Never has there been a shuttle mission like the one set to lift off Wednesday. Not during those nervous days of the very first flight, when the shuttle seemed a fantastic thing ripped from the pages of science fiction. Not during the return to flight after Challenger, when the future of America's human spaceflight program hung on every bolt and O-ring.
This is something new - even for the agency that landed astronauts on the moon. There will be more than 100 cameras on the ground, in the air, and on the shuttle itself - all ready to image any errant ice chip, and promising so much data that it might take a week to sift through them. There is the new laser-tipped boom to inspect the shuttle's brittle undercarriage, the new white-knuckle maneuvers to let the space station crew inspect the vehicle - and the new emergency plans in case they find something.
It is a new reality that in some ways harks back to America's moon shots, with NASA looking at its fleet of spaceships for what they are - experimental machines more like the temperamental test planes of Chuck Yeager than the clockwork space ferries of Arthur C. Clarke - and planning accordingly. Yet this also marks the beginning of a dangerous and drawn-out coda for the shuttle era.
Only the space shuttle can fully service the still-unfinished International Space Station, which has cost Americans more than $100 billion. That leaves NASA with little choice but to try to wring five more years from an aging shuttle fleet, and with President Bush's grander plans for the moon and Mars still ahead, the agency can't afford another failure. The way forward, this mission suggests, is very carefully.
"Every flight is a test flight," says John Logsdon, a member of the Columbia Accident Investigation Board (CAIB). "If NASA can't maintain a strong focus on shuttle safety over five years, then shame on them."
In the past, a focus on safety has proved difficult. Shortly after the shuttle's first test flight in 1980 - and then again when the shuttles returned to service the after the Challenger accident in 1986 - the initial vigilance waned. The fact that the fuel tank shed foam during liftoff was normal; divots in the heat shield became ordinary. In fact, the heat-resistant tiles have been damaged an estimated 15,000 times over the shuttles' life span, and 10-inch gashes occur during 1 in 5 flights.
It was one such gash in the leading edge of Columbia's left wing that caused it to burn up as it reentered Earth's atmosphere on Feb. 1, 2003, according to the CAIB. Some 2-1/2 years and $1 billion later, NASA says it has devised solutions to ensure a safe return to space. [Editor's note: The original version misdated the Columbia accident.]
Others aren't so sure. Most notably, the shuttle is returning to flight without fulfilling all the recommendations laid out by CAIB. The massive orange fuel tank has been redesigned in order to minimize the amount of foam that could fall off and strike the shuttle's thermal shield during liftoff. But NASA scientists refuse to rule out the possibility of what they call the "golden BB" - a tiny piece of ice-encrusted foam that hits in just the right place to cause catastrophic damage.
Moreover, NASA engineers have struggled to devise new patches that astronauts could apply to damaged tiles during spacewalks. The astronauts themselves have professed doubts as to whether the ones they have now would work.
Yet Dr. Logsdon and others say NASA has done all it can. Engineers could spend another 2-1/2 years refining the shuttle, but it would still have flaws. The shuttles' failure rate of two in 113 missions, many say, is probably a fair measure of the vehicle's reliability.
The odds for failure inherent in the Apollo missions were 30 percent, notes Howard McCurdy, a NASA historian. But the program never lost an astronaut because it always imagined the worst - and prepared for it. "If you accept what the shuttle is, then it is as close as it's going to be to be ready to fly," he says.
The attitude seems to be returning to NASA. For launch, the agency has assembled the largest array of cameras ever to monitor an ascent. Once in orbit, Discovery will deploy its new 50-foot-long boom, which holds a laser camera designed to look for holes in the shuttle's thermal skin. Then, as Discovery approaches the space station, Commander Eileen Collins will perform a roll - temporarily losing sight of the outpost - so that its crew can see the tiles.
If they find major damage, NASA might have the seven shuttle astronauts use the Space Station as a lifeboat until a new shuttle arrives.
As before, this renewed vigilance could vanish in a sigh of relief after a successful flight. But analysts see reason for hope in NASA's new administrator and its new mandate. Never before has NASA had an administrator like Michael Griffin, a scientist with six postgraduate degrees. In a bureaucracy that has been repeatedly accused of neglecting to ask the tough questions, Dr. Griffin is doing much of the asking.
But the end of the shuttle program itself is also a motivation. In all likelihood, the shuttle will need to fly no more than two dozen missions to finish the Space Station. That should help shuttle managers keep their focus, says McCurdy. "What we're seeing here is not the beginning of a new beginning, but the beginning of the end of an era."