BBC Science Correspondent Susan Watts: Has Nasa lost the plot?

Nasa astronaut Bill Shepherd told BBC Television's Newsnight programme that this would be a "big mistake".

He pleaded for patience with Russia, which is experiencing problems building the service module - containing living quarters for the crew - because of its economic crisis.

His criticism came hard of the heels of the space agency's moment of glory - the relaunch of the world's oldest astronaut, John Glenn, into space on Thursday.

Spirit of co-operation

Mr Shepherd - who will be the first commander of the space station - said that co-operation with Russia was an essential part of the project.

Shepherd speaks out

"I know Nasa is developing plans to make the space station happen without [the Russian module], but it's a signature piece of our team's spirit of co-operation, and if we don't have this it's going to be substantially weaker." he said.

He added: "If there is a way to assemble the station in the correct order and we can wait for the service module then my instinct is let's wait."

BBC Science Correspondent Susan Watts says it is doubtful whether the module - which is due to be ready by next April - will ever be completed. It forms the third part of the basic structure of the station.

Units will be fixed together in space

The first two modules - the Russian Zarya and the American Unity - are to be launched on 24 November and 3 December respectively.

But without the service module, the crew will not be able to go into space.

According to Mr Shepherd, Nasa is toying with two uncomfortable options: launching the station without a service module to begin with, or building its own model, cutting out the Russian contribution.

"I think we will get to a decision point late spring where if it looks like the service module is not going to happen, we will start to assemble other pieces without it," he said.