As relations between the United States and Russia plummet over the latter's annexation of the Crimean peninsula, one of the unintended victims could be the International Space Station, where Russian cosmonauts and American astronauts currently share very close quarters, some 400 kilometers above the earth.

With a Russian Soyuz spacecraft due to blast off for the space station this week carrying one American and two Russians to join the Russian, American and Japanese astronauts who are already there - officials from both countries are downplaying the potential problems.

"We are confident that our two space agencies will continue to work closely, as they have throughout various ups and downs of the broader U.S.-Russia relationship," the National Aeronautics and Space Administration NASA said last week, in a statement quoted by Discovery News.

Nevertheless, concerns exist. The Pentagon last week instructed the U.S. Air Force to conduct a review of its use of the Russian-made RD-180 motor in the Atlas V rockets, which propel military satellites into space, in case Russia were to cut off supplies.

The retirement of the U.S. space shuttle program in 2011 left Americans without a vehicle for ferrying crew to low-earth orbit, and a commercial replacement is not expected to be up and running before 2017.

The U.S. needs Russia to transport astronauts to the space station, and currently pays an average of $70.7 million per seat, according to a NASA spokesman. Reliance on Russia's Soyuz spacecraft is a key reason why the United States cannot break off space ties.

"It is always in Russia's capability to cut off their service," said John Logsdon, a member of the NASA Advisory Council, estimating the likelihood of such an action at 20-25 percent. "It would be a catastrophe. There is mutual dependence and that provides a good motivation to isolate this from the broader issues."

American astronaut Mike Hopkins, who returned from the ISS earlier this month after a half-year stay, said he considered his Russian counterparts "close friends" and described cooperation as "very strong." Space officials from both countries seem to be counting on those personal bonds enduring.

Representatives from Russia, the U.S., Canada, Japan and Europe have lived continuously aboard the space station in rotating crews for more than 13 years, and the life of the station was recently extended to 2024.

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Will U.S.-Russia tensions extend into space?