Discovery Set To Liftoff Sunday Night

Sunday, December 19th 1999, 12:00 am

By: News On 6

After nine frustrating delays, NASA decided Sunday to make one last attempt to launch space shuttle Discovery this year on a mission to rescue the Hubble Space Telescope. Shuttle managers gave the go-ahead Sunday morning after being informed that good weather was expected for the 7:50 p.m. liftoff.

Soon afterward, technicians began filling Discovery's huge externa tank with more than 500,000 gallons of fuel. Forecasters put the odds of favorable conditions at 80 percent, a considerable improvement over the past few days.

The sun peeked from behind clouds Sunday morning after two solid days of rain. For weeks, NASA had said that Saturday would be its last chance to launch Discovery this year because of the impending New Year and potential Y2K problems. But managers changed their minds following Friday night's launch delay and said they would consider a Sunday run if the team wasn't too tired. They also wanted to make sure the team could handle a touchdown on Dec. 27 as well as a landing one or two days beyond that in case of bad weather.

Officials said they worked out a plan to accommodate all landing options, including a possible detour to California if Florida's weather is bad.

"The tension level is inherent with any sort of launch, but there's no added pressure in this one," said NASA spokesman EdCampion.

NASA has had a particularly trying year, and not just in the shuttle program. Two Mars spacecraft were lost, and the international space station remained stalled. What's more, the Hubble quit working in November when too many gyroscopes broke. That's why it's so important for Discovery's seven astronauts to get to Hubble as soon as possible. They plan to replace all six gyroscopes on Hubble and install a new computer, data recorder and other gear.

The mission had been scheduled for October, but was postponed first by shuttle wiring damage, then a contaminated engine and a dented fuel pipe. Last-minute concerns over welds on critical fuel lines added to the delay. If Discovery finally takes off Sunday, it will be only the third shuttle mission this year, NASA's worst flight rate in a decade.