Though NASA usually launches six flights a year, a fleet-wide wiring inspection and other technical problems kept the agency's only spacecraft available to put humans in orbit grounded.

Coupled with a pair of highly publicized failures in the Mars exploration program, Howard McCurdy, a professor of public affairs at American University, believes NASA faced pressure to end the year on a high note.

"People really wanted to fly, but they didn't want to fail," McCurdy said. "And of course, those are very contradictory goals."

However that pressure didn't come from Washington.

"It comes from within," McCurdy said. "It's not somebody at the top saying, 'Fly it!'"

"People always assume that government employees are responding to pressure from Congress when they do things that may not be justifiable," said Dana Rohrabacher, (R-California), House Space and Aeronautics Subcommittee chairman. "But quite often that isn't done in response to us but from pressures within the organization."

Rohrabacher said he did not believe that NASA necessarily felt the pressure in this case.

NASA officials said they were not influenced to launch by the well-publicized failures of the Mars orbiter and lander probes.

"I don't look at the Mars activities that have gone on and what you have reported in the press as any factor on the shuttle program," said Ron Dittemore, shuttle program director. "I've got to have my head in the game of launching shuttles, and doing them safely, and doing them when they're ready to fly. So I read your press reports, and I see what might have happened with the Mars programs. But that does not affect my thinking...or planning."

Time and time again, NASA had chosen to delay the mission, originally slated for October. At first, it was a host of minor technical problems. But rather than go through with the launch, Dittemore said he chose to hold until he felt it was safe to go.

The various inspections and fixes left NASA with a nearly overhauled Discovery shuttle.

"We have a vehicle that has absolutely no anomalies on it -- not a single one," said Don McMonagle, shuttle program launch integration manager. "We couldn't ask for a more perfect vehicle and a more perfect scenario to execute this mission."

Once the shuttle was ready to go, a bad weather front blocked what was thought to be the last two available launch days -- last Friday and Saturday. Mission planners set this limit because they are unwilling to have a shuttle aloft over the New Year's holiday for fears of Y2K computer glitches. The agency set a December 27 deadline for the end of the mission.

The last-chance launch date was shifted to Sunday when a NASA team evaluated the one remaining problem -- the chance that the shuttle may have to land at Edwards Air Force Base in California, rather than return directly to its Florida home.

NASA habitually builds two spare days into a mission, in case bad weather makes it impossible for the spacecraft to land at Kennedy Space Center. The scenario they had looked at: If the shuttle launched on Sunday, and if NASA had to use the extra days, and if Discovery could only land at Edwards -- then there wouldn't been enough time to bring the shuttle in before January 1. So NASA originally decided Sunday was too late, McMonagle said.

When Saturday's weather looked bad, NASA looked for ways -- and found them -- to trim the shutdown time at Edwards. And they decided to go for it.

To safely close out the shuttle, NASA must drain all of the fuel and power from the craft. The change in plans at Edwards would use a new technique to drain all of the liquid hydrogen.

"I don't have the technical expertise to determine right now whether they compromised safety by a few points in order to get the liftoff," Rohrabacher said. "All I can say is that the committee has made it very clear that NASA should hold up any launch rather than risk people's lives."

McMonagle said there was no risk to life whatsoever and that there was only "a bit of a risk" to the vehicle.

"We traded those two risks honestly: The probability of one in 200 that we would land at Edwards on the 29th, and the risk associated with landing and slightly altering our post-landing scenarios," McMonagle said. "We made a judgment call in the interest of doing the right thing to go attempt a launch with the good forecast we had in front of us, and I believe we will be successful in accomplishing this mission. You pay us to make these kinds of judgment calls and I believe we made the right one."

NASA has long prided itself as a "can-do" agency able to tackle any problem, McCurdy said. People familiar with NASA can get testy with the engineers in charge of the vehicle, even though they are aware of the complexity involved in launching astronauts into space. It happened at NASA's first piloted mission in 1961, McCurdy pointed out, when Mercury astronaut Alan Shepard, stuck waiting on the pad for hours, groused to launch control to "Light this candle!"

Whether they are conscious of it or not, NASA will present a good image at the end of the year by servicing the Hubble, McCurdy and Rohrabacher said.

"Nobody else in the world could fix this telescope," Rohrabacher said.

"Even though we want to find a replacement for the shuttle, it still gives us a greater capability than any other spacecraft and it is certainly part of America's consciousness right now."