For the select few who have toiled nearly three years in the shadow of the Challenger disaster, this is the hardest time: Like expectant fathers in the waiting room, they too must nervously await the rebirth of America's space program.

Poised on the launch pad as the countdown enters its home stretch, Discovery is a monument to American ingenuity. But it's also a haunting reminder of American failure.Much is riding on the launch, which is scheduled for later this month and will end nearly a three-year drought in the space business for the United States. The integrity of NASA, the aerospace industry and people who dare to dream are at stake.

Here in Utah, the future of thousands will also ride the giant spacecraft along with the five astronauts.

"It's not another flight," said Don Lind, who flew aboard the shuttle Challenger in April 1985. "We're back in business.

"Everybody realizes that the NASA manned space reputation is on the line. If there's an accident on this shuttle flight, I would suppose the shuttle is out of business forever. This is the proof of our competence to press forward with the shuttle system. So in a sense, this flight is incredibly important," said Lind, who now teaches physics at Utah State University.

Nearly 12,000 Utahns make space their business, either through work with contractors and subcontractors or research at Utah's universities. In 1986 alone, Utah firms and universities held $316 million in prime NASA contracts for space work.

Gil Moore, a former Morton Thiokol spokesman and now a USU physics professor involved in satellite marketing, said resuming shuttle flights means "a revitalization of the interest and confidence in the program. We've had an interruption."

Discovery's launch is, to use the tired phrase of NASA and Thiokol types, a milestone: The information gathered in the $450 million redesign project has helped reaffirm engineers' design theories in creating the safest space vessel possible.

Allan McDonald, the Thiokol engineer who made headlines for opposing the ill-fated Challenger launch, said after the final test firing of the redesigned rocket that information gained in the past 32 months far exceeds what engineers knew when the

irst shuttle lifted off in 1981.

An Aug. 18 test of a rocket hammered with 14 built-in flaws to verify engineers' predictions and precautions were correct was the final hurdle Morton Thiokol had to pass before certifying the boosters were ready for flight, assuring there would be no repeat of Challenger.

Challenger exploded into a ball of fire, killing its seven-member crew, when a flawed O-ring seal connecting two segments on the right-side booster rocket allowed hot gases to leak through, igniting the spacecraft's huge external fuel tank. The August test at Thiokol's Wasatch Operations facility tried to mimic as close as possible what may have occurred that fateful Jan. 28, 1986.

Data from the five full-scale tests, 20 separate small-scale tests and development of sophisticated measuring devices have "confirmed a lot of analytical models that have been developed in the past 21/2 years that weren't available 10 years ago," McDonald said.

"And those tools are very powerful with computers we have now, and our understanding of this joint is many orders of magnitude better than it ever was," he said. "I think we now have a data base that's confirmed our understanding at a very high level.

"I feel very comfortable that this rocket motor is not only the most reliable rocket motor ever built by anyone in the industry, but it is a rocket motor that is going to be reliable for a long time to come because we have built-in such a robust design that we can accommodate things that I can't anticipate will ever happen and it will fly OK."

The successful launch of Discovery also will regain some of the lost pride as well as some of the lost ground resulting from the involuntary intermission.

deal" to get the United States back into space, said Lind.

"Over the years, we Americans have had a lot of feelings of inferiority, particularly back in the '60s. And the space program was the shining exception to that.

"I don't think we're quite as introspect or paranoid or whatever you want to call it as we were in the '60s," Lind said. "But the space program is a point of national pride and right now we are in deep trouble."

The native Utahn pointed out the progress the Soviets and Europeans have made in space stations and satellite launches, while the shuttle fleet has been grounded.

"Now I don't know what fraction of the American public feels a sort of a national embarrassment that our space program is in such serious trouble, but whatever that fraction is, those people are going to feel a lot better when the shuttle starts flying again."

The grounding of the shuttle fleet has put numerous scientific and defense projects on hold. Taking care of the back log will mean piling experiments on each shuttle flight - now estimated to be as frequent as one a month.

"The meter's running and we're using up dollars with the things sitting on the shelf waiting to fly," said John Taylor, a spokesman at NASA's Marshall Space Flight Center in Huntsville, Ala.

The five-man crew of Discovery will launch a satellite which, combined with a similar satellite already in orbit, will provide high-capacity communications and data links between Earth and the shuttle. An identical satellite was lost in the Challenger explosion.

The secondary payload includes experiments on protein crystal growth, white blood cells, infrared communications and lightning.

More than a dozen experiments at USU are in line to fly aboard future shuttles, said Lind, who is waiting for an experiment he put into space in 1984 to come back to Earth. The experiment on a satellite was supposed to have come back to Earth in 1984, but retrieval of the satellite was bumped back to 1985 and then 1986.

"So here I've got an experiment that could be very scientifically significant that has been in orbit 41/2 years longer than it should have been. I'm hoping that the shuttle gets operational pretty quick so that they can go back and get that satellite so I can get my scientific data before the satellite falls on somebody's head."

While no Utah universities or businesses have experiments on Discovery, the state has a healthy history in space experimentation. USU has flown more professional experiments on the shuttle than any other university.

"Utah is heavily involved in experimentation in space," said Moore, who bought the first getaway special, a package in which experiments can be placed to fly aboard the shuttle, from NASA in 1976 and donated it to USU. Moore also worked with Weber State College on NUSAT (Northern Utah Satellite) - the first student-built satellite. A total of 26 getaway specials from USU have flown aboard shuttles.

"And so the university's activities in the shuttle program have suffered a significant hiatus. And now the resumption of the launch program will allow resumption of that very substantial involvement in space experimentation," Moore said.

While NASA prepares to fire up Discovery, now sitting on launch pad 39B at the Kennedy Space Center in Florida, Morton Thiokol is preparing to build another 11 sets of booster rockets at its Brigham City facility. No. 12 already is down at Cape Canaveral for the next shuttle flight, and the thirteenth is being assembled in Florida.

Estimates by the Utah Economic & Business Research Bureau show one in every seven jobs in the state is dependent on federal defense and space contracts, and $1 of every $5 put into the Utah economy comes from such contracts. Aerospace is Utah's second-largest employer, according to bureau figures.

Dave Ewing, Morton Thiokol's deputy director of program involvement, said NASA is preparing to release a proposal to build another 70 sets of redesigned solid rocket motors.

"I anticipate that we'll stabilize at about what our current work force has been. We have been producing at about the peak rate that the schedule in the future calls for, making all these qualification motors, and motors shipped to the Cape for the first, second and third flights. The rate has been quite high," Ewing said.

Workers at Morton Thiokol's Wasatch Operations facility now are preparing hardware for the fourth and fifth booster sets, Ewing said.

"We've been building our confidence and feeling a whole lot better with each test, and this will just be a tremendous relief and a feeling of accomplishment for us when we fly successfully again."

NASA has put out its final call for bids on the second-generation shuttle booster rockets that will be used once NASA's current contract with Morton Thiokol has concluded.

NASA wants a government-owned, contractor-operated facility built in Mississippi so it can have a tighter reign on what is built for the space program.

Morton Thiokol opted not to compete for the contract, while Utah's Hercules Bacchus Works in Magna has teamed up with Atlantic Research to go after the bid.

"Our redesigned solid rocket motor is going to continue to be used for a good number of years and until that advanced solid rocket motor (ASRM) proves itself flight worthy," Ewing said.

"We kind of have a feeling here that if we make this redesigned solid rocket motor the very best we can, it's going to prove out to be the most reliable solid rocket motor ever used," Ewing said. "And I believe that NASA's motivation for wanting an ASRM will wane.

"Also it's my own personal opinion that the final cost for the government-owned, contractor-operator facility hasn't been seen yet. When it is, and when Congress has to ante up the money, and if we're at that time flying very successfully and have a highly reliable motor, I don't know why Congress would be motivated to continue to pay the bill."

The tab for the government-owned facility, including building costs, is estimated at more than $1 billion. The final proposals from contractors are due at the end of October, and NASA will announce a winner early next year.

"We intend to be here a long time. We're just on the threshold of space," with proposals for an unmanned shuttle, advanced launch system, space launch vehicles and improved Titan missiles, Ewing said. "And we intend to be part of that."

A study by Northern Illinois University researchers has found anticipation for Discovery's launch has increased, not waned, in the nearly three years since the Challenger blew up.

"The American people underwent a radical change in attitude. Before Challenger, they had grown blase about the program's successes. Afterward, there was a surge of support so strong that it made me question our data," said Jon Miller, director of the Public Opinion Laboratory at NIU-De Kalb.

"The Challenger tragedy really made the public focus on the space issue," Miller said. His laboratory is widely regarded as the nation's leading center for the study of attitudes toward space.

"Since 1986, the issue has crystallized," he said. "The space shuttle symbolizes national pride."

Results of the ongoing three-year study show nine of 10 Americans believe regular manned shuttle flights will resume, said Miller, who has surveyed public opinion since 1979 for the National Science Foundation.

Along with the enthusiasm comes sophistication. People expect accidents in the future and have a more realistic assessment of space exploration, Miller said.

Says Lind: "In the golden days of the space program, back in Mercury and Gemini, these guys were national heroes. And rightly so. Nowadays they're just truck drivers at high altitudes."

He said the accident also reaffirmed the reality of the non-routine nature of space flight. "So every time you climb aboard you're putting your life and your equipment on the line that it's gotta work. So I think that blase attitude, well, that's gone I think forever. It's more realistic."

Along with the changing American attitude has come a deepened respect for Morton Thiokol and NASA, which took a beating from armchair engineers after the Challenger disaster.

"My sense is for a while Morton Thiokol was kind of a pariah, and I think over the period of the last year we've proven that we know what we're doing, that we have redesigned the motor properly and it is reliable. And I think the public mood has changed somewhat. And I sense that the public is behind us again," Ewing said.

But whether the public's money is behind space exploration depends on Congress.

"Everything hinges on those con-gressional appropriation committees," Lind said. "This mission is going to be wonderfully successful."

It needs to be.

"The budget is not going to go up one penny if the flight is successful. We are so wrapped around the axle right now trying to run the federal budget that NASA can get whatever it can haggle for. If this flight blows up, the budget will go down. If the flight is successful, the best they can do is hold their own," Lind said.

"But Congress isn't going to jump up and down and say, `Oh goodie, goodie, goodie. Let's give 'em an extra 200 million.' That just absolutely is not realistic."

Right now, however, the dreamers would just settle for jumping back into space.