NASA postpones launch of space shuttle Endeavour

CAPE CANAVERAL, Florida (Reuters) - NASA cancelled plans to launch space shuttle Endeavour on a construction mission to the International Space Station on Saturday when sensors detected a hydrogen leak.

The leak was found as technicians neared completion of the loading of 500,000 gallons (1.9 million litres) of liquid hydrogen and liquid oxygen into the shuttle's fuel tank for a launch attempt at 7:17 a.m. EDT (12:17 a.m. British time), said Kennedy Space Centre spokesman Allard Beutel.

The problem is similar to a hydrogen leak that occurred while shuttle Discovery was being prepared for launch in March. NASA discovered a problem with a line that vents gaseous hydrogen from the shuttle's fuel tank.

Technicians replaced the faulty equipment and the shuttle was successfully launched four days later.

It was not immediately clear when the U.S. space agency might make another attempt to launch Endeavour.

NASA has said it will only allow three days for launch attempts of the shuttle before delaying to July so that a previously scheduled unmanned moon probe can be launched.

Both the shuttle and the Lunar Reconnaissance Orbiter's Atlas rocket use safety and support services from Cape Canaveral Air Force Station, which needs two days to configure equipment for different launch vehicles. LRO is slated to fly on Wednesday.

The moon probe is NASA's debut mission in a new exploration initiative aimed at returning astronauts to the moon in 2020.

NEW ATTEMPT

NASA managers planned to meet later on Saturday to assess when to make another attempt to launch the shuttle.

Endeavour is carrying a Japanese-built porch that will be installed on the station's $2.4 billion Kibo complex, Japan's primary contribution to the $100 billion station program.

The lab includes a robot arm and a small airlock so science experiments can be installed outside the station and retrieved without the need for spacewalks by station or shuttle crew members.

Endeavour also is carrying laboratory racks, experiments, supplies and dozens of spare parts, which will be stored aboard the outpost in preparation for when the shuttle is no longer flying.

NASA has eight shuttle missions remaining to complete construction of the station. It plans to retire the three-ship fleet at the end of 2010.

The Endeavour crew plans to spend 12 days at the station and conduct five spacewalks to install the porch, replace batteries and tackle a long list of maintenance tasks.

The mission is NASA's first since the station's live-aboard crew was expanded to six members from three last month.

When the shuttle crew arrives, it will bring the total number of people aboard the space station to a record 13.

The combined crew includes two Canadian astronauts -- station flight engineer Robert Thirsk and Endeavour astronaut Julie Payette -- Japan's Koichi Wakata, Europe's Frank De Winne, Russian cosmonauts Gennady Padalka and Roman Romanenko and seven U.S. astronauts.

Wakata will be returning home with the shuttle crew after a three-month stay on the station. His replacement is NASA astronaut Timothy Kopra, one of Endeavour's four rookie fliers.

(Editing by Jim Loney and Sandra Maler)