Goodbyes, and a Blast Home

With hugs, handshakes and the traditional tolling of a farewell bell, the shuttle Discovery’s astronauts said goodbye Saturday to their comrades on the International Space Station and fired thrusters to send their fragile spacecraft back to Earth.

Discovery Commander Eileen Collins thanked the station crew, Russian cosmonaut Sergei Krikalev and American astronaut John Phillips, for “memories that will last forever.”

With that, the seven members of Discovery’s crew closed the hatches and undocked from the space station, where they had spent the previous eight days.

Under the control of Collins, who has said she can hardly wait to get back to Earth and have some Mexican food, Discovery flew around the station before moving off to finalize preparations to reenter Earth’s atmosphere.

The landing is scheduled for Monday at 1:43 a.m. PDT. If the weather in Florida does not allow a landing at Kennedy Space Center, Discovery could land Tuesday at Edwards Air Force Base in the California desert.

Today, the crew plans to check the flight-control system and tie down loose items in anticipation of the bumpy ride into the atmosphere, which will slow the craft from 17,500 mph to a safe landing speed.

Despite a series of glitches that bedeviled the flight -- the first since the Columbia tragedy in 2003 -- the Discovery astronauts appeared almost giddy as they gathered for the farewell ceremony. They glided back and forth in the weightless atmosphere and hung from the ceiling of a laboratory. Collins shed her buttoned-down image to perform mock pull-ups.

“We’re not glad to see you go,” Phillips told them.

Discovery’s visit was a godsend for the space station, which had been limping along since the Columbia accident with infrequent visits from Russian supply ships.

Discovery’s crew delivered 12,000 pounds of food, water and equipment, repaired a faulty gyroscope, replaced a second one and installed a kind of space toolshed to make things more comfortable for the station crew.

“The pantries are full,” said N. Wayne Hale Jr., deputy shuttle program manager. “We accomplished everything we set out to do.”

Discovery will return with 7,000 pounds of trash and broken equipment.

“We were waiting for this flight for more than two years,” Krikalev said.

It remains uncertain when the next shuttle will arrive. NASA grounded the fleet after a large piece of foam insulation fell off the external fuel tank during Discovery’s July 26 launch.

Although the foam didn’t hit Discovery, the incident embarrassed NASA, which spent hundreds of millions of dollars redesigning the fuel tank to prevent big foam pieces from coming off.

The chunk of foam shed on liftoff was almost the same size as the one that tore a hole in Columbia’s left wing in 2003. During reentry, super-heated gases poured into the hole and broke up the craft, killing its crew.

NASA appointed a special engineering team to study what happened this time. Its first report is due next week.

One clue is that the site of the foam loss is where the insulation is applied by hand instead of machine. If the foam shedding is shown to be human error, and if the flaw can be corrected quickly, the shuttle could return to flight in September.

If not, the delay could make it harder for NASA to finish construction of the half-built space station in time to retire the shuttle fleet in 2010.

The foam was only the first problem for this flight. Two protruding spacers, known as gap fillers, placed between Discovery’s heat-resistant tiles required a first-ever spacewalk to the underside of the craft to remove them.

Just as that problem was solved, engineers became worried about whether a torn insulating blanket under a cockpit window might fray during reentry. Under one scenario, a small piece of the blanket could come off and hit the tail, ripping a hole in it.

Engineers ultimately decided the danger was remote. Further, they couldn’t figure out how to fix the problem without making it worse. So they left it alone.

Though the torn blanket remains a threat during landing, it was evident Saturday from the smiles around the Johnson Space Center in Houston that NASA managers were delighted with the results of this flight.

Yet the celebrations must wait until the wheels stop Monday morning.

“I don’t know if I’d use the word euphoria,” said Paul Hill, the lead flight director. “We are going to be pretty darned happy.”

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Return to Earth

The process of bringing the space shuttle back to Earth takes about an hour. During its reentry and landing phases it is unpowered, so its approach must be perfect -- there is no opportunity for a do-over.

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Reentry

1 - An hour before landing, steering jets spin the shuttle so it’s flying tail-first, and slow it down slightly from 17,500 mph.

2 - Before entering Earth’s upper atmosphere, the shuttle re-orients to nose-first position at a 40-degree angle.

3 - Plummeting to an altitude of 160,000 feet, some shuttle surfaces may reach 3,000 degrees Fahrenheit.

4 - During descent, the shuttle performs four banking maneuvers in the shape of an elongated S, rolling as much as 80 degrees in order to slow.

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Approach and landing

1 - Shuttle angle drops from 40 degrees to 14. Speed drops to subsonic at 50,000 feet as the commander takes over flight control from computers.

2 - At 10,000 feet, 90 seconds before touchdown, the shuttle pitches into a 20-degree glide slope.

(Airliners typically descend at three degrees.)

3 - The shuttle is steered to one of two imaginary cylinders on either side of the runway.

4 - Touchdown occurs 2,500 feet past the start of the runway at about 200 mph; brake parachute helps slow the shuttle to a stop.

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Source: NASA; Graphics reporting by Tom Reinken