take a day off and others need their data.
But there’s one more wrinkle to consider: a sol is 40 minutes longer than a day on Earth. The team will often find itself starting (or finishing) work in the early hours of the morning. Some – including Craig – wear ‘Mars watches’ set to run 40 minutes slow. Being out of synch with Earth time plays hell with everyone’s body clocks, as well as their social, personal and family lives (understandably, many choose to work from home when possible – but everyone turns up for the big milestones, such as the landings).
So when you see those photos taken from the surface of Mars, bear in mind that they represent feats of endurance of not just the machines, but also the community of people who operate them!
PS: Although I don’t have a Twitter account, I did have a look online at the @SarcasticRover account, which is good for a laugh…