WASHINGTON — Orbital Sciences Corp. beat out several other finalists to win a NASA Space Act Agreement award worth $171 million to build and demonstrate a launch system capable of delivering cargo to the international space station.

NASA made the award under its $500 million Commercial Orbital Transportation Services (COTS) program, which is aimed at stimulating privately owned alternatives to the space shuttle and other government systems for ferrying crew and cargo to the space station.

The U.S. space agency intends to hold an open competition in the years ahead for actual space station cargo-delivery contracts, but Orbital of Dulles, Va., is one of two companies receiving financial help from NASA to develop their proposed systems. The other is Space Exploration Technologies of El Segundo, Calif.

The $171 million NASA awarded Orbital Feb. 19 became available last fall after the agency ended its COTS agreement with Rocketplane Kistler when the latter was unable to raise the $500 million in private financing it needed to finish its K-1 reusable rocket. Rocketplane Kistler of Oklahoma City and Space Exploration Technologies were the original COTS awardees.

NASA currently depends on the space shuttle and Russian Progress spacecraft to deliver supplies to the space station. After the space shuttle retires in 2010, the space station will be dependent on European, Japanese and Russian spacecraft for logistics until NASA's Orion Crew Exploration Vehicle or a U.S. commercial alternative enters service.

With Orion not scheduled to make its debut until March 2015 and no guarantee that the U.S. private sector will succeed in fielding a commercial alternative, NASA Administrator Mike Griffin asked Congress Feb. 13 for legislation this year to permit the agency to place a new order with Russia later this year for additional Progress unmanned supply ships and Soyuz crew capsules.

NASA already has agreed to buy roughly $700 million worth of such services from Russia through 2011, when a temporary congressional waiver of the Iran-North Korea-Syria Non-proliferation Act is due to expire. The law prevents NASA from buying space station-related goods and services from Russia as long as that country's aerospace sector continues to help Iran acquire missiles and other advanced weapons.