Astrium’s Mars Rover engineering development model

Bridget was designed and developed by Astrium in the UK to study a number of engineering solutions in preparation for the European Space Agency’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.

Autonomy

Through the development work carried out on Bridget, the follow-on ExoMars rover 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!

Navigation

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. Future rovers will also have an extra pair of cameras at the base of the mast which are used for visual localisation.

Wheels and suspension

Bridget has six wheels which are made entirely of metal since rubber is an organic material and therefore cannot be taken to another planet, particularly when searching for signs of life. The wheels have been engineered to behave like normal tyres, and the suspension system is designed to be able to negotiate slopes both parallel and perpendicular to the direction of travel.

Steering and wheel walking

All six of Bridget’s wheels are driven by independent electric motors controlled by the central computer, but only the four corner wheels are steered. In all the follow-on vehicles all six wheels are steered and a powered hinge above each wheel, used initially to deploy the wheel from its in-flight stowage position, will allow ‘wheel walking’ where each wheel can be rolled forward one, two or three at a time to avoid sinking in the softest of sand or dust.

The future

Though Bridget has handed over most of the development work to her ‘sons’ Bradley and especially Bruno, the latest prototype, she is often brought out of retirement to provide a realistic test platform for the many instruments, cameras and computers that are being prepared for ExoMars and future robotic missions. Unlike Bridget, Bradley and Bruno are restricted in the equipment they can carry as their wheels and suspension are designed for operation on Mars itself where gravity is 1/3 that of Earth.

Bridget’s vital statistics:

Bridget’s brother Bruno

Bruno Bruno is central to the development of autonomous navigation which will enable the rover to ‘drive itself’ across the surface of Mars, without constant commands from Earth.