CAPE CANAVERAL, Fla. – A historic space shuttle launch was scratched Friday for mechanical problems, spoiling a visit from the president and dashing hopes of guests like astronaut-wife, congresswoman Gabrielle Giffords and the biggest crowd of spectators in years.
NASA hopes to try again Monday to launch space shuttle Endeavour on its final voyage, the next-to-last shuttle flight.
President Barack Obama and his family still planned to visit Kennedy Space Center for a tour but it was unclear whether he would meet with the wounded Giffords, wife of the shuttle's commander. She is recovering from a gunshot wound to the head, and it was not immediately known whether she would stay in Florida for another try or return to Houston.
Giffords hasn't been seen publicly since the Jan. 8 assassination attempt. She left her rehabilitation hospital in Houston on Wednesday for the first time to travel to Florida for her husband's launch.
The Arizona congresswoman, who has difficulty walking and talking, was expected to watch the 3:47 p.m. liftoff in private with other astronauts' families.
"Bummed about the scrub!! But important to make sure everything on shuttle is working properly," her staff said via Twitter.
Launch director Mike Leinbach said the next try would be Monday at the earliest — and hinted at even a longer delay. Technicians will have to crawl into the engine compartment to track a suspected electrical short in a power distribution box, and that will take time.
Leinbach said the delay was "unfortunate" for commander Mark Kelly and his crew. The six astronauts were en route to the launch pad when the countdown was halted. NASA's silver-colored astrovan did a U-turn at the launch control center and returned them to crew quarters.
"It's the nature of our business," Leinbach said. "We'll fly no orbiter before its time, and today she just wasn't ready to go."
The news took guests by surprise as well as journalists who were outside watching the astrovan drive by. There was confusion when the van pulled into the driveway in front of launch control and parked there for several minutes, rather than head straight for the pad three miles away. Then the official announcement came over NASA's broadcast lines.
Tammi Flythe, among the thousands gathered across the Indian River in Titusville with her two children, was crushed. They traveled in from Tampa.
"I really wanted my son to experience this," she said.
Alex Thomas of Jacksonville also was devastated.
"We had planned this for several days," he said. "My wife has to work this weekend so we may have missed the chance to see our first launch."
As many as 700,000 people were expected to crowd nearby coastal communities. For days, police have been warning of massive traffic delays. After Endeavour, there's only one more space shuttle flight — by Atlantis — before NASA ends the 30-year-old program and retires the fleet to museums.
Astronaut James Kelly, a two-time shuttle pilot, took the news in stride at the press site at Kennedy Space Center. "When you have technical problems, you delay. That's it. You delay," he said.
"Of course, it's always disappointing, especially for the crew," added astronaut Clayton Anderson, a former space station resident. "NASA has a great safety record and they're going to do it the right way. They're going to pull it back and do what's right. They have to."
Since arriving aboard a NASA jet on Wednesday, Giffords whereabouts have been keep 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 said her family and staff were deciding whether Giffords should stay in Florida or return to Houston as soon as possible. The friend, who asked not to be named because he was not authorized to speak for the family, says the decision is not based on her health, but rather logistics.
In late morning, one of the prime heaters for the fuel line powering one of Endeavour's three auxiliary power units failed. At the same time, another heater was acting up.
Leinbach said both 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.
Endeavour's upcoming mission to the International Space Station is the last in its 19-year history. The shuttle was built to replace Challenger, destroyed during liftoff in 1986, and made its maiden voyage six years later.
AP writers Seth Borenstein and Kyle Hightower in Florida and Ramit Plushnick-Masti in Houston contributed to this report.