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81 Space systems | Insight to take up less than 20 s on the image coprocessor to produce the model from the stereo navigation images. The C code has been cross-compiled for the LEON2 processor on the Pender board, and wrapped in test harness code that runs on the RTEMS operating system. This test harness code allows the execution speed of the algorithms to be evaluated on the Pender board for given stereo pair inputs and configuration parameters The coprocessor’s output is delivered to the rover’s main processor, which is another LEON2. This main processor then provides the position or velocity data for the actuators on the wheels, and this data is sent to the actuation drive (AD) electronics. The AD electronics are deliberately mounted outside the rover, to reduce the number of cables between it and the motors driving the wheels. This reduces the cables coming out of the rover, and so reduces heat loss. “Every cable coming out of the rover’s warm body is a thermal leak, so if you minimise the number of cables you minimise the leaks,” Joudrier explains. “Warming up electronics is something we can do, but we also need to warm up the motors as well.” The rover is steered using all six wheels, and can steer and drive at the same time as a result of the separate image coprocessing module to provide the navigation data. Joudrier says, “We are working to a critical design review at the moment, and all the subsystems are being procured by contractors. Once these have reached that level, there will be the system critical design review, probably towards the end of this year or the beginning of 2016.” NASA is also planning to go back to Mars with a new rover in 2020, but based on the existing chassis on the Curiosity vehicle and updated versions of the existing equipment. All the scientific instruments have been selected, including a new camera, Mastcam-Z, from Malin Space Science Systems (MSSS), which will also provide uplink planning services during mission operations. Mastcam-Z is derived from the Mastcam cameras operating on Curiosity, and it will have a stereo 3.6:1 zoom optical system (28-100 mm) to allow imaging over a broad range of fields of view. It will use the same image sensor as the Curiosity Mastcam but will fill the complete 1600 x 1200 pixel sensor area.  “We wanted to take advantage of all the work we did for our Mastcams, while addressing some of the limitations,” says Mike Ravine, advanced projects manager at MSSS. “We felt that the most cost-effective improvement was to add a zoom to provide better stereo capability. It will deliver the same optical quality as the fixed focal-length systems, while giving the flexibility to trade resolution against coverage and data volume.” Conclusion While it may seem that the design of autonomous systems is largely terrestrial, lessons are being learnt from space system designs. The complex interaction between the mechanical and electronic elements in them is highlighted by the severe constraints on available energy in space, bringing innovative solutions to problems on Earth. Unmanned Systems Technology | Summer 2015 The separate image processing subsystem for the ExoMars rover allows simultaneous steering and driving for the first time Every cable that comes out of the rover’s body is a thermal leak, so if you minimise the number of cables you minimise the number of leaks