A Russian Soyuz TMA-18 rocket is seen in preparation for launch at Kazakhstan's Russian-leased Baikonur cosmodrome on April 2, to the International Space Station (ISS). NASA announced Tuesday that it signed a contract with the Russian space agency to shuttle US astronauts to the orbiting International Space Station.

NASA announced Tuesday that it signed a contract with the Russian space agency to shuttle US astronauts to the orbiting International Space Station.

The 335 million dollar contract extension is for the "transportation, rescue and related services" of US crew bound for the ISS in 2013, NASA said in a statement.

The contract "covers comprehensive Soyuz support, including all necessary training and preparation for launch, crew rescue, and landing of a long-duration mission for six individual station crew members."

US astronauts bound for the ISS will depart aboard four Soyuz missions in 2013, and will return to Earth aboard two Soyuz missions scheduled for 2013 and two in 2014.

The United States is due to retire its aging shuttle fleet this year, and from then on will depend on Russian Soyuz flights to transport its astronauts to the ISS until the Ares 1 rocket and its Orion capsule are operational in 2015.

President Barack Obama's administration in February proposed scrapping the costly and over budget Constellation rocket program, designed to send Americans to the moon by 2020.

The US space shuttle Discovery blasted off Monday toward the ISS, the fourth last mission for the shuttle program before all three remaining US manned orbiters are retired at the end of 2010, ending 30 years of service. The first shuttle flew in April 1981.

The International Space Station, a 100-billion-dollar project begun in 1998 with the participation of 16 countries, is financed mainly by the United States.

Explore further NASA green lights April 5 launch of Discovery

(c) 2010 AFP