Lawmakers have asked NASAs chief how the U.S. can maintain use of the International Space Station if Russia delivers on a threat to end its participation after 2020 as the crisis in Ukraine strains relations.

We will need to step back and evaluate the costs and benefits of maintaining the station without our Russian partners, House Science Committee Chairman Lamar Smith, a Texas Republican, and members of the panel said in a letter today to NASA Administrator Charles Bolden.

Russias Deputy Prime Minister Dmitry Rogozin said May 13 that his country would no longer export Russian engines for U.S. military rockets and also may withdraw from operations of the civilian space station. Rogozin was among Russian officials singled out for U.S. economic sanctions over his countrys takeover of Crimea from Ukraine.

Our international space partnerships, including our partnership with Russia, have historically endured political division, the lawmakers wrote. But Deputy Prime Minister Rogozins statements raise serious concerns about the strength of those partnerships.

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Since ending its manned space program in 2011, the National Aeronautics and Space Administration has depended on Russia to shuttle crews to and from the station that orbits 260 miles (418 kilometers) above the Earth.

Two U.S. companies, Orbital Sciences Corp. (ORB) and Elon Musks Space Exploration Technologies Corp., have NASA contracts to ferry supplies to the space station.

In addition, the government has contracts with SpaceX; Boeing Co. (BA); Sierra Nevada Corp.; and Blue Origin LLC, founded by Jeff Bezos, the chairman and chief executive officer of Amazon.com Inc., to develop a rocket and capsule capable of carrying astronauts to the station by 2017.

The lawmakers asked Bolden for information on international negotiations to keep the International Space Station functioning beyond 2020, and what the impact of a Russian withdrawal would be.

As we move forward, it is important that we fully understand our nations independent capabilities with regard to ISS operations, the lawmakers wrote.

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NASA Asked How to Keep Space Station Going Without Russia