CAPE CANAVERAL, Fla. - Like other astronauts in the early 1980s, Bryan O'Connor was amazed when NASA declared the space shuttle operational and ready for passengers and payloads after just four test flights.
''Don't pay any attention to it,'' a senior shuttle pilot advised him. ''It will take 100 flights to really work out all the bugs and understand what we have with this vehicle.''
Well, flight No. 100 is finally here: Discovery and a crew of seven share the honors with a liftoff this week. Yet the space shuttle is still anything but routine.
''I don't think anybody would say that it meets the safety criteria that would be suitable for public transportation,'' says O'Connor, who's now a safety expert in the corporate world. But he adds: ''It's an incredible machine.''
By NASA's own reckoning, space shuttles should have been peeling into orbit 60 times a year by 1985, a dizzying pace that would have racked up 1,000 flights by now. But the shuttles proved to be extraordinarily complicated and required more preparation for flight than officials envisioned.
So knock off a zero and here you are.
As it turns out, flight No. 100 falls just six months short of the 20th anniversary of No. 1.
''What was always crazy about the shuttle was who was going to fly on all these flights? What was going to go up there?'' says Alex Roland, a former NASA historian who teaches at Duke University.
The answer - 260 people and nearly 3 million pounds of cargo flown through last month's mission. Of the more than 850 payloads, more than 60 have been deployed in orbit.
Headliners include John Glenn, the Hubble Space Telescope and the Chandra X-ray Observatory, as well as probes to study Jupiter, Venus and the sun.
''It was going to operate so efficiently, it was going to make money and pay off its development cost,'' Roland said. ''And, of course, it's been a horrendous money loser all along.''
The cost - close to $1 billion per mission by some estimates.
Roland takes little solace in the fact that on its 100th journey the space shuttle is doing what it was designed for back in the 1970s - flying to a space station.
''The space station is going to make the shuttle look like a good deal,'' he warns.
Even though the 100th flight is a milestone, at least symbolically, NASA isn't making a big deal out of it. Neither are the astronauts who will lift off aboard Discovery on Thursday night. They're more interested in their tough space station-construction job.
This will be the first time in two years that NASA launches major pieces of the international space station, in this case a boxy girder and a docking port. The last three trips were essentially supply runs.
''If there's any significance to the 100th flight, that's fine,'' says astronaut Bill McArthur, who will make two spacewalks to wire up the new station parts. ''But it really implies nothing special about us or special about the mission.''
The mission was delayed two years because of space station snags in Russia. It would have been flight No. 99, in fact, if NASA hadn't stuck in an extra station visit by Atlantis in September.
Discovery's pilot, Air Force Lt. Col. Pamela Melroy, says 100 flights represents a lot of days in orbit - 868 days counting the upcoming 11-day mission.
''But when I look at it as a test pilot,'' she says, ''I realize that we had many more than 100 takeoffs and landings in the C-17 less than six months into a four-year test program. We are still in the experimental phase with takeoffs and landings.''
Only one mission - the 25th - has ended in disaster. The accident on Jan. 28, 1986, destroyed Challenger and killed all seven people on board.
NASA's latest statistics put the odds of catastrophe at 1-in-400-plus, thanks to improvements in the space shuttle and risk assessment.
With more than 1 million parts in each of NASA's four space shuttles, experts consider it a feat that 98 launches and landings have ended safely.
NASA envisions flying the space shuttle for at least another 10 years. Each ship was built for 100 missions; Discovery leads the pack with 27.
''They're working on designing a replacement for it and I wish them luck,'' says astronaut Terrence Wilcutt, who commanded flight No. 99. ''We're expensive to operate. But if you want a lot of capability and flexibility, there's nothing that beats the shuttle right now.''
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