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ATLANTA (CNN) -- What a difference 15 years can make.
On this week in 1986, the space shuttle Challenger stood erect on launch pad 39B -- poised for a disaster many engineers inside the program were all but certain would happen.
This week, the space shuttle Atlantis is on her way back to the Vehicle Assembly Building, so that workers can look for a problem that may not exist -- with a potential for risk that is essentially immeasurable because it is so minute.
On this week in 1986, launch managers acted like riverboat gamblers. They convinced themselves luck would be a lady -- and that the odds of rolling snake-eyes were acceptable -- when the dice were loaded against them.
This week, the shuttle management team acted more like flinty loan officers wearing green eye shades. They carefully crunched the numbers, saw a good rate of return and plenty of security -- yet still said "no."
On this week in 1986, the steely eyed rocket scientists from Von Braun's vaunted Marshall Space Flight Center in Alabama threw caution to the frigid January wind, pushing hard to light Challenger's candles, even though they knew the score.
This week, the Marshall team led the charge to delay the launch and roll Atlantis back, even though, once again, they knew the score.
On this week in 1986, NASA was desperately trying fill an empty promise by proving the shuttle fleet would be something it could never be: a fully operational, commercially viable space workhorse.
This week, NASA knows its shuttle fleet has nothing to prove -- and everything to lose -- each time the Solid Rocket Boosters light up.
Fifteen years ago, the space agency that put men on the moon was beset with an epidemic of "go fever."
The P-C era
Today, the man in charge of the $3 billion shuttle program says he guards against "go fever" as if it were a plague.
His name is Ron Dittemore, and during a conference call with a cadre of reporters on the space beat the other day, he offered some insights into NASA's "P-C" thinking (that's Post-Challenger).
Once again, the questions and concern focus on some of the many miles of wiring that interlace the orbiter, its fuel tank and solid rocket boosters.
The problem came to light during Endeavour's ride "uphill" in the penultimate month of the last millennium. A wire that transmits the "fire" command to a crucial pyrotechnic bolt attaching the solid rocket booster to the fuel tank failed. Not long after the bobbing booster was fished out of the Atlantic, a team of troubleshooters determined the wire broke away from a connector.
Had that bolt failed to go up smoke, Endeavour surely would have. A stuck solid rocket booster is, in NASA vernacular, a "Criticality-One" failure -- meaning catastrophic loss of the vehicle and crew.
Fortunately, the wire in question is classified "Crit-One-R" (meaning it has a redundant backup). The backup saved the day -- just as it did in July 1999 when a short circuit knocked out some engine controllers six seconds after Columbia lurched off the pad.
With all this in mind, the Pad Rats at launch complex 39-A made their way to the 10 ordnance wires in question on Atlantis' stack as it sat on the pad. They used a portable X-ray device to give the cables the superman treatment.
And they performed a "WIGGLE" test. (I know you will find this hard to believe, but that is NOT an acronym for Wire Integration Gross Gyration Looseness Exam -- it's just a plain old wiggle test.) In any case, the wires all checked out -- and on went the flow toward a January 19 launch.
But wait, there is more. As a further precaution, United Space Alliance technicians started pawing through the entire inventory of watertight reusable wires used to connect boosters and mother ship. After X-raying and wiggling 194 cables (which adds up to 6,056 meetings of copper and connecting pins), they found four loose wires that perform crucial command, control and pyrotechnic functions. Each is considered "Crit-One-R" -- meaning a cable and its twin would have to both fail to make for a really Bad Day.
There is no simple way to know for sure if Atlantis has some bad wires like those that flunked the inventory inspection, because they cannot be reached until the shuttle stack is enshrouded in scaffolding inside a "High-Bay" three slow miles down the crawler road from the pad. The round-trip to the Vehicle Assembly Building means a minimum three-week hit to the schedule.
And then there are the odds. The statisticians on the shuttle team sharpened their pencils and came up with the odds of a Bad Day.
"Based on statistics alone, you might be comfortable proceeding with flight," said shuttle chief Dittemore, "and there was a number of folks that felt comfortable with just a statistical analysis."
You will have to do the math. My history-major arithmetic skills -- and my Palm Pilot calculator -- are failing me. But four failures in 6,056 connections -- plus the fact all the cables have a redundant twin ... well ... equals a snowball's chance in hell of a "Crit-One" failure.
In any case, Dittemore isn't sharing the odds with us because, he says, they are "irrelevant."
"In this case, just to do a mathematical exercise is not justification to proceed. The hardware was telling us something," he says. "We had four failures that we discovered in our testing -- and we don't quite understand yet why -- and we ought to listen to what the hardware is trying to tell us."
This time the shuttle chief ignored the math -- and that is a good thing. We can only hope NASA is still "listening to the hardware" 15 years from now.
CNN Space Correspondent Miles O'Brien is a regular columnist for CNN.com.
Challenger anniversary evokes painful memories, hopeful future