By Irene Klotz
Cape Canaveral, Florida
The shuttle is entering its final days
Europe may have to find its own solutions for transporting astronauts and cargo to and from the International Space Station due to short-sighted US policies that now threaten Nasa's ability to maintain a presence on the orbital outpost.
Nasa chief Michael Griffin recently gave top managers a blunt assessment of the situation in an e-mail reprinted by the Orlando Sentinel, in which he said: "My own view is about as pessimistic as it is possible to be."
Fuelling Dr Griffin's frustration is a US policy to retire the space shuttle fleet in 2010, for safety and cost reasons, but five years before replacement ships are ready to take over the work of ferrying crews to the ISS.
The station also is solely dependent on Russia's Soyuz capsules to serve as lifeboats to bring astronauts back to Earth in case of an emergency.
The European Space Agency (Esa) had joined Nasa in designing a station crew-return vehicle based on the X-38 experimental craft, but it was never completed.
"That was cancelled by a US government decision when almost all the European components were ready or already delivered," Marco Caporicci, the head of the Esa's Future Space Transport and Infrastructure Division, wrote in an e-mail to BBC News.
That decision to depend on the Russians is squarely at odds with US policymakers who slapped a trade embargo on Russia after concerns of weapons proliferation to Iran and North Korea.
Nasa won an exemption to the ban to buy Soyuz rides and related technical support through to 2011. To keep the Soyuz manufacturing line flowing, a second exemption is needed by the beginning of the year.
With the recent Russian incursion into neighbouring Georgia, Dr Griffin said the exemption request was "DoA" (dead on arrival).
"The Russians are not going to back out of Georgia anytime soon, certainly not prior to the (US presidential) election," he wrote.
"We might get some relief somewhere well down the road, if and when tensions ease, but my guess is that there is going to be a lengthy period with no US crew on the ISS after 2011."
Esa's provision of the Columbus lab guarantees flights to the ISS
Nasa had asked for an additional $1bn a year to speed up development of the shuttle's replacement but was turned down.
The new capsules, which are being designed to travel to the Moon as well as the space station, are expected to debut in 2015.
The problem is not just Nasa's, though. The US promised transportation services to its European, Japanese and Canadian partners, which provided laboratories and other equipment for the space station.
Europe has a cargo hauler, the ATV, which made its debut flight this year. Caporicci said a proposal is being prepared for the Esa Ministerial Council for a cargo transportation capability that may be evolved to carry astronauts.
Esa is now thinking of upgrading the Ariane 5 rocket to carry a crew ship
"To achieve this second step, it will be necessary to analyse in detail the implications of adapting the Ariane 5 launcher and its ground segment to human spaceflight," Caporicci said.
"Any such decision would be coordinated with further improvements of the Ariane 5 launcher driven by the commercial missions.
"This successive step will be the subject of a dedicated decision by the Esa Member States at the occasion of the next Ministerial Council, once the programmatic framework will have been fully identified," he added in his e-mail.
Dr Griffin says he sees no political alternative, but for whomever is the next US president to decide to keep the shuttle flying. The question will be whether it is done at the expense of funding Orion, the shuttle replacement programme.
"This [White House] Administration will not yield with regard to continuing Shuttle operations past 2010, but the next Administration will have no investment in that decision. They will tell us to extend Shuttle.
"There is no other politically tenable course. It will appear irrational - heck, it will be irrational - to say that we've built a space station we cannot use, that we're throwing away a $100bn investment, when the cost of saving it is merely to continue flying Shuttle," Dr Griffin's e-mail said.
Mr Caporicci said he was confident Nasa and the US government would work out an option to keep the station operational. But just in case, Esa was working on "Plan B".
"We are evaluating developments for cargo transportation and return systems, based on our Ariane 5 and ATV," he said.
Any new system, however, still wouldn't be ready to fly until 2015 at the earliest, leaving a gap of four years.
Esa also was thinking about partnering with Russia for future crew transportation systems, Mr Caporicci said. "But that is essentially beyond the ISS, since they would not make their first flight before 2018."