The $100bn ISS has been blighted by toilet trouble

The main toilet has broken down on the International Space Station (ISS), currently home to a record 13 astronauts, Nasa said.

Mission Control told the crew to hang an "out of service" sign until the toilet can be fixed.

The crew of the shuttle Endeavour is confined to using the craft's loo. ISS residents are using a back-up toilet in the Russian part of the station.

If repairs fail, Apollo-era urine collection bags are on hand, Nasa said.

"We don't yet know the extent of the problem," flight director Brian Smith told reporters, adding that the toilet troubles were "not going to be an issue" for now.

Bad plumbing?

The main toilet, a multi-million-dollar Russian-built unit, was flown up and installed on the US side of the space station last year.

It had broken down once before, requiring a rush delivery of a replacement pump by the shuttle Discovery in 2008.

And another toilet-related row broke out earlier this year, when a Russian cosmonaut complained that he was no longer allowed to use the US toilet because of billing and cost issues.

Despite the latest housekeeping setback, astronauts managed to transfer spare parts from the shuttle Endeavour to the ISS on Sunday, the second day of a planned 11-day mission.

Nasa was also investigating why Endeavour's tank shed an unusually large amount of insulating foam during its launch.