Technicians at the Kennedy Space Centre in Florida started filling space shuttle Atlantis‘ fuel tank for a launch attempt on Friday after nearly two weeks of delays due to weather problems and technical glitches, officials said.
Lift-off is targeted for 11.41am (3.41pm GMT) and meteorologists predicted a 70% chance the weather would be suitable for launch.
The shuttle and six astronauts are on a mission to resume construction of the International Space Station, halted after the destruction of shuttle Columbia more than three-and-a-half years ago.
The United States space agency is already working on borrowed time, having wrangled extensions for launch attempts after negotiations with its prime space station partner, Russia.
Originally, Nasa’s window of opportunity to launch Atlantis to the space station closed on September 7.
Now the agency has until Saturday, if necessary.
Nasa tried to launch Atlantis as early as August 27, but a lightning strike at the launch pad and then the threat of a tropical storm triggered a week of delays.
The flight was rescheduled for Wednesday, but that attempt ended shortly before fuelling when a motor inside a critical power unit aboard the shuttle failed to operate as expected.
After two days’ debate about the condition of the device, Nasa late on Thursday decided to proceed with a final attempt to launch the shuttle this week.
More than 1,8-million litres of cryogenic propellants began flowing into the shuttle’s 47m tall fuel tank around 3am EDT (7am GMT) after managers cleared Atlantis for a planned 11-day flight.
The primary goal of the mission is to deliver and install the station’s second set of power-producing solar arrays.
The mission has already been delayed more than three years while Nasa recovered from the 2003 Columbia disaster.
Since the accident, which claimed the lives of seven astronauts, Nasa has flown two test missions to check safety improvements made after the disaster.
The accident was traced to a piece of foam insulation that fell off Columbia‘s fuel tank during launch and smashed into the ship’s wing, damaging its heat shield. The shuttle broke apart as it flew through the atmosphere toward landing.
Despite two redesigns of the fuel tank, managers still expect foam to fly off during launch, but the debris is not expected to pose a threat to the shuttle.
A third tank redesign is under way.
The modifications were not ready in time to be tested on shuttle Discovery‘s flight in July but Nasa approved that mission, as well as that of Atlantis, because even under the worst-case scenario the crew would not be at risk, shuttle program managers said.
If the shuttle were too badly damaged to safely return home, the astronauts would stay aboard the space station until a rescue mission could be launched. That option was not available to the Columbia crew.
Nasa now requires its crews to conduct extensive in-flight inspections to assure the heat shield is safe for reentry.
The agency plans one more space station assembly mission this year. The outpost needs to be finished by 2010, when the shuttle fleet is scheduled for retirement. – Reuters