NASA postponed the launch of space shuttle Atlantis to resolve a fuel-sensor problem and said it would be Saturday at the earliest before they tried again.
Atlantis was due to start its 11-day mission on Thursday, but the launch was called off after two sensors in its external tank failed a routine check.
Engineers believe the sensor problem, which cropped up while the shuttle was being filled with fuel for the space freighter’s 8.5-minute sprint to orbit, was due to an open circuit.
Managers met all afternoon and into the evening, planning out the next steps for the launch team. Initially, sources said it looked as if a Friday launch might be possible, but ultimately the managers decided to take more time for troubleshooting the spurious sensor readings.
"It was our determination that we need more time, and so we downloaded from the 24-hour scrub turnaround to a 48-hour scrub turnaround," said LeRoy Cain, chairman of the pre-flight mission management team.
NASA has until Dec. 13 to launch the mission this year and take Europe’s Columbus science laboratory to the space station. Atlantis must leave the station before the angle of the sun’s rays change, which would overheat the orbiter.
The shuttle uses more than 500,000 gallons (2.2 million liters) of cryogenic hydrogen and oxygen to get into orbit. Four engine cut-off sensors in the shuttle’s fuel tank monitor levels of liquid hydrogen during the ascent. The launch could have gone forward if only one of the sensors failed — but two of them gave bad readings on Thursday.
The sensors are part of a backup safety system to shut down the shuttle’s main engines once the shuttle reaches space or if a problem occurs after liftoff. If the engines continued to run once the fuel supply was gone, an explosion could destroy the orbiter.
Engineers need to drain the tank and verify that all the sensors are working as they go dry, NASA said in a statement. If the problem persists, managers might institute a workaround plan using other readings from the shuttle to monitor fuel levels, Cain said.
NASA wrestled with a series of fuel-tank sensor problems as it attempted to resume shuttle flights following the 2003 Columbia accident. The first post-Columbia mission in July 2005 was delayed 13 days due to sensor glitches.
Engineers traced the problem to a bad batch of sensors and replaced them.
Launch director Doug Lyons told reporters he was confident that the shuttle would be ready for liftoff at 3:43 p.m. ET Saturday, assuming that the troubleshooting proceeded as his team expected. The chances of acceptable weather for launch were set at 60 percent.
Disappointment for Europeans
Tucked inside Atlantis’ cargo bay as it waited for another launch opportunity was the European Space Agency’s primary contribution to the space station program — a 22-foot-long (7-meter-long), 14-foot-diameter (4.5-meter-diameter) laboratory named Columbus.
Germany’s Hans Schlegel and Leopold Eyharts of France will join five U.S. astronauts on the mission — commander Stephen Frick, pilot Alan Poindexter, flight engineer Rex Walheim, Leland Melvin and Stanley Love.
Thursday’s postponement was a disappointment for the ESA. The $2 billion lab has been in the works for nearly a quarter-century, and was held up for years by NASA’s repeated space station design problems and, more recently, the 2003 Columbia tragedy.
“Of course, we would love to fly on time, but we want to fly when it’s safe,” said Alan Thirkettle, the European space station program manager.
The three astronauts aboard the international space station also were disappointed by the news.
Frick passed on some consoling remarks through Mission Control.
“He says that he’s sorry they’re going to be a little bit late and they’ll get there as soon as they can,” Mission Control radioed the space station crew. “Aw, that was sweet,” commander Peggy Whitson replied from orbit.
The launch was still more than eight hours away when the sensor problem cropped up, and the crew had not yet climbed aboard.
The postponement ended NASA’s streak of on-time shuttle launches for the year. Each of the year’s previous three countdowns ended in on-the-dot departures.
This report includes information from msnbc.com, Reuters and The Associated Press.