By Jonathan Amos and Paul Rincon
Science reporters, BBC News
The European Space Agency (Esa) is pushing forward with its design for a rover mission to send to Mars in 2013.
The robot rover would search for past or present life on the planet
Project teams have been authorised to investigate a concept that would launch a 205kg robot on a heavy-lift rocket.
The vehicle, expected to land in September 2014, would be equipped with a 16.5kg package of instruments to search for past or present life.
The concept is bigger - and much more expensive - than the one originally approved by space ministers in 2005.
The project teams will now refine the concept over the coming months, providing a detailed costing that Esa delegations can then approve or reject later in the year.
The delegations from the member states met with agency officials in Paris on Monday to agree the next development phase.
"We had a lengthy detailed discussion on various aspects of the ExoMars mission," said Bruno Gardini, a member of Esa's ExoMars project team.
"In the end, the delegations gave us the authorisation to go-ahead with industrial activity on the basis of this new technical baseline," he told BBC News.
For months, scientific and industrial groups across Europe have been developing a number of concepts in parallel.
ENHANCED EXOMARS CONCEPT
Would leave Earth in 2013; primary aim is to search for life
Could use a heavy-lift Proton or Ariane 5 rocket
Vented landing bags allow for a larger payload
Rover would carry a 16.5kg 'Pasteur' instrument suite
A geophysics/environment static station also possible
This would study the weather and listen for 'Marsquakes'
Extra cost requires Esa states to release more funds
The original 650m-euro "baseline option" involved launching the rover on a Russian Soyuz rocket, and without the stand alone "weather station" (or Geophysics/Environment Package - GEP) that many scientists wanted to take to the Red Planet.
The new configuration agreed at this week's Programme Board for Human Spaceflight, Microgravity and Exploration is the so-called "extended baseline option".
It consists of a 205kg vehicle, carrying a 16.5kg package of science instruments - and it incorporates a 30kg GEP.
The concept calls for a special type of landing technology that uses a vented airbag, and requires all the elements be launched on a more powerful rocket, such as an Ariane 5 or a Proton.
What will not be part of the mission, it seems, is a dedicated orbiting spacecraft to relay data from the Martian surface.
Instead, the ExoMars rover will rely on US orbiters already circling the Red Planet for communications with Earth.
This solution has previously caused disquiet in some quarters: if the US were to experience a spacecraft failure - as happened last year - ExoMars could be compromised.
The enhanced baseline would send ExoMars on a carrier platform that could enter a "parking orbit" around the planet.
"Rather than going for a direct injection - in which you get what you get - here you can study the atmosphere from orbit and when you think all the conditions are right, only then do you release," said Jorge Vago, ExoMars project scientist.
This should enable the rover to sit out the Martian dust storm season from the safety of space. It will also allow controllers to improve the accuracy of their landing.
Esa has also been exploring collaboration with the Russian federal space agency (Roskosmos).
Russian scientists are already involved on some of the instrument teams, but Esa has been discussing whether Russia would provide a Proton rocket launcher as an in-kind payment.
What the Russians would be offered in exchange, however, is still unclear.
"Right now we are trying to make our Christmas lists on both sides and see to what extent we can make one another happy," said Dr Vago.
EADS-Astrium has been developing the rover's chassis at its UK base in Stevenage. It has built a testbed to examine the vehicle's locomotive capability, and to try out the autonomous navigation software that will eventually guide ExoMars over the Red Planet's rock-strewn landscape.
The company's ExoMars group leader, Mark Roe, said the decision to move forward with the heavy-lift concept was very good news.
"We now need to take half a step back to confirm the configuration we have is the right one. It will almost certainly be six wheels but the detailed arrangement of the bogey is something that needs to be investigated," he told the BBC.
"We still have a lot of work to do in packaging the vehicle around the preferred payload concept, and to sort out the comms side - how we communicate through the mission."
At the Programme Board meeting, delegations authorised Esa to release what is known as a "request for quotation" from industry by mid-July.
The industrial partners answer this with their technical and financial proposal for the mission.
Based on the price that industry provides, the space agency will then go to delegates to give them a detailed estimate of the extra cost of the enhanced baseline.
This will range from, at the very least, tens of millions euros to perhaps even a few hundred million euros.
A meeting will take place in November to discuss the financial details - to decide if the mission is still affordable.
Last week, the project's prime industrial partner, Thales Alenia Space, announced the successful first test of the vented, or dead-beat, airbag technology that could be used to cushion ExoMars' landing.