US and European efforts to send joint missions to Mars have encountered yet another hitch.
A letter from Washington formally committing to combined ventures at the planet this decade was expected in Paris this week, but has not arrived.
It makes it harder for Europe to authorise its industry to start the next phase of building on an orbiter to hunt for Methane in Mars' atmosphere.
Industry has warned that time is running short to complete construction.
The delay in giving the commitment is understood to relate to the US space agency's (Nasa) difficulty in organising its finances for the multi-billion-dollar ventures, which also includes a big rover to search for traces of life - past or present.
Member states of the European Space Agency (Esa) want the assurance that the Americans will keep their side of the bargain, particularly on the rover, before they write a cheque to industry to start cutting metal on flight hardware.
Esa's Industrial Policy Committee was this week supposed to release industry to begin that work, but discussions on the matter will now take a different shape at the IPC's current meeting because the letter from Nasa has failed to materialise.
Known in Europe as the ExoMars project, the joint venture between the agencies comprises two separate missions.
The first, in 2016, is an orbiter to track down the sources of methane and other trace gases recently detected in Mars' atmosphere. The presence of methane is intriguing because its likely origin is either present-day life or geological activity.
Confirmation of either would be a major discovery.
In 2018, the agencies then plan to send their large rover to the Red Planet - perhaps targeted at one of the most interesting sources of methane to investigate further.
The 2016 satellite would act as the surface vehicle's data-relay station to get its pictures and other information back to Earth.
Industry says the timetable for construction, particularly for the orbiter, is tight if launch dates are to be met; and that it cannot wait much longer to start fabrication of key components.
"We are already compressing the uncompressible", was how one industry official described the situation to the BBC at last week's Paris Air Show.
For followers of European space affairs, the ExoMars initiative has been a long, drawn-out affair. It was originally approved as a concept by ministers in 2005, but then went through several iterations as scientists and engineers struggled to match their ambitions for the project to the funds available.
A decision to combine efforts with the Americans was taken when they too encountered budget pressures on their Mars Programme.