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Endeavour launch delayed at least 72 hours; Obama visits Giffords

Update at 5:05 p.m. ET: President Obama met with wounded Arizona Rep. Gabrielle Giffords, AP says.

Update at 4:15 p.m. ET: Over at The Oval, our colleague Mimi Hall has the pool report on President Obama's tour of the Kennedy Space Center.

Update at 3:09 p.m. ET: Launch director Mike Leinbach said the earliest that Endeavour would launch would be Monday would be 2:33 p.m. ET.

Engineers believe the problem might be with an aft switchbox known as a Load Control Assembly, or an electrical short in the wires leading into or from the switchbox.

NASA explains what will happen:

Endeavour's external tank will be drained, technicians will enter Endeavour's aft compartment overnight and by tomorrow afternoon, will put in a platform to gain access to the avionics bay where the Load Control Assembly is located. Once there, they will assess whether they need to remove and replace the switchbox, or fix an electrical wiring short.

NASA is holding a news conference now. [Note: Delayed.] Updates to follow.

By Douglas Stanglin
USA TODAY

Update at 2:15 p.m. ET: With a helicopter overhead and a SWAT vehicle in chase, the space shuttle crew had left NASA's operations center in an airstream trailer for the 10-minute trip to the launch pad when word came: Launch of shuttle Endeavour is scrubbed, USA TODAY's Donna Leinwand Leger reports from the Kennedy Space Center.

Her file:

The airstream trailer, seconds from its destination, and the astronauts, less than three hours before a planned launch for a 14-day mission to the International Space Station, abruptly turned around for at least 72 hours of hurry-up-and-wait.
A misfiring thermostat, one of two used to keep a fuel line from freezing, is the culprit, says launch director Mike Leinbach.
"It was a hard failure. We couldn't get it to come to life no matter what we did," Leinbach said.
Another heater farther up the line "was also exhibiting funny behavior," he said. Engineers suspect a short in an electrical box.
"We didn't want to commit to flight with only one heater," which would leave the shuttle at risk for a frozen fuel line if the other thermostat failed, Leinbach said.

Update at 2:13 p.m. ET: President Obama has landed in Florida at the Kennedy Space Center even though the launch of the shuttle Endeavour has been postponed.

Update at 1:41 p.m. ET: USA TODAY's Mimi Hall reports that President Obama will stick to his plan to stop at the space center despite the scrubbed launch. The president will then go on to Miami to deliver a commencement address tonight.

Update at 1:13 p.m. ET: NASA officials now say the launch will be postponed for at least 72 hours, USA TODAY's Donna Leinwand Leger reports from the Kennedy Space Center. The problem has been traced to a thermostat in a heating unit that was not functioning properly, she reports.

Update at 12:57 p.m. ET: Florida Today, our sister publication, reports that the van carrying the astronauts normally stops on the main road leading to the launch pad to drop off the chief astronaut and the pilot who flies the weather reconnaissance aircraft before continuing to the pad.

This time, however, the van pulled into the LCC parking lot and stopped for several minutes before leaving and turning left to head back to the crew quarters at the Operations and Checkout facility.

Update at 12:50 p.m. ET: NASA says there will be "at least a 48-hour scrub turnaround while engineers assess the issue."

Update at 12:33 p.m. ET: The delay was announced as shuttle commander Mark Kelly and his crew were on their way to the launch pad, the Associated Press reports.

NASA reports that two heaters on an auxiliary power unit were not working. The AP says engineers could not figure out the problem and NASA decided to scrub the flight.

President Obama had planned to be on hand for the launch, but had not yet arrived.

Update at 12:29 p.m. ET: NASA has scrubbed today's launch of the shuttle Endeavour because of overheating in two of its five auxiliary heating units, NBC reporter Jay Barbree reports. The delay is expected to take at least 48 hours.

Update at 12:23 p.m. ET: Today's launch of the shuttle Endeavour has been scrubbed for technical reasons. It had been scheduled to launch at 3:47 p.m. ET.

Original posting: The space shuttle Endeavour is fully fueled and undergoing a final inspection for its 3:47 p.m. ET launch today, USA TODAY's Donna Leinwand Leger reports to us from the Kennedy Space Center.

The countdown is now on a planned hold while an inspection team, dressed in orange jumpsuits, carries out its final walk-through and a "Close Out Crew" prepares a White Room, a holding area outside the shuttle hatch, for the crew to enter.

The shuttle mission is commanded by astronaut Mark Kelly, husband of wounded Rep. Gabrielle Giffords, who will be on hand for the launch.

Mission operators are carefully watching the weather. Early today, dark clouds hovered over Kennedy Space Station, limiting visibility.

NASA meteorologists predicted a 70% chance of favorable weather for today's launch. Last night, a night of violent lightning storms delayed for five hours the removal of a protective service station that surrounds the shuttle.

Leger reports that NASA spokesman Allard Beutel says NASA teams loaded 500,000 gallons of liquid hydrogen and liquid oxygen into the shuttle's external fuel tanks today.

A pressure problem in the right fuel tank developed shortly before 9 a.m. ET, but crews were able to alleviate the problem and bring the pressure down, Beutel says.

See photos of: NASA, Endeavour, Mark Kelly