Space Shuttle Cleared for Reentry

NASA Keeping an Eye on Weather for Discovery's Landing, Set for This Morning in Florida

Photos
Space Shuttle Discovery Returns to Flight
Space shuttle Discovery, trailing a tail of yellow fire and billowing gray smoke, launched into central Florida's dazzling summer sky Tuesday like an outsize Independence Day Roman candle.

CAPE CANAVERAL, July 16 -- NASA Mission Control cleared the space shuttle Discovery for reentry Sunday in anticipation of a breakfast-time landing Monday at Florida's Kennedy Space Center.

Discovery, with Commander Steven W. Lindsey at the controls and five other crew members aboard, was scheduled to touch down at the Kennedy Center landing facility at 9:14 a.m. Eastern time, dropping from an altitude of 175 miles in a little over an hour.

Mission planners said, however, that the possibility of rain showers within 30 miles of the landing strip could force a wave-off. The reentry flight director, Steve Stich, said that in that case Discovery would try once more on the next orbit.

But if bad weather persists, Stich said, Discovery will stand down and try twice more Tuesday morning. Only after two more wave-offs would he order a landing at the backup site at Edwards Air Force Base in California, he said.

"We don't give probabilities for landing weather, but my experience is that it's always a challenge in Florida in July," Stich said in a televised news conference from Houston's Johnson Space Center. "My intent would be to come in tomorrow, but if the weather doesn't cooperate, I would plan to land on Tuesday."

Weather during the summer rainy season in central Florida is notoriously unpredictable. Cloud cover and thunderstorms early in the month delayed Discovery's launch for three days, and bad weather forced the orbiter to land at Edwards last year.

Stitch said Discovery has enough electrical power to remain aloft until Wednesday but will not stay up for two extra days unless there is bad weather at Kennedy and Edwards, which is highly unlikely. He said brush fires east of Los Angeles are not affecting landing conditions in California.

NASA strongly prefers to land the shuttle at Kennedy to avoid having to ferry the orbiter across the country, a time-consuming process, especially with the program expecting to fly the shuttles four or more times a year for the next four years.

This optimistic plan gained a considerable boost from Discovery's near-flawless 13-day trip to the international space station, only the second mission to fly in the 3 1/2 years since the shuttle Columbia disintegrated over Texas on reentry.

Discovery replenished the station and repaired station equipment. A key task was to test new post-Columbia safety techniques, and repeated inspections of the orbiter showed that its heat shielding had survived the rigors of launch with scarcely a blemish.

Early Sunday, shuttle communicator Steve Frick in Houston relayed the results of a final infrared scan that checked for micrometeoroid damage to the "reinforced carbon-carbon" that insulates the front surfaces of the shuttle's wings and nose cap.

"They all look pretty good," Frick told Lindsey, continuing with an updated weather report.

"Is the vehicle cleared for entry?" Lindsey asked.

"That's affirmative," Frick replied. "I am told I can use that word. You are cleared for entry."

Frick also said engineers had decided there was no threat to reentry from a puzzling leak in a fuel tank supplying one of the "auxiliary power unit," or APU, turbines for Discovery's hydraulic system. "The plan for tomorrow will be for nominal [normal] operations," he told Lindsey.

The tank, filled with 13 pounds of nitrogen and a volatile rocket fuel called hydrazine, has been losing pressure gradually since launch. Engineers are unable to tell whether the tank is leaking nitrogen, which poses no threat, or hydrazine, which could cause a fire.

Mission managers said Friday that the hydrazine would need to leak 100,000 times as fast to pose such a threat, and after testing Sunday showed that the rate of seepage had not increased, they cleared the system for use.

"Right now the leak rate is very stable," Stich said. "Should it increase, the APU has the ability to shut itself down." In that case, engineers said, the shuttle could not operate its landing gear hydraulically, but would have to blow open the doors and lower the wheels with pyrotechnic charges.