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Members of the SAFER team helping set up rover Bridget in Chile. Credit: Elie Allouis ‎(Astrium) Members of the SAFER team helping set up rover Bridget in Chile. Credit: Elie Allouis ‎(Astrium)

Bridget is put through her paces in Mars-like desert

Sen— A British-built robotic rover designed to explore Mars began tests this week in the closest martian environment on Earth, the Atacama Desert.

The six-wheeled runabout, called Bridget, was designed and assembled by the UK wing of aerospace giant Astrium at Stevenage to help prepare for the European Space Agency’s ExoMars mission.

After years of tests and preparations in the laboratory and local sandpits, the rover prototype was sent to Chile where the red desert bears a remarkable resemblance to images sent back of the martian landscape.

The Atacama is one of the driest places on Earth and lacks vegetation, plus it has few man-made features such as roads and buildings. This makes it a perfect testbed. This weeks trials, due to last seven days, were dubbed SAFER (Sample Acquisition Field Experiment with a Rover) and are being carried out close to the European Southern Observatory’s Paranal Observatory.

As Bridget makes its first tracks in the sand in Chile, parallel testing is taking place from the UK’s remote control centre based at the Satellite Applications Catapult Centre in Harwell.

ESA got together an international industrial team to work with Bridget in Chile and so gain experience in operating a rover equipped with three of the scientific instruments that will fly on ExoMars. They include participants from ESA, the UK Space Agency, RAL Space, SCISYS, Astrium, Space-X, LATMOS, Joanneum Research, UCL, Aberystwyth University, University of Leicester, and Satellite Applications Catapult, Harwell.

SAFER is assessing the effectiveness of the mission’s rock outcrop search instrumentation, mimicking techniques that will be used on Mars to search for outcrops and then acquire samples of sand and rock.

On Tuesday, the three ExoMars instruments were fitted to Bridget. A panoramic camera provides stereo 3D terrain imagery, the close-up camera gives high-resolution imaging, and the radar peers through soil for a detailed 3D view of the shallow subsurface.

The scientific instruments used in the tests are designed to help search for the best places to drill down to collect samples from beneath the surface of Mars. Sheltered from surface radiation and harsh oxidising chemicals, these are the samples that might contain signs of past or present life.

Bridget makes tracks

The rover makes tracks, despite obstacles in the desert. Credit: Elie Allouis ‎(Astrium)

The team’s first task was to explore the region from the air, flying a drone to produce an aerial map that would help them to select a suitable site for testing and so plan Bridget’s route.

Michel van Winnendael, who is overseeing the testing for ESA, said: “During the past few days we have been busy preparing for the actual trial. A number of sites have been visited, based on guidance provided by Chilean geologist Professor Guillermo Chong.

“Our team geologist Derek Pullan, of the University of Leicester, has been exploring the area looking for similar sites to the kind of martian locations we would employ the same instruments on. The local team settled on a consensus choice – which we have christened ‘SAFER Valley’.

“Then on Sunday night a digital elevation map, acquired in the field by an overflying drone to simulate orbital imagery of the rover’s surroundings, was sent to the Remote Control Centre at the Satellite Applications Catapult facility in Harwell, UK.”

Before Bridget was deployed in the field, panoramic images were sent to the Harwell control centre where the remote control team had to decide on the path the rover should take the following day.

Michel added: “The next morning, once the instruments were installed, this route was uploaded to the rover. It then began its first exploration, with some debugging and manual interventions needed along the way.

“Nevertheless, after a long working day that lasted until sunset, the data collected by the instruments were sent back to the control centre.”

For some years, Bridget has been helping Astrium study a number of engineering solutions in preparation for ESA’s ExoMars mission. She was used extensively for the development and testing of the locomotion, suspension and steering systems and was then reconfigured to incorporate flight performance stereo cameras and an autonomous navigation system.

The final ExoMars rover that results from all the testing will be far more autonomous than current rovers, able to move faster and select its own route to the next point of interest, making best use of the terrain. This means that, once given the next ‘target’, the rover can make its own way there, with no further control commands. This feature is particularly useful when signals or commands from Earth can, in the worst case, take up to 20 minutes to get to Mars!

To navigate and steer, Bridget relies on stereoscopic cameras at the top of a two-metre mast, which allow her to see in 3D in much the same way as we do. An elevation model of the terrain is created from the images and fed into the navigation computer.

The six independently driven wheels are entirely of metal but have been engineered to behave like normal tyres, and the suspension system is designed to be able to negotiate all sorts of tricky slopes.

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