Twenty-five years and a generation later, members and supporters of the American space program are remembering the seven crew who perished aboard the space shuttle Challenger.

Families and NASA officials gathered at an outdoor memorial at Florida's Kennedy Space Center on Friday morning, to mark the quarter-century that's passed since the shuttle Challenger exploded, taking the lives of its crew and casting doubt on what had, until then, appeared to be an unflaggingly safe space program.

After launching late in the morning of Jan. 28, 1986, Challenger was bound for six days in space when it exploded just 73 seconds into its flight.

As the world watched events unfold live on broadcast television, the shuttle exploded in a spectacular, careening fireball.

The crew compartment emerged from the blast intact to soar almost 5 kilometres more before plummeting Earthward in a free fall that lasted more than two minutes.

With no parachute, escape system or even protective clothing for the crew, all seven aboard -- including the first schoolteacher and ordinary citizen launched into space, Christa McAuliffe -- had no hope.

Cmdr. Dick Scobee, pilot Michael Smith, payload specialist Gregory Jarvis and mission specialists Judith Resnik, Ellison Onizuka and Ronald McNair were also killed as the eyes of the world watched in shocked disbelief.

Looking back on the events of that day, Canada AM space educator Randy Attwood laments the sense of routine that pervaded NASA's attitude toward shuttle flights at the time.

"It's sad when you look back to know that the engineers knew about the problem that ultimately brought Challenger down," Attwood said in an interview with CTV's Canada AM on Friday, recalling the combination of freezing launch weather and a disintegrating booster rocket O-ring seal that were eventually blamed for the disaster.

"It reminds us that even though it looks like it's straightforward going into space on the space shuttle, it is risky business."

Before the ill-fated Challenger launch, NASA had flown its shuttles into space two dozen times without incident. But that year, delays were frustrating the space agency's goal of launching the shuttle fifteen times in twelve months.

Instead, after the deadly disaster, the program wound up grounded for more than two years.

Seventeen years after the Challenger explosion, almost to the day, seven more astronauts died when a chunk of fuel-tank foam led to the shuttle Columbia ripping apart as it descended to Earth at the end of its mission.

Now, the shuttle fleet is grounded once more as engineers struggle to correct fuel tank cracking they fear could lead to another catastrophic malfunction.

The shuttle Discovery is expected to launch by the end of February, with Endeavour slated to follow in April. Then, Atlantis is slated to mark the official end of the 30-year shuttle program when it's launched into space late in the summer.

Although that final flight will mean NASA no longer has a means of launching its own astronauts into orbit, the agency has yet to announce a replacement. Undaunted, U.S. President Barack Obama announced last spring that the U.S. hopes to send humans to Mars and back in the next twenty years.

Canada's space program, which has long-relied on NASA for carriage into orbit, is planning to maintain its own commitments in space including the upcoming mission of veteran astronaut Chris Hadfield to serve as commander of the International Space Station for three months in 2013.