Europe's Mars rover traverses a rocky road
It's pretty clear now that , Europe's flagship robotic mission of the next decade, is going to be pushed back again. It's .
Originally conceived as a small technology demonstration venture, and should have left Earth in 2011.
But then, as so often happens with space missions, the complications began. , and so did the budget.
Designers started to put more instruments on the proposed mission and the whole concept got heavier. Before long, the relatively inexpensive Soyuz launch rocket planned for ExoMars was being pushed aside for a bigger and considerably more costly booster - an Ariane 5 or a Proton.
Ministers naturally got anxious, and as everyone tried to pull together something coherent and affordable.
The budget for ExoMars has been . The concept that scientists and engineers had wanted to launch cannot be done for that kind of money. They need something more in the region of 1.5bn.
The solution has been to join forces with the Americans, to essentially merge the Red Planet exploration goals - and budgets - of Esa and Nasa.
This suits the Americans because they too have money woes. Their next big rover - the (recently re-named "Curiosity") - is also way over-budget and late.
When the chief scientists of Esa and Nasa - David Southwood and Ed Weiler - in Plymouth, UK, they christened this new union the .
It covers the launch opportunities to Mars in 2016, 2018 and 2020 (launch opportunities to Mars come up roughly every two years when the orbits of Earth and the Red Planet are most favourably aligned).
My colleague Paul Rincon and I have written about what could go when: .
Moving ExoMars to 2018 is part of the mix, but getting everybody to swallow this is going to involve considerable negotiation.
As with many Esa missions, workshare is divided up according to a member state's investment in a programme. Italy and the UK are the two biggest investors in ExoMars, so their industries get the lion's share of the contracts.
The UK has been given the task, through EADS Astrium UK, of developing the rover itself - the six-wheeled truck that hauls the science instruments over the surface of Mars.
Italy, by virtue of its bigger investment (about 40% of the total budget), is actually the lead nation; and Thales Alenia Space in Turin is the prime contractor. Italy is the project's heart, its operations centre.
It's where the sterilised ExoMars would finally be bagged up and sent to the launch pad. Italy would also look after the machinery for getting the rover on to the Red Planet - the notoriously difficult business of (EDL).
And so here's the key stumbling block: under the MEJI marriage, Italy and Italian industry is being asked to step aside on EDL to allow the Americans to look after it.
Put another way just to emphasise the point: the lead nation on ExoMars is being asked to give up one of the key competencies on the mission.
As one senior Italian industry executive told me recently: "It's alright for the UK; they are largely unaffected. The changes hurt Italy much more."
France, too, as it would also be heavily involved in EDL.
Esa now finds itself in a difficult position. It wants to re-scope the mission into a wider programme of exploration with the Americans, but it is somewhat hamstrung by its rules on industrial workshare.
Officials have to persuade Italy that its role in ExoMars remains as central as ever, and that there is an opportunity elsewhere in the MEJI timeline for it to demonstrate EDL.
That opportunity is likely to be in 2016 when the Esa-Nasa partnership could send an orbiter to search for the . This proposal has space, as part of the mission, for a small lander to be put down on the surface of the planet.
The ExoMars story rolls on. Watch this space.
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