Shuttle Ready to Go; Officials Scan Weather

Invoking a sense of deja vu after last Friday’s scrubbed launch attempt 31 seconds before liftoff, NASA officials said Wednesday that all problems had been corrected on the orbiter Atlantis and that it is ready for launch this morning at 10:48 a.m. PDT.

“Here we are again and we are ready to fly again,” said NASA’s newly nominated head, Rear Adm. Richard H. Truly.

NASA engineers will have a 64-minute “window” in which to launch Atlantis, which is carrying the $325-million Magellan probe that is designed to map the surface of Venus with radar. That is more than twice the 23-minute window that was available last Friday.

But meteorologists said that there is a 40% chance the launch will be scrubbed because of weather constraints. The potential threats to the mission include a chance of low-level clouds that would impede landing of the orbiter at Kennedy if the mission were aborted after liftoff, a possibility of prohibitive crosswinds at the Kennedy landing site and a slight chance of rain showers that would block the launch.

Poor Weather

If the launch is scrubbed today, said Capt. Thomas Strange, an Air Force meteorologist, the chance that weather would block a launch on Friday is also about 40%. The possibility of poor weather rises to 50% on Saturday and 70% on Sunday.

Last Friday’s attempted launch was scrubbed when computers detected a power surge in a pump that cools one of the shuttle’s three main engines before launch. NASA engineers replaced the pump this week, but a close inspection showed that it had not been damaged, according to Arnold D. Aldrich, director of the National Space Transportation System.

Technicians found metal particles and shavings, ranging in size from 10 thousandths of an inch to 40 thousandths of an inch, in the pump, but “no signs of interior scraping or wear,” Aldrich said.

He speculated that, in an “extremely unlikely event,” one of the metal shavings short-circuited two electrical leads, blowing a circuit breaker. The resulting power surge apparently vaporized the piece of metal (which was probably solder), and the pump would have been functional if engineers could have reset the circuit breaker, he said.

Engineers this week also replaced a 4-inch-wide liquid hydrogen line through which the super-cold fuel is returned to the shuttle’s external fuel tank after it is used to cool the engines. Observations of videotapes taken after the scrubbed launch suggested that the line had developed a leak in its external covering, allowing air to leak into the liquid-argon insulating line surrounding the hydrogen line.

But inspection of the line showed no leak. Further studies suggested that a cavity in the solid insulation of the line had allowed air to condense while hydrogen was flowing through the line. When the cooling pump shut down, the line warmed up, evaporating the air and creating the visible plume that technicians observed.

Neither problem endangered the shuttle or the astronauts, Aldrich said.

The five crew members--commander David M. Walker, pilot Ronald J. Grabe and mission specialists Norman E. Thagard, Mary L. Cleave and Mark C. Lee--returned to the space center from Houston on Tuesday. On Wednesday, they were reported to be flying T-38 trainers for relaxation.

NASA has until May 28 to launch the Magellan probe, the first interplanetary probe the United States has launched in 11 years and the first ever launched by the Shuttle. If it is not launched by then, the agency will have to wait two years for Earth and Venus to again be in the proper alignment for a minimum energy trajectory.