Field trials in what may be Earth’s most Mars-like terrain have flagged up some of the challenges that the European Space Agency scientists will face when their 2018 ExoMars mission puts a rover on the Red Planet – and software being developed for the project may also help develop fully autonomous robots that drive or fly here at home.
The trial, to simulate six days on Mars, involved sending an Astrium-built rover named Bridget to the Atacama desert in Chile and controlling it from the Satellite Applications Catapult facility at the UK’s Rutherford Appleton Laboratory at Harwell, near Oxford.
The rover was looked after by a local team, but all instructions came from controllers back at Harwell who knew nothing of the desert terrain except what they could glean from the rover’s stereo camera and ground-penetrating radar (to look for suitable spots to deploy the ExoMars rover’s 2m drill), and satellite images degraded to the 30cm resolution available from Mars orbiters.
As Astrium’s Lester Waugh puts it as the event kicked off, field trials are always valuable because they turn up unexpected difficulties, ranging from technical problems to shortcomings in teamwork. In addition, he stressed, shaking out problems now is critically important; every minute on Mars is hugely valuable.
Thus, it is absolutely critical that Bridget’s successor be able to navigate autonomously. There is no GPS on Mars, where communication will be routed via an orbiter that has just one or two short windows daily to pass signals to and from the rover. And, even at the speed of light, radio signals take tens of minutes to reach Mars – so there is no prospect of safely driving the rover from Earth except in painfully short steps that would severely limit its range during a mission with a seven-month design life.
Hence, without discounting the importance of the rover hardware and getting it safely to Mars and down to the surface, the success of the mission is – to a great degree – a software problem. Mark Woods of software house SCISYS is leading that effort and describes the challenge as learning to “immerse yourself in a world that’s presented very differently than when you’re on the ground”.
The Mars rover will be given destination objectives and be expected to find its own way. To do that, it will use its onboard stereo camera to build a 3D map, and pick its way along, avoiding obstacles. Over distances of about 1km, says Woods, the rover will be on its own. At such intervals, though, it will be able to compare its own map to the 3D maps being built up by multiple orbiter passes and correct its course – for example to make up for wheel slippage in the Martian sand.
Woods describes the navigation system – a camera and small computer – as having the virtues of being cheap, simple and low powered. As the rover will not move quickly, and Mars is a static environment, that system seemed ideal for the space mission but not very useful on Earth. Google’s self-driving cars, he notes, rely on extra equipment such as radar, which lets them cope with fast-moving traffic, but would be too heavy and power-hungry for ExoMars.
However, simple also means reliable and, hopefully, future-proof. The hardware is fixed months before launch, but software updates can be sent to Mars. Woods wants, for example, to eventually give the rover enough “intelligence” to identify – autonomously – targets for scientific investigation. To wait for Earth-based analysis of the vast quantity of data that will be coming back will, inevitably, mean driving past spots that warrant investigation. That capability may not be ready in time for launch, but – especially if the rover exceeds its design life – it should be possible to enhance its usefulness.
The same future-proof design principle may apply to robotic systems such as unmanned aircraft, though the hardware is easily accessible for upgrade and repair. Indeed, what has surprised Woods about this project, is that potential customers here at home are thinking along just those lines: “I didn’t think that low-power and cheap would be important on Earth, but I’m finding it is.”
Source: Flight International