The space shuttle Discovery fired its engines for a critical deorbit burn Tuesday, beginning the most critical phase of the shuttle fleet's return to flight after a 2 1/2-year gap.
Mission Control reported no problems as the shuttle plunged through the atmosphere over the Pacific and began enduring the period of maximum heating, about 20 minutes before touchdown. Touchdown at Edwards Air Force Base in California was set for 8:12 a.m. ET.
Two earlier landing opportunities at Kennedy Space Center in Florida were called off because of rain and thunderstorms in the area.
“How do you feel about a beautiful clear night with a breeze down the runway in the high desert of California?” Mission Control radioed the shuttle.
“We are ready for whatever we need to do,” replied commander Eileen Collins.
The shuttle’s flight path will have it crossing over the Californian coast between Oxnard and Ventura, north of Los Angeles, before landing at Edwards in the Mojave Desert. It will be the 50th shuttle landing at Edwards since 1981.
NASA would have preferred to land the space shuttle at Kennedy to avoid the several days and estimated $1 million needed to ferry the spacecraft back from the West Coast atop a modified jumbo jet. However, rain and thunderstorms off the Florida coast curtailed that option. Discovery also bypassed two Florida landing attempts on Monday owing to low clouds.
The detour to the opposite coast was a big disappointment for the astronauts’ families, who had been waiting to greet their loved ones in Cape Canaveral. Their reunion was put on hold until Wednesday, when they all planned to meet in Houston.
NASA’s top officials also had gathered at Cape Canaveral to welcome the crew home.
“There’s nothing more that I would love to see than it here so everybody here could be a part of this. But it’s not going to be,” said shuttle program manager Bill Parsons. “I want it to be safe, wherever the safest place is to go.”
Added Bill Readdy, an ex-astronaut who heads NASA’s spaceflight office: “All you have to do is look around and see the flashes of thunder and lightning. Obviously, Mother Nature doesn’t want us to land at the cape today.
Collins was understanding. She said her crew was familiar with Florida storms and was “not surprised at all.”
The crew changed into pressurized orange flight suits, helmets, gloves and boots worn during launch and landing. Each astronaut also strapped on a parachute pack, including a life raft, sea dye and two liters of emergency drinking water. NASA instructed the astronauts to begin drinking large amounts of fluids, which are necessary to ease the transition from the weightless environment of space back to Earth’s gravity.
During the descent, Discovery must decelerate from an orbital speed of more than 17,000 mph — an experience that the shuttle's pilot, Jim Kelly, has compared to riding on a runaway freight train. As the shuttle blasts through the atmosphere, it becomes engulfed in a cloud of plasma that approaches temperatures of 3,000 degrees Fahrenheit (1,650 degrees Celsius).
"It is almost like a tornado of fire behind you," veteran astronaut Dave Wolf recalled.
Critical phase
The landing delays marked just the latest schedule shifts for Discovery, which launched on its mission to the international space station on July 26. The launch itself was delayed for 13 days due to a fuel gauge glitch, and the mission was later extended to give more time for transferring supplies to the space station. The mission, originally intended to last 12 days, has now spanned 14.
Landing is the most critical phase of the shuttle fleet's return to flight after a 2 1/2-year gap in the wake of the Columbia accident. It was during re-entry that the shuttle Columbia disintegrated in February 2003 over Texas, killing all seven astronauts aboard and grounding the shuttle fleet. Investigators concluded that flying foam insulation from the shuttle's external fuel tank cracked a hole in the left wing, allowing superheated atmospheric gases to enter and destroy Columbia from within.
NASA responded to the disaster by making dozens of upgrades in the shuttle and its tank, and also subjecting Discovery to the most exhaustive on-orbit inspection ever. NASA set up scores of cameras to record Discovery's launch and built a new kind of laser- and camera-equipped inspection boom to survey the shuttle's protective skin while on orbit. During one of the mission's three spacewalks, Discovery astronauts Stephen Robinson and Soichi Noguchi tested patches and fillers that could be used to mend gaps in the shuttle's tiles or reinforced panels.
Discovery's crew delivered tons of supplies to the station, and for the return trip, they loaded the shuttle with tons of trash and old equipment from the station. Robinson and Noguchi also repaired one of the station's gyroscopes and replaced another one, bringing the station's four-gyro guidance system to full strength for the first time in three years. During the third spacewalk, they installed a storage platform on the station for future construction jobs — and then Robinson took an unprecedented ride on the station's robotic arm to Discovery's tile-covered belly, where he removed two protruding gap fillers by hand.
After Discovery's launch on July 26, NASA officials said they were surprised to see that the shuttle's external fuel tank shed more debris than expected, including a pillow-sized, 1-pound (450-gram) piece from an area known as the protuberance air load ramp, which had not been redesigned after the Columbia tragedy. Mission managers said the problem with the foam debris and the gap fillers would have to be resolved before another shuttle lifts off. In all, deputy shuttle program manager Wayne Hale said 47 items “great or small” would be considered and rectified before the next launch.
Currently, the shuttle Atlantis is due to fly another test mission to the space station no earlier than Sept. 22, but Hale said he didn't consider that "a serious launch date." If Atlantis doesn't lift off by Sept. 24, the next opportunity would be in early November.