CAPE CANAVERAL, Fla. (AP) - The historic next-to-last space shuttle launch was scratched Friday because of mechanical problems, spoiling a visit from the president and dashing the hopes of the biggest crowd of spectators in years, including the mission commander's wounded wife, Rep. Gabrielle Giffords.
NASA hopes to try again Monday to launch space shuttle Endeavour on its final voyage.
President Barack Obama and his family visited Kennedy Space Center anyway but it was unclear whether he would still meet with the Arizona congresswoman. Giffords, who is recovering from a gunshot wound to the head, has been in Cape Canaveral since Wednesday to attend her husband's launch.
Giffords left her Houston rehabilitation hospital for the first time to travel to Florida. It was not immediately known whether she would stay for another try or return to Houston.
She had been expected to watch the liftoff in private - as were the other astronaut families.
Endeavour was fueled and the six astronauts were heading to the launch pad when the countdown was halted, about 31â„2 hours before the 3:47 p.m. liftoff. NASA's silver-colored astrovan did a U-turn at the launch control center and returned them to crew quarters.
It would have been the first time in NASA history that a sitting president and his family witnessed a launch; Obama is not planning to return. As a consolation, Obama and his family got an up-close look at Atlantis. It will make the last shuttle flight this summer as NASA winds up the 30-year-old program and retires the fleet to museums.
Launch director Mike Leinbach said the next launch try would be Monday at the earliest - and hinted at an even longer delay. Technicians will have to crawl into the engine compartment to track a suspected electrical short in a power distribution box.
"We'll fly no orbiter before its time, and today she just wasn't ready to go," Leinbach said.
As many as 700,000 spectators had been expected to crowd nearby coastal communities. For days, police have been warning of massive traffic delays.
At the press site at Kennedy Space Center, astronaut James Kelly, a two-time shuttle pilot, took the news in stride. "When you have technical problems, you delay. That's it. You delay," he said.
Since arriving in Florida aboard a NASA jet on Wednesday, Giffords' whereabouts have been kept secret. Her doctors had said she was "medically able" to travel and that they viewed the trip as part of her rehabilitation.
After the launch was called off, a close family friend who was in Florida to see the launch said her family and staff were deciding whether Giffords should stay or return to Houston. The friend, who asked not to be named because he was not authorized to speak for the family, said the decision is not based on her health, but rather logistics.
In late morning, one of the two prime heaters for a fuel line feeding one of Endeavour's three auxiliary power units failed. At the same time, another heater was acting up.
Leinbach said both main heaters need to be operating for redundancy. The power units provide hydraulic pressure to the main engines at liftoff and to the rudder and speed brake during landing.
The short appears to be in a switchbox or an electrical line leading to it, Leinbach said.