CAPE CANAVERAL, Fla. -- With thunderheads pressing in on the launch site in central Florida, NASA managers canceled yesterday's liftoff of the space shuttle Discovery. The launch has been rescheduled for today at 3:26 p.m.
"This is a dynamic day. I think we're playing it too close here," said Steve Stich, the flight director at Johnson Space Center in Houston.
Launch Director Mike Leinbach at the Kennedy Space Center told shuttle commander Steve Lindsey, "Well, Steve, sorry to break your string." Lindsey's previous three shuttle launches had all gone off without a hitch.
Officials made the call minutes before the scheduled launch at 3:49 p.m.
Weather forecasts are for rain and thunderstorms moving east across the coast of central Florida for the next few days, a typical summer weather pattern for the Southeast.
NASA regulations prohibit a launch in heavy clouds or when thunderstorms are within 20 nautical miles of the launch site. The fear is that the vehicle could trigger outbreaks of lightning as it streaks through the clouds, which could in turn knock out the shuttle's electronics.
To find a proper vector for its rendezvous with the orbiting International Space Station, the shuttle can launch only within a 10-minute period each day.
This is the shuttle's 115th mission and the second test flight since the loss of Columbia in 2003.
During the 12-day mission, the seven-member crew is scheduled to deliver 2 tons of cargo, including a second oxygen generator, to the space station. One of the crew, European Space Agency astronaut Thomas Reiter, will stay aboard the space station when Discovery departs, the first time since the Columbia disaster that the station will have a three-person crew.
NASA worked on another late problem yesterday, the failure of a thermostat controlling a heater on one of the small thrusters near the tail of the craft. Since there are 44 thrusters, launch officials decided the crew could work around the problem.
The weather, however, would not yield. The specific problem was "anvils," which are the tops of thunderheads that can carry a charge. The anvils were parked off to the west much of the morning and afternoon, but one moved within the 20-mile limit minutes before the launch time.
"We can't control the weather," Leinbach said after the launch was scrubbed. "We're not going to launch a vehicle unless it's safe to do so."
The problem with scrubbing launches is not just the inconvenience. Each launch day, the fuel tank must be filled with 535,000 gallons of liquid oxygen and hydrogen.
When the launch is scrubbed, the tank is emptied. This repeated fueling process is thought to put a stress on the insulating foam that covers the tank, allowing tiny cracks to develop. But each tank is allowed 13 fueling cycles, so it should not be a problem, NASA said.
If the scheduled launch today is scrubbed, NASA managers are considering taking the day off tomorrow before starting the process again.
John Johnson Jr. writes for the Los Angeles Times.