CAPE CANAVERAL (USA), Aug 30: The United States begins its next step in human space flight with the announcement by Nasa on Thursday of a contractor to design and build spaceships to fly to the moon.

Lockheed Martin Corp and a partnership of Northrop Grumman Corp. and Boeing Co are vying for the work, estimated to be worth more than $18 billion over the next decade.

“We’re looking forward to getting that contractor on board with us as we continue our journey on into exploration,” project manager Skip Hatfield said.

The new spaceships, named Orion, will replace the US space agency’s three remaining space shuttles, which are to be retired in 2010 upon completion of the half-built International Space Station.

After two deadly shuttle accidents, Nasa is giving up on winged, reusable vehicles and returning to the capsule-style spaceships that first carried Americans into orbit and later landed them on the moon. Similar vessels are used by Russia and China.

The contract, to be announced at a news conference in Washington, covers the design, development, production and testing of engineering models and up to four operational vehicles.

The spaceships are slated for test flights within six to eight years. Two versions are planned, one to carry astronauts, the other for cargo.

Initially, Orion spacecraft will fly to the space station, supplementing the Russian Soyuz spacecraft as emergency escape ships and ferrying crews to and from the outpost.

By 2020, Nasa intends to fly astronauts to the moon for the first time since the final Apollo mission in 1972, an effort expected to cost more than $100 billion. After building an outpost on the moon, the plan is to send astronauts to explore Mars.

The programme, called Project Constellation, shifts US human spaceflight beyond research and satellite-delivery missions in low-Earth orbit carried out by the shuttles.

It was implemented in the wake of the 2003 shuttle Columbia disaster and in response to sharply worded advice from accident investigators calling for recertification of the remaining space shuttles.

Few questioned President George W. Bush’s decision to end the shuttle programme. Even die-hard Mars exploration enthusiasts eventually stopped complaining about being waylaid by precursor lunar excursions.

But critics and government advisers have raised questions, particularly over the multibillion award to build spaceships before technical and financial risks are fully understood.—Reuters