How do I know this, because I was home sick when this happened!

CAPE CANAVERAL, Florida (AP) -- Twenty years ago, space shuttle Challenger blew apart in jets of fire and plumes of smoke, a terrifying sight witnessed by the families of the seven astronauts and by those who came to watch the historic launch of the first teacher in space.

The disaster shattered NASA's image and the belief that spaceflight could become as routine as airplane travel. The investigation into the accident's cause revealed a space agency more concerned with schedules and public relations than safety and sound decision-making.

Seventeen years later, seven more astronauts were lost on the shuttle Columbia, leading many to conclude NASA had not learned the lessons of Challenger.

But after last summer's successful return to flight under the highest level of engineering scrutiny ever, many space watchers are more hopeful.

"Don't we all learn as we go?" said Grace Corrigan, who lost her daughter, teacher Christa McAuliffe, in the Challenger accident. "Everybody learns from their mistakes."

Joining McAuliffe on the doomed January 28, 1986 Challenger flight were commander Dick Scobee, pilot Mike Smith and astronauts Ellison Onizuka, Judy Resnik, Ron McNair and Greg Jarvis.

"It was one of those defining moments in your life that you will always remember," said Democratic Sen. Bill Nelson of Florida, who flew on the shuttle mission preceding Challenger. "Because in 1986, the space shuttle was the symbol of technological prowess of the United States and all of the sudden it's destroyed in front of everybody's eyes."

The two shuttle disasters, as well as the deaths of the Apollo 1 crew during a 1967 launch pad test, taught the space agency how to improve the herculean task of launching humans into space, NASA administrator Michael Griffin said recently.

On Thursday, NASA workers paused for their annual Day of Remembrance in honor of those lost in all three accidents. On Saturday, a ceremony remembering the Challenger accident is planned at Kennedy Space Center. (Full story)

Challenger was brought down just after liftoff by a poorly designed seal in the shuttle's solid rocket booster, which has since been redesigned and has performed without problems. It will be used on the next-generation vehicle with plans to return astronauts to the moon and later to Mars.

"We learned how to design solid rocket boosters ... with no further failures," Griffin said. "We got that from the Challenger crew, so that is part of the learning process, I'm afraid."

The Challenger disaster came in an era of tighter budgets, smaller work forces and a constant need for the space agency to justify the shuttle program that followed the heyday of the Apollo moon program. NASA had hoped sending a teacher into space to give a lesson would win back some public interest and show how routine shuttle flights could be.

The success of the Mercury, Gemini and Apollo programs had led NASA to believe that spaceflight eventually could become as commonplace as an airplane ride, said Stanley Reinartz, the former manager of the shuttle project office at the Marshall Spaceflight Center in Huntsville, Alabama. He made the decision not to take engineers' concerns about the Challenger's O-ring seals to the highest reaches of NASA management.

"Things can go wrong," Reinartz said of the decision to launch. "You don't get away from it. It's always there."

Nelson said he is confident that the current NASA leaders have learned the lessons of management hubris from their predecessors. Griffin grounded the shuttle fleet last summer after foam fell off the tank of Discovery during the first shuttle flight after Columbia. It was a chunk of foam debris that doomed Columbia by knocking a hole in its wing.

"The problem that NASA has had that caused the destruction of both space shuttles is the same ... -- arrogance in the management of NASA so that they were not listening to the engineers on the line," Nelson said.

But some critics wonder how long the 2-year-old reforms and attitude changes implemented after Columbia will last until, once again, dissenting opinion is discouraged and NASA managers override the concerns of their engineers.

In a series of telephone conference calls the night before Challenger's liftoff, engineers from NASA contractor Morton Thiokol recommended against a launch because data showed that cold temperatures compromised the O-rings' resiliency. The temperature at launch time was 36 degrees Fahrenheit (2.2 Celsius).

Under perceived pressure from NASA managers, Thiokol managers reversed themselves and went against the recommendation of their engineers not to launch, according to the investigation by a commission appointed by President Reagan.

"The presidential commission made very powerful and strong recommendations on how the system needed to be fixed," said Roger Boisjoly, a former Thiokol engineer who had opposed the Challenger launch during the conference calls. "Initially NASA installed every one of those (recommendations), but in the ensuing years proceeded to dismantle them."

Griffin said he is reminded of the early days of the nation's air transport system when scores of test pilots died in plane accidents during the early part of last century.

"The knowledge we gained was gained only through many, many losses," Griffin said. "That is the perspective through which we must look at our losses in spaceflight."