We're going to extend two days, pending Russian concurrence

Mission Control

US space agency Nasa decided to extend the shuttle's mission because it is providing a vital communications link with the station's crew of three astronauts.

The shuttle had been due to leave the space station on Saturday and return to Earth; the plan now is to keep them docked together until Monday and hope the computers can be repaired by then.

Millionaire Mr Tito had been due to take off from Russia on Saturday, but because of the changes, Nasa has contacted the Russian space agency to set a new day for the launch.

Software blamed

Astronauts onboard the ISS hope to perform some tricky manoeuvres on Friday after one of its computers came back online following a serious failure.

These include moving the station's newly installed 58-foot (17 metre) robot arm, and firing the space shuttle Endeavour's engines for an hour to raise the station into a higher orbit.

However, Mission Control wants at least two of the ISS' computers to be fully functional before attempting either operation.

Those on board the station were not in danger

Technicians worked through the night to restore control over the orbiting platform after losing contact with its payload computer system, a backup and a standby on Wednesday.

During the computer failure, Nasa used systems on board Endeavour to communicate with the ISS. It could also have talked to the station via Russian ground controllers.

The use of rotating main, backup and standby systems is designed to prevent such a communications breakdown, but, it seems, all three systems were cut off at the same time.

Flight controllers will analyse its systems to try to find out what went wrong, Nasa said.

Space tourist

The agency believes software problems were probably to blame for the outage, it said.

Endeavour had been scheduled to depart on Saturday, about six hours after Mr Tito was to lift-off in a Soyuz space capsule.

Mr Tito, 60, was originally schedule to blast off on Saturday from Kazakhstan's Baikonur space centre after Nasa and its partners in the ISS project granted an exemption on Tuesday to allow him aboard the station.

Mr Tito is paying $20m to travel to the ISS on board a Russian Soyuz rocket.