The widow of Challenger's commander laid a wreath of roses and carnations at a memorial honoring fallen astronauts Saturday, the 20th anniversary of the day the space shuttle lifted off from a launch pad a few miles away and blew apart 73 seconds later.

June Scobee Rodgers, whose husband Dick Scobee was the shuttle's commander, recalled waiting for the launch that chilly morning with other family members of the crew, including 12 children.

"Our lives were shattered, but over the years that followed the families persevered with tremendous success," Rodgers said. "I believe those parents launched aboard Challenger would be proud of their children."

Seven astronauts died in the explosion, and the images of the shuttle bursting apart were replayed over and over to a shocked nation.

On Saturday, 250 people joined a ceremony at Kennedy Space Center to honor Scobee, pilot Mike Smith, astronauts Ellison Onizuka, Judy Resnik, Ron McNair and Greg Jarvis, and Christa McAuliffe, who was supposed to be the first teacher in space.

Rodgers, along with NASA associate administrator Bill Gerstenmaier, laid the wreath at the base of the Space Mirror Memorial, a tall granite-finished wall engraved with the names of the Challenger astronauts, the seven astronauts killed when space shuttle Columbia disintegrated over Texas in 2003 and the three Apollo 1 astronauts killed in a fire during a 1967 launch pad test.

The audience included some relatives of the Columbia and Apollo 1 crews, as well as the widows of Challenger astronauts Smith and Onizuka. Supporters stood in line to lay flowers at the side of the monument.

"I have lived around the space program my whole life and it's a fitting tribute for those who made the ultimate sacrifice," said Susan Valek, who works for a Kennedy Space Center contractor.

The investigation into the Challenger accident revealed a space agency more concerned with schedules and public relations than with safety and sound decision-making.

The explosion eventually was blamed on a poorly designed gasket in one of the shuttle's solid fuel boosters which hardened in cold weather. The temperature at Challenger's liftoff was 36 degrees. Engineers for a NASA contractor had protested launching at that temperature, but they were overruled by their managers under perceived pressure from the space agency.

"It is our responsibility, individually and collectively, to make good decisions," Gerstenmaier told the audience. "As engineers, the machines we build can do great things but can also cause great harm."

Rodgers said the Challenger accident hadn't changed her opinion about the importance of space exploration.

"Without risk, there's no discovery, there's no new knowledge, there's no bold adventure," Rodgers said. "The greatest risk is to take no risk."