Flying upside down and backwards just off the tip of Madagascar over the Indian Ocean, shuttle commander Eileen Collins and pilot James Kelly fired Discovery's twin braking rockets at 7:06:18 a.m. EDT to begin the hour-long descent to a California landing.
The deorbit rocket firing lasted two minutes and 42 seconds, changing the shuttle's velocity by about 187 mph and dropping the far side of its orbit deep into the atmosphere. Touchdown on runway 22 at Edwards Air Force Base, Calif., is expected at 8:12 a.m. EDT, 54 minutes before sunrise local time.
CBS News Space Consultant William Harwood reports this would be the 50th shuttle landing at Edwards Air Force Base and the first since June 2002. The touchdown, before dawn California time, would make Discovery's return the first night shuttle landing at Edwards since September 1991 and just the sixth overall in program history.
Discovery had no luck earlier Tuesday as it orbited the earth hoping for clouds, rain and lightning storms to move away from the Kennedy Space Center at Cape Canaveral, NASA's preferred location for shuttle landings.
NASA first tried to bring Discovery back to Florida Monday - but failed, twice, due to bad weather - and things went pretty much the same this morning, as the astronauts aimed at, and then were waved off of, landing slots for 5:07 a.m. and 6:43 a.m. EDT at Cape Canaveral.
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Discovery on its way back to Earth.
"How do you feel about a beautiful clear night with a breeze down the runway in the high desert of California?" Ham radioed Discovery as the shuttle crew waited for permission to try or skip a Florida landing.
"We are ready for whatever we need to do," replied Collins.
"What we had is continued instability at the Cape. Just within the last 15 minutes or so, we had another couple of small cells popping up around 15 to 20 miles that came out of nowhere, just off the coastline and growing. Predicted to have some lightning activity here shortly," said astronaut Ken Ham in Houston. "So the official forecast is holding electrified clouds off the coast of the Cape, which we're not going to send you through."
If the weather at Edwards deteriorates, NASA still has one more place to bring the shuttle down: the White Sands Missile Range in New Mexico. That's considered to be unlikely, however; rain is also a possibility at White Sands.
The directions to redirect toward California came just minutes after controllers told Collins the weather seemed to be clearing in Florida and they hoped to get the crew to the Kennedy Space Center. Conditions then took a turn for the worse.
Collins was understanding. She said her crew was familiar with Florida storms and was "not surprised at all."
"I've been in your shoes many times so I understand," Collins told Mission Control.
NASA instructed the astronauts to continue landing preparations and begin drinking large amounts of fluids, which are necessary for re-entry because bodily fluids are lost in the weightless environment of space.
The astronauts began their day with a chorus of "Good Day, Sunshine," the Beatles standard played by NASA Mission Control as it woke up the shuttle crew for the day they hope will be their return to Earth.
"We sure hope we get our feet on the ground today," astronaut Wendy Lawrence responded.
NASA ordered the astronauts aboard space shuttle Discovery to bypass today's first two landing opportunities because of stormy weather off the Florida coast.
"At this time, we're going to ask you guys to watch the earth go by for one more rev [revolution]," Mission Control told shuttle commander Eileen Collins. "We do appreciate your patience and good humor with the situation."
Earlier Tuesday, the astronauts had powered up their spacecraft and closed Discovery's payload bay doors as they awaited word on which, if any, of several landing opportunities they would attempt.
Monday's delay disappointed astronauts' families, who anxiously awaited Discovery's return. The mission, originally intended to last 12 days, has now spanned 14.
Discovery has enough fuel and supplies to stay in orbit until Wednesday, but NASA wants to hold out that option only if a technical problem arises.
Discovery is the first shuttle to return to orbit since Columbia's catastrophic re-entry in 2003. But Discovery's launch and flight to the international space station could be the last for a long while.
NASA grounded the shuttle fleet after a nearly 1-pound chunk of insulating foam broke off Discovery's external fuel tank during its July 26 liftoff - the very thing that doomed Columbia and was supposed to have been corrected.
Another day was added to the mission when NASA grounded its fleet so astronauts could do additional work on the station. Discovery was the first shuttle to visit the orbiting outpost since 2002.
As a result of Columbia, Discovery's crew performed intense inspections of their ship on five different days. Astronauts also did a spacewalk to test new repair techniques and replaced a failed gyroscope on the station during another spacewalk.
In a third, unprecedented spacewalk, two protruding thermal tile fillers were removed from Discovery's belly. Engineers feared the material could cause dangerous overheating during re-entry.
Columbia was doomed by a 1.67-pound piece of foam that broke free from an external fuel tank at launch. The foam pierced a hole in the ship's left wing, and as the spacecraft re-entered the Earth's atmosphere, searing gases melted the wing from the inside. All seven astronauts aboard were killed.
Former shuttle astronaut Charles Bolden said there comes a time when every astronaut is ready to return home - no matter how risky the ride.
"You always want to stay in space. You don't ever want to come home, but you invariably get homesick," he said. "With every orbit that you don't come home, it gets more and more frustrating."