Shuttle launch officials have tweaked liftoff and landing procedures for the first post-Columbia shuttle mission in order to increase safety for both the orbiter’s astronaut crew and observers on the ground.

“The main difference from the flight of Columbia or previous launches has been the redesign of the external tank to prevent debris from bouncing off the orbiter during the launch phase,” said Michael Sarafin, NASA’s guidance, navigation and control (GNC) officer for Discovery’s mission, during a telephone interview.

The tank was redesigned to prevent the same type of critical wound that afflicted the Columbia orbiter when a briefcase-sized chunk of foam insulation broke off the external tank and punched a hole in the shuttle’s left wing leading edge. That damage, investigators found, led to Columbia’s destruction during its re-entry Feb. 1, 2003.

NASA also has made some changes to shuttle launch and landing protocols for Discovery’s flight, including a hard rule that the orbiter liftoff and return to Earth during daylight to give ground-observers a better target for tracking.

“The lighting constraint that we’re going to use for the return-to-flight missions makes it difficult to reach the international space station,” Sarafin said, adding that the regulation puts additional limits on an already restrictive launch window. NASA officials currently plan to launch Discovery and its STS-114 mission crew sometime between May 15 and June 3. Another launch opportunity opens in July. The space agency’s three remaining shuttles have been grounded since the Columbia accident.

To prepare for Discovery’s return-to-flight mission, flight managers have conducted a series of eight-hour simulations during which they practiced multiple launches and landings.

“We are well into our training template for the flight of Discovery,” said Sarafin, who also worked as GNC officer for Columbia’s final mission. “I’m really looking forward to getting back to flying and resuming shuttle operations.”

Meanwhile, NASA has doubled — from 10 to 20 — the number of sites dedicated to capturing high-resolution images and video of Discovery’s launch, with each site containing at least two cameras, according to the space agency’s most recent return-to-flight implementation plan released March 22 .

The report also stated that NASA plans to use two WB-57 aircraft — high-altitude jets with rotating camera systems tucked inside their bulbous, ball turret noses — to capture even more ascent and re-entry views of the first two return-to-flight shuttle launches.

Dubbed the WB-57 Ascent Video Experiment (WAVE), the plan calls for the aircraft to fly at an altitude of about 18,288 meters and catch a 643-kilometer view of Discovery’s launch path. The planes also should track the later stages of re-entry at mission’s end. A 81-centimeter turret at the nose of each aircraft will carry a high-definition television camera and infrared instrument, the implementation plan stated.

On top of that imagery, cameras mounted on both Discovery and its external tank will record launch and tank separation so that information can be relayed to flight controllers to determine the health of the orbiter.

“We want to watch the vehicle and be monitoring for anything out of the ordinary,” Sarafin said, adding that the actual flight operations of the Discovery orbiter and its astronaut crew during launch will be similar to previous missions.

Shortly after launch, NASA officials hope to have a blow-by-blow record of the ascent’s effect on Discovery’s wings. Shuttle engineers have installed a network of 88 sensors behind the leading edges of each wing. Most of them are accelerometers that will be used to detect any impacts that strike the wing. Another 22 sensors on each wing should measure temperature, NASA officials have said.

“The wing leading edge sensor data is really obtained passively,” Sarafin said. “There is a team of engineers who will transfer that data fro m the orbiter and study it on the ground.”

Mission managers also have devised plans to divert Discovery and future shuttles during landing, in the event the spacecraft suffer damage, flight control failure or pose a potential hazard to the regions and people it will fly over on approach.

“There’s never really been a public safety risk policy for any re-entry vehicle outside of a launch range environment,” said NASA safety and mission assurance officer Bryan O’Conner during the teleconference. “We did this so we wouldn’t be in a vacuum.”

During the Columbia accident, NASA flight controllers lost contact with the orbiter while it was flying 61,577 meters above Texas at a speed of about 20,000 kilometers an hour (March 18).

“It turns out that on a space shuttle re-entry, the crew cannot really change the flight plan at high speeds,” explained Bill Parsons, NASA’s space shuttle program manager, during a March 23 teleconference with reporters. “It’s only at lower speeds, airplane speeds, that they can make changes.”

To reduce the risk of a shuttle raining debris on inhabited areas during an emergency, NASA could direct the orbiter to land at fall-back landing strips at New Mexico’s White Sands Missile Range and Edwards Air Force Base in California.

“If there is a problem with the shuttle, we will go with the minimum threat, an alternative landing at White Sands,” O’Conner said, adding that Kennedy Space Center’s Cape Canaveral, Fl a., airstrip will remain the primary target for landing.

O’Conner said that the new policy also covers launches, with NASA establishing spectator-free zones in areas that Discovery will fly over as it returns to Earth. The space agency also will cut back on the number of spectators, with a limit of 20,000 to 25,000 people, that drive out to Kennedy Space Center grounds to watch liftoff.

Meanwhile, flight controllers and managers will continue training up to the last.

“Sitting on the ground for two years is something that no flight controller hopes to do,” said Sarafin, who will hang up his GNC officer hat with Discovery’s flight for a post as flight director. “The most challenging part has been just making sure we’re ready to go.”