Move over, rover
UK researchers are developing the protocols that will be used to help autonomous robotic rovers retrieve samples from distant celestial bodies in future exploration missions
The room is a strange mix of hi-tech and institutional. One entire wall is taken up by a giant collage of video screens; the others are the usual alumiunium-framed plasterboard. An array of laptops sit open on standard-issue office tables; thinly-cushioned chairs litter the floor, doubtless less comfortable than they look. It’s a long way from the sleek bustle of the Mission Control suites we’re used to seeing on broadcasts of big space missions.
Yet the video wall is showing eerie scenes of an empty, rocky landscape with wheel tracks in the dust, and occasionally the characteristic blocky shadow of a planetary rover appears, topped with the wavering stalk of its sensory array. Graphs and diagrams skitter across the screens, and plots of routes to target locations.
But this isn’t a Mars mission, or even lunar. This is a room at the Satellite Applications Catapult on the Harwell Innovation Campus near Oxford, just over the road from the giant, furutistic silvery doughnut of the Diamond Light Source; it’s the control room for a project called SAFER, a contrived acronym for Sample Field Acquisition with a Rover. And the location on the video wall is remote and hostile, but it’s not extra-terrestrial; in fact, it’s in Chile, near the European Southern Observatory’s Paranal site in the Atacama Desert.
Although the shadowy rover in the trial is Bridget, one of the European Space Agency’s test-beds for technology to be used in the upcoming Russo-European ExoMars mission, SAFER isn’t specifically a Mars mission. Instead, it’s a deliberately generic attempt to develop protocols for gathering samples with a rover on any space mission, whether it’s to the moon, Mars, an asteroid, or one of the rocky satellites of the Solar System’s gas giants, all of which are planned for the next decade. A major part of the mission is to test out routines for planning a rover’s daily activities, sending its mission profile and allowing it to use its on-board sensors and autonomous control systems to work out its own routes to sites of interest. During a mission, this data would be relayed from Ground Control to an orbital satellite and down to the rover; for SAFER, an on-site team at Paranal is acting as the satellite. It’s also acting as the rover’s drill; for this mission, unlike a previous one to the equally arid volcanic plateaux of Tenerife, Bridget is drill-less.
“We’re particularly interested in looking at sheltered spots – in the lee of large rocks, for example — because that’s where evidence [of life] is most likely to be preserved
Lester Waugh, EADS Astrium
Despite the generic nature of SAFER, with ExoMars the biggest milestone mission on ESA’s schedule, Mars loomed large on the planning of the project. The Atacama was chosen because of its close similarity to the Red Planet’s landscape: one of the driest places on Earth, it has no vegetation and similarly-sized rocks, and very few man-made objects or structures. Despite this, the proximity of Paranal and its facilities made it a convenient place for the remote team’s base.
It also has very unpredictable weather, including dust-devils and and high winds. At one point, the desert team witnessed the gazebo sheltering their on-site equipment go cartwheeling across the Atacama, and had to hastily set-up a temporary refuge behind some parked cars.
The rover itself also has a Martian mission set-up, carrying three instruments destined to fly on the ExoMars mission. The vehicle — build at EADS Astrium’s Stevenage factory — was carrying a panoramic camera atop its pylon, to give a view similar to the point of view of a human explorer; a close-up imager which provides pictures similar to those from a geologist’s lens; and a ground-penetrating radar to help locate likely underground drilling targets. The team’s excavation activities, ordered by the Harwell site, helped to confirm the accuracy of the radar data.
This is particularly important for ExoMars because the mission’s main goal is to locate and identify samples which could indicate the presence of past life on Mars. ‘As Mars has only a thin atmosphere and no magnetic field, it’s bombarded by strong radiation from the sun, and we know that’ll degrade any of these life-characteristic compounds on the surface,’ explained Lester Waugh, who leads Astrium’s ExoMars activities. ‘The mission is going to concentrate on areas where we know there will have been flowing water in the planet’s past, because those are the conditions which will have been the most conducive to the development of life forms, and we’re particularly interested in looking at sheltered spots – in the lee of large rocks, for example — because that’s where evidence is most likely to be preserved. We think that 60cm to 2m down, the overlying soil and rocks will have provided enough shielding from radiation for us to find these organic compounds — if they’re there.’
Results so far have been encouraging. ‘At our second simulated drilling location, the field team found a layer of rock at a depth of 60cm,’ said Sev Gunes-Lasnet, project manager in the Atacama for Rutherford Appleton Laboratory (RAL) Space, the lead organisation for SAFER. ‘This comes close to the kind of features the team was looking for: analogues of locations on Mars which could hold traces of present or past life.’
The autonomy of the navigation systems on Bridget was an important part of SAFER. Because in an actual extra-terrestrial mission any contact with the rover would be sporadic, depending on the alignment of Earth, the orbiting communications satellite, and the rover itself on the surface, the idea behind the mission is that ground control identifies likely-looking targets based on satellite imagery and tasks the rover at the start of each day with the location it is to investigate.
But because the resolution of the satellite imagery is not fine enough to identify all the possible obstacles on the way, the rover can interpret the imagery from its own cameras and what it picks up from the interaction between its wheels and the ground to plan its own routes. If it finds itself in an impassable position, it’ll just stop and wait for instructions, which would take another whole Martian day (or ‘sol’) to get there. So to avoid wasting valuable mission time — or worse, putting the rover into a situation which might damage it or otherwise render it useless, like sending it over a cliff, into a ravine or flipping it over, it’s vital for the autonomous guidance systems to be as good as possible
This created a few unusual activities for the ground team. To make sure that the rover had an accurate experience of navigating, they had to get rid of anything which might have given the system clues it wouldn’t have it were alone on an alien planet. That meant getting out with a broom and carefully brushing away any tyre tracks from support vehicles and their own footprints, leaving the desert surface as pristine as they could manage.
It also pointed out some literal potential pitfalls. At one point, Bridget’s front wheel flipped over a flat rock, creating an impassable barrier that hadn’t existed before — Astrium’s rover design team will be taking this into account for their next design phase for the ExoMars rover itself.
ExoMars is due to lift off in 2016, and the results of the SAFER trial, which are now being evaluated at Harwell, will feed into planning the detail of the mission; particularly where it will land and explore. It needs to be near the equator, because the rover will be solar-powered (unlike NASA’s Curiosity rover which has a nuclear powerpack) and will need to be suitable for landing, movement and testing — a tricky combination. Locations with iron- and magnesium-containing clays are a likely target, as these minerals betray the location of long-vanished water. A working group is expected to be announced later this month, with a decision due by the middle of next year.