Here's a scenario that might be going through the minds of NASA astronaut Greg Chamitoff and his two fellow Russian crew members on the International Space Station (ISS).

Lawmakers warned this week that escalating tensions with Russia may leave the U.S. without ready transport to the ISS after NASA retires the space shuttle fleet in 2010.

The space agency does not expect the shuttle's replacement, the Orion—an Apollo-like craft being developed as part of the Constellation program—to be ready to fly until 2015. NASA's plan was for the interim was to use Russian Soyuz craft (left) to send up crew and cargo to the $100 billion station.

U.S. Senator Bill Nelson (D.-FL) sounded the alarm on Tuesday that Russia's encroachment on contested Georgian territories jeopardizes that plan, which depends on Congress renewing a waiver to a 2000 law prohibiting American contracts with countries that have helped Iran or North Korea with their nuclear programs.

"In an election year, it was going to be very difficult to get that waiver to pay hundreds of millions of dollars to an increasingly aggressive Russia, where the prime minister is acting more and more like a czar," Nelson told the Washington Post. "Now, I'd say it's almost impossible."

Congress waived the law once already in 2005, allowing NASA to negotiate a $719 million contract with the Russians to use the Soyuz until 2011.

NASA is playing it cool. The space agency "has no reason to believe that it will be unable to rely upon Roscosmos-provided Soyuz vehicles for future ISS activities," spokesman Michael Curie told CNN.

Even if the waiver passes again, Nelson told Florida Today there's still the concern that with no competing service to space, Russia may end up "denying us rides or charging exorbitant amounts for them."

Then factor in the spotty performance record of the single-use Soyuz: it came down too steeply and landed well off target in an April return flight from the ISS carrying U.S. astronaut Peggy Whitson. NASA is working with Russian engineers to identify the cause of the problem and correct it.

So what's the backup plan? That's the problem, experts said: There isn't one. Getting Orion ready faster isn't in the cards. NASA this week confirmed a report leaked last month when it announced that flat budgets and technical problems would delay testing of Orion until late 2014.

Extending the shuttle program would require a change of course from lawmakers. The Post notes that NASA has already begun laying off shuttle staff and has stopped buying parts for the aging fleet.

Assuming diplomatic relations between U.S. and Russia do go south, might this be an opportunity for SpaceX, the commercial space delivery company founded by ex-PayPal billionaire Elon Musk? The company is developing rockets in two sizes to launch satellites and take cargo to the ISS.

The smaller Falcon 1 rocket failed its third test in a row two weeks ago. But it did successfully test fire the multi-engine first-stage of the larger Falcon 9.

Image credit: PD-USGov-NASA