Launch of space shuttle from Florida on hold

CAPE CANAVERAL, Fla, Sep 6 (Reuters) NASA today postponed the launch of the space shuttle Atlantis because of a problem with a power system aboard the ship, officials with the US space agency said.

The launch of Atlantis on NASA's first construction mission to the International Space Station since the 2003 Columbia accident had been planned for 2159 hrs ist (1629 GMT) today.

The next opportunity to fly would be at (2133 hrs ist) tomorrow Engineers detected a voltage spike in a power unit inside one of the shuttle's three onboard fuel cells. The problem was found shortly before the shuttle was to be loaded with a half-million gallons of propellants for launch.

The 250-pound units combine oxygen and hydrogen to produce electricity for the shuttle's systems and water that is used for cooling and for the crew to drink. All three must be operating for the shuttle to fly.

Preliminary analysis points to a glitch in a Freon cooling loop that is part of the system, said NASA spokeswoman June Malone.

''Any time you can isolate the problem, it helps you understand it better,'' she said.

NASA needs to resolve the problem quickly to take advantage of the two remaining days in the shuttle's launch window.

After Friday, NASA has agreed to delay the flight so that Russia can proceed with its launch of Soyuz spacecraft that will ferry a new crew to the outpost along with an Iranian-born American entrepreneur, Anousheh Ansari. She will fly home with the current station crew in a Soyuz capsule that is nearing the end of its orbital lifetime.

Fixing the power unit would be difficult while the shuttle is at the launch pad because the unit is hard to get to.

It is located beneath the liner of the payload bay near the crew cabin. That payload bay is filled with a double segment of the station's truss and it contains a pair of solar arrays and a rotary joint so the panels can track the sun.

NASA is considering relaxing post-Columbia flight rules stipulating daytime launches and good lighting when the shuttle's fuel tank is jettisoned 8 1/2 minutes after liftoff when the shuttle is thousands of miles away.

RULES SHORTEN LAUNCH WINDOW NASA imposed the new rules to make sure cameras would have a clear view of the shuttle's fuel tank and any debris that comes off during ascent.

A chunk of foam insulation that popped off Columbia's tank during launch caused the ship's destruction 16 days later as it returned through the atmosphere for landing.

The foam had hit the ship's wing, damaging its heat shield.

Seven astronauts died as the shuttle broke apart over Texas on February 1, 2003.

NASA redesigned the tank to prevent foam loss, but wants to fly at least one more mission in daylight to make sure the modifications fixed the problem. If NASA misses this launch window and sticks to its plan, the next opportunity for Atlantis to fly would be October 26.

NASA has just four years to finish building the 100 billion dollars orbital complex before the shuttles are retired. The station's structural trusses, modules and other major components were designed to be launched only on the shuttles.

Managers had planned to launch Atlantis and its six-member crew last week, but a lightning strike and a storm triggered a series of postponements. The mission already has been delayed more than three years while NASA recovered from the Columbia disaster.

REUTERS SBA KP2140