The Endeavour flight marks the 25th and final voyage for the shuttle, the youngest shuttle in what once was a four-orbiter fleet. When wheels touch the runway again on June 1, the orbiter will have logged more than 115 million miles in space.
Atlantis, the final orbiter remaining, is expected to make its final NASA shuttle launch in July.
For spectators, including US Rep. Gabrielle Giffords (D) of Arizona, whose husband is commanding the mission and who is recovering from a gunshot wound received in during a January shooting rampage in Tucson, Ariz., Endeavour's liftoff was as close to a "blink and you'll miss it" launch as they come.
Roughly 12 seconds after the engines ignited, the orbiter vanished into a low-hanging layer of clouds, visible beyond that point only to tracking cameras on the ground at a cloud-free site north of the launch pad, and to an aircraft operated by range-safety officers with the US Air Force.
"It was a fantastic launch," said Michael Moses, who headed the prelaunch mission management team. But "we apologize that the view wasn't the best."
The launch team has rules it must follow regarding permissible launch weather, but those rule don't cover "how long you can watch before the launch goes out of sight," he quipped during a post-launch new conference.
Heater problem fixed
Endeavour originally was slated to begin its trip to the International Space Station on April 29. But the launch team scrubbed the liftoff during the final countdown because a key component related to one of the orbiter's auxiliary power units was misbehaving.
The auxiliary power units run the hydraulic systems that operate landing gear, flight-control-surfaces on the wings and tail, and the gimbals that swivel the shuttle's main engines to provided steering during ascent. The troublesome component was a heater designed to keep the fuel lines to one of the units from freezing while the shuttle is on orbit.
Technicians traced the problem to an electrical switch box in the orbiter's aft section. They made the necessary repairs, and the heater performed as advertised.
"We can declare that a victory," says Peter Nickolenko, the assistant launch director for the mission.
In addition, crew members will conduct four spacewalks, the final four of the shuttle program. Space-suited mission specialists will swap out experiments on the station's exterior, perform a range of maintenance chores, and fine-tune the installment of Endeavour's robotic arm as part of the station's robotic-arm system.
The extra length of boom will help spacewalking station crew members travel to locations on the station they wouldn't be able to reach otherwise.
End of an era for ESA
This mission also marks the final trip for a European Space Agency astronaut aboard the shuttle – mission specialist Roberto Vittori. It has been a route to space for Europeans that predates the space-station program.
The first ESA astronaut to make the trip to orbit on a shuttle was Ulf Merbold, who flew aboard Columbia during the first Spacelab mission in late 1983. The lab, a pressurized research facility that fit into the shuttle's cargo bay, in effect was the forerunner to ESA's Columbus lab module, which NASA would install at the space station 25 years later.
Michel Tognini, a former ESA astronaut who now heads the agency's astronaut center in Cologne, Germany, notes that ESA now has undertaken 86 shuttle missions with NASA, either with ESA astronauts aboard or with ESA-built hardware nestled in an orbiter's cargo bay.
International cooperation, exemplified in ESA's long relationship with NASA, "is essential for the future of human space exploration," he said.