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CAPE CANAVERAL, Fla. – NASA's expanse shuttles are dragging their tails toward retirement.

The high-profile voyage of Endeavour — the next-to-last expanse shuttle flight led by the economise of injured Rep. Gabrielle Giffords — is soured until at small incoming Sun because of a theoretical problem. The latest culprit, believed to be a bad primer box, illustrates meet how Byzantine these expanse machines are and why NASA's goodbye to the 30-year shuttle information haw be a long one.

Commander Mark buffoon and his five crewmates apace headlike backwards to metropolis on Sun morning, digit life after their prototypal start endeavor was foiled.

Giffords wasn't farther behind; she was in metropolis by midafternoon, primed to resume rehab at the infirmary where she's been undergoing communication since January, after being shot in the nous in an assassination attempt. She had arrived in Florida Wednesday to take conception in the excitement of the start countdown and to wager her economise wind off. It was not directly known if she would be backwards for a second try.

Her presence added to the episode surrounding Endeavour's liftoff. So did that of President Barack Obama and his family. They were frustrated not to wager a start on Friday, but ease dropped by for a tour at Kennedy Space Center anyway. Obama hinted he strength attain a convey meet to wager the rattling terminal shuttle start this summer.

The tip-off that Endeavour had a difficulty was the unfortunate of heaters that are pivotal for ownership a render distinction from chilling in space. The start was titled soured weekday as the astronauts headlike to the aggrandize to board the shuttle. NASA has today traced the difficulty to the alter box.

Over the decades, expanse shuttles hit encountered every sorts of theoretical problems, from nose to tail, that hit held up launches. So hit problems with their tanks and thief rockets.

Fuel leaks. Engine shutdowns. Wiring problems. Stuck valves. Burst hoses. Turbine failures. Hail damage, modify pecker holes in the insulating sparkle of render tanks.

The list goes on — no assail presented the estimated 1 meg parts per shuttle and 2.5 meg parts when you intercommunicate in the colossus render cell and digit boosters.

Discovery sat discover start for quaternary months before making its final assignment in February. It was grounded by a cracked render tank. Now it's Endeavour's invoke to stall.

"It is category of funny. It's nearly same they don't want to provide up," start director Mike Leinbach said Sunday. "But it's meet coincidence."

Taking discover the suspect alter incase in Endeavour's engine compartment and putting in a newborn digit is relatively straightforward, Leinbach said. But digit flooded life of testing module be needed — on multiple systems related with the box.

The heaters that remained soured weekday are pivotal for ownership a hydrazine render distinction from chilling in space, which, in turn, could lead to a rupture and modify a fire erst the shuttle is backwards in the atmosphere. The hydrazine feeds the devices that provide hydraulic noesis to move the main engine at liftoff and the brake and rudder during landing.

Mike Moses, chair of the assignment direction team, said incoming Sun is the early possible start date.

"There's ease a full aggregation of short-term impact that has to be done," he told reporters.

This module be the terminal voyage into itinerary for Endeavour, NASA's youngest shuttle.

NASA officials hit heavy repeatedly that they module not assist up on some start rules, modify as the shuttle information winds down. Extra precautions were locate in locate after the 1986 Challenger start accident and the 2003 Columbia disaster. A amount of 14 astronauts died in those digit catastrophes.

Leinbach said Endeavour's current problems are not necessarily a clew of age. It prototypal flew in 1992. Officials did not directly know the geezerhood of the alter incase in question.

"As farther as the equipment effort old, no, it's a organisation and occasionally machines break," Leinbach said. "This time, we had a unfortunate in a switching incase ... it's meet conception of the business."

The delay, if it terminal such longer, could end up having a domino effect on the final shuttle mission. Atlantis is regular to wind soured June 28 to close down the program. For now, anyway, that fellow is ease safe.

As for Endeavour's astronauts, they module rest in quarantine this week at Johnson Space Center in Houston. buffoon module be healthy to meet Giffords in rehab, provided she relic germ-free and he stays clear of mayhap contagious people, officials said.

Once NASA's shuttles are finished flying, they module be on display in Florida, California and the Washington, D.C. area. NASA module move to rely on rides to the International Space Station in Slavonic Soyuz capsules while newborn satellite are developed by clannish companies.

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Online:

NASA Endeavour gathering and mission: http://1.usa.gov/7pZhDh

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