WASHINGTON -- The chill left on US-Russian relations by Moscow's military incursion into Georgia could spell problems for future US access to the International Space Station, US experts said.

The National Aeronautics and Space Administration will become dependent on flights to the ISS by Russia's Soyuz spacecraft when it retires the shuttle fleet that has long ferried US astronauts into space in 2010.

NASA will only get its successor space vehicle, Orion, planned for a revival of trips to the moon, ready for flight in 2015 at the earliest.

That leaves the needs of US astronauts visiting the ISS vulnerable to the possibility of a new Cold War between Washington and Moscow after Russia's powerful military overran much of Georgia two weeks ago in the dispute over South Ossetia.

"If recent Russian actions are any indicator, a technical excuse to completely block US access to the ISS for geopolitical reasons would fit nicely into the Kremlin toolkit," Vincent Sabathier, an expert on human space exploration at the Center for Strategic and International Studies in Washington, told AFP.

Sabathier noted that not only was the short Georgia war a serious thorn in relations, but also the US determination to set up in Poland and the Czech Republic its missile defense system, which Russia calls a threat to its military.

"Almost immediately after the Czech Republic signed an agreement with the US to place missile defense tracking radar in its territory, oil supplies through the Druzhba pipeline to the central European country were reduced to a trickle... ostensibly for technical reasons," Sabathier said.

The end of the three-decade-old shuttle program leaves NASA with at least a five-year hole on which it will have to pay Russia's space agency to deliver and retrieve US astronauts and cargo to the ISS.

That depends as well on the US Congress voting an exemption to a 2000 law that bans US government agencies from opening contracts with countries like Russia that are considered aiding Iran and North Korea, which the US has labelled supporters of terrorism.

Even before the Georgia fighting erupted on August 8 there was opposition in the Congress to such an exemption, and now that has likely increased, according to Florida Democratic Senator Bill Nelson.

"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," Nelson said.

"Now, I'd say it's almost impossible."

Nelson, who supports allowing NASA to contract the Soyuz, said that without the exemption the US could find itself in 2011 with no access to the $100-billion space station -- largely paid for by the United States.

Because the ISS needs someone aboard all the time to keep it going, the situation, Nelson said, would mean leaving the station to "degrade and burn up on reentry, or with us ceding it to those who can get there."

NASA's chief Michael Griffin told AFP just days before the Georgia conflict erupted that it was a "great concern" that something could happen to make Soyuz unavailable.

"If anything at all in that five years period goes wrong with the Russian Soyuz, then we have no system to access the space station."

But after the Russia invasion of Georgia, NASA downplayed the political risk, saying it has a long history of cooperation with the Russian Federal Space Agency