By Jonathan Amos
Science reporter, BBC News
Demonstrators are a vital step before building the real thing
The wheels continue to turn on Europe's billion-euro project to put a robotic rover on the surface of the Red Planet.
Engineers working towards the flagship ExoMars mission have unveiled a sophisticated new vehicle prototype.
The demonstrator will test a possible suspension and locomotion set-up to be built into the final rover design.
ExoMars, which has yet to receive final sign-off from space ministers, is scheduled to leave Earth in 2013 and land on the fourth planet a year later.
It will carry a suite of instruments across the Martian landscape, looking for signs of past or present life.
The new prototype, developed by the Canadian MDA Corporation, will help engineers understand how the real rover will behave when it moves through the rocky terrain.
"This will be the first element that touches the surface of Mars as ExoMars rolls off the lander," explains Nadeem Ghafoor, MDA's manager of planetary exploration.
"And when you've decided where you want to go, this is the system that gets you there and gets you over any obstacles on the way," he told BBC News.
Moving on Mars
The MDA prototype can be viewed much like a car without its body. What you see in these pictures from a recent test session is essentially an undercarriage. The boxes on top house the current avionics needed to run the rover systems.
On the eventual flight vehicle, such boxes would be joined by other computers, antennas, solar panels, cameras and the all important instrument suite which would run the exobiology experiments.
EXOMARS MISSION CONCEPT
Set to leave Earth in 2013; primary aim is to search for life
Will launch on a heavy-lift rocket, such as the Ariane 5
Vented landing bags allow for a larger payload
Rover will carry a 16.5kg 'Pasteur' instrument suite
30kg geophysics/environment static station also possible
This would study the weather and listen for 'Marsquakes'
Concept to cost Esa states more than first estimates
MDA was given a list of requirements to work to. These concerned issues of stability; the type of terrain and soil the vehicle would have to traverse; obstacle heights; mass and power parameters.
The company's engineers were then left to come up with what they thought were the most appropriate solutions.
They investigated six major suspension configurations before deciding on a rigid bogie, or trolley, system that incorporates six driving and steering wheels.
"Each wheel can turn which allows us to do point turns, rotating about the centre of the rover chassis," said MDA's ExoMars project manager, Mike Schmidt.
"It can do a regular turn like you would do in your car, going around a sweeping bend. And it also allows us what's called crab mode, in which all six wheels turn in the same direction, allowing the vehicle to shuffle sideways like a crab would.
"This provides benefit if you want to get up close to an object to deploy scientific instruments."
The vehicle can also extend its wheel base to alter its pose or stance. This allows it to lean one way or another.
"This will help with stability [on slopes] but also in the deployment of certain instruments or drills that need a certain orientation with respect to the surface," said Mr Schmidt.
The MDA set-up is built from aluminium and stainless steel. The final rover, though, would probably incorporate titanium and a beryllium alloy to reduce the weight of the system.
Even so, the current one-and-a-half-metre-long MDA mechanism is only 76kg.
The flight vehicle which goes to Mars will be about 200kg, all systems included, and have to fold up into an extremely tight volume for transport to the Red Planet.
ExoMars needs a final sign-off from ministers
MDA's investigations are being run in parallel with those of a Swiss-German consortium, led by the Oerlikon and VH&S companies, which has produced its own prototype.
Overseeing the whole process of chassis development is the UK arm of EADS Astrium.
In about June, the British outfit will call in both machines, which are said to share broadly the same technical solutions.
Astrium intends to load both with navigation software and hardware and make them run around a "Mars yard", a test facility set up to simulate the Red Planet's landscape.
Later this summer, just one of the teams will be asked to take the design forward.
"At the same time as completing this work, the teams put together bids in response to invitations to tender. We've received those tenders and are currently in the process of evaluating the best one," explained Astrium's ExoMars industrial manager, Chris Draper.
"On the basis of that, one or the other will be selected for flight implementation. The next phase will be to qualify the design, to build engineering and qualification models that undergo all sorts of environmental tests - being shaken, and heated up and down, etc."
The ExoMars project has grown in scope down the years.
Member-state delegations to the European Space Agency (Esa) initially approved a 650m-euro programme in 2005, since when design reviews have indicated that a better value science return would be achieved through a bigger, more capable rover.
However the cost for this "enhanced baseline" - of the order of a billion-plus euros - will have to be cleared again by space ministers when they meet in The Hague in November.
Although clearly not in Europe, Canada has special co-operative status within Esa and, as such, the country's space agency and companies are regular participants in Esa projects.
MDA, as one of the world's leading space robotics firms, is well paced to assist in the ExoMars effort.
The company is perhaps best known for providing the space station's robotic arm system, Canadarm2, and its recently installed extension, the Dextre two-armed manipulator.
"It's a really exciting time here and it would be great to take that expertise and all that technology and put it into the locomotion system on the ExoMars rover," said Nadeem Ghafoor.