While the upcoming launch of the space shuttle Discovery will mark the return to flight of NASA's space shuttle fleet, that is only the beginning, and great care is being taken to assure a successful mission throughout, particularly the landing, wherever it might take place.

To ensure a safe return of Discovery's astronaut crew, shuttle officials at NASA's Dryden Flight Research Center and Edwards Air Force Base have conducted training drills in the off-chance the orbiter makes a West Coast landing instead of touching down at Kennedy Space Center (KSC) in Florida as planned.

"We try to have one major practice about every six months," said Joe D'Agostino, head of Dryden's shuttle support office, during a telephone interview. "That includes getting the whole NASA, Air Force, Army and Navy team together to practice a contingency operation."

While KSC is NASA's preferred landing site for Discovery's STS-114 flight, as well as all shuttle missions since 1990, the space agency turns to Edwards Air Force Base, Calif. and White Sands, N.M. when weather conditions make a Cape Canaveral landing impossible. Thunderstorms, wind speeds and cloud ceilings will all play a role in whether shuttle flight controllers opt for a contingency landing, shuttle officials said.

"Basically, what we're looking for is no thunderstorms and, obviously, no rain," said STS-114 ascent/descent flight director LeRoy Cain. "We're not going to risk flying through rain if it is within 30 miles (48 kilometers) of KSC."

Discovery's STS-114 mission is NASA's first bid at resuming space shuttle flights after the 2003 Columbia accident that led to the loss of one orbiter and the deaths of all seven STS-107 astronauts. The Columbia orbiter broke apart during re-entry Feb. 1, 2003, about two weeks after sustaining wing damage during launch.

Shuttle engineers have spent the last two years revamping Discovery and its sister ship Atlantis to increase flight safety. They have also redesigned portions of orbiter external tanks to reduce the shedding of potentially damaging foam debris. The Columbia Accident Investigation Board concluded that the wing was breached shortly after launch when it was struck by foam debris that fell off part of the external tank system. Discovery is now set to launch toward the International Space Station (ISS) no earlier than July 13, 2005, and return to Earth about 12 days after liftoff.

Gearing for launch, preparing for landing

While NASA has focused much of its attention on minimizing, if not eliminating the same type of launch debris that doomed Columbia, there are new concerns for landings as well, NASA officials said.

"If there's the possibility of debris coming off an orbiter, we'll want less exposure to the public and that might favor a [landing] scenario at White Sands rather than Dryden or KSC," D'Agostino said. "Our first and foremost requirement [in addition to astronauts] is the safety of the general public."

Search teams collected 83,000 pounds (37,648 kilograms) of the debris that rained down from the Columbia orbiter, primarily over Texas, as it crumbled during reentry.

"We were very fortunate during the tragedy of STS-107 that we did not injure anyone on the ground," D'Agostino said.

If Discovery's STS-114 mission goes according to plan, the shuttle should land at KSC during daylight, though NASA officials said it is not a flight constraint.

"We have a daytime launch constraint, which puts us in a daytime landing," Cain told SPACE.com.

Shuttle officials set the daylight launch constraint for Discovery's STS-114 flight, and NASA's follow-up STS-121 mission aboard Atlantis, in order to allow good observation conditions for ground and air-based cameras.

Cain, who also oversaw Columbia's reentry, said Discovery's landing conditions must include at least five miles (8 kilometers) of range visibility, with cross winds not exceeding 15 knots among other constraints. The surface wind criteria, he added, protect the orbiter from putting too much pressure on its landing gear struts.

A California landing

The last shuttle to land at Edwards was Endeavour during the STS-111 mission in June 2002, but Dryden and military officials are always prepared to receive an orbiter.

"It's really weather-driven," D'Agostino said, adding that his crews are on alert when shuttle landings near. "We went four and a half years without a landing, and then had four in a row, so you never can tell."

Originally tapped as the prime shuttle landing site, Edwards Air Force Base is fully equipped with the necessary hardware and support crews to not only safeguard an orbiter after the wheels stop, but also turn it around shipment back to KSC atop a modified 747 aircraft.

"That will be the first site I look at, and primarily it's because there we have a little bit better understanding of the weather," Cain said. "But more importantly, there is more support in the post-landing...[Edwards] is a fully augmented landing site."

While White Sands is still a safe alternative, Edwards has history in its corner, NASA officials said. There have been 49 shuttle landings there since 1981, as well as test approaches and landings with the Enterprise vehicle in 1977.

"We very concerned with [this] mission, and with it going to the ISS, we certainly want to ensure that those crews get the best attention that they can," said D'Agostino of the shuttle astronauts.