The national memorial to lost members of the NASA family is etched with the names of 24 people who perished during missions or in training since the American space effort began.

"President John F. Kennedy characterized this as the most hazardous, dangerous and the greatest adventure on which man has ever embarked," said Bob Cabana, NASA Kennedy Space Center's director and a former astronaut. "But it's not an adventure without risk. The explorers throughout history have put themselves at risk for the never-ending quest for knowledge that drives us all."

Surrounded by former astronauts, NASA workers and space enthusiasts, Cabana spoke of the rewards that have come from the sacrifice of those memorialized on the monument.

"We've had our setbacks over the years, but we've always come back stronger, rededicating ourselves to achieving our goal in the safest manner possible," he said.

The Astronauts Memorial Foundation, a not-for-profit organization that funds math and science scholarships, built the memorial in 1991. It has since been designated by Congress as a national memorial.

Cabana was joined in the wreath-laying by Janet Petro, Kennedy's deputy director, and Mark Nappi, United Space Alliance vice president for Launch and Recovery Systems.

The crew members who died in the Apollo 1 fire in 1967, the Challenger explosion in 1986 and Columbia's break-up during re-entry in 2003, are included on the memorial. All three accidents occurred during the last week of January or early February of their respective years.

Others memorialized include test pilots for the X-15 and F-104, as well as four astronauts who were killed while flying T-38s. Another died in a commercial plane crash while on NASA business.

Cabana, who called the astronauts "some of the finest people I've ever had the pleasure of knowing," said the most fitting tribute to their sacrifice is to continue their goals of space exploration safely.

"So as we pause today to remember the sacrifice of those on this mirror, let's rededicate ourselves to safely achieving our goals as we transition to a new era of space exploration," he said. "This is an exciting time and we honor those who have gone before us by continuing our quest for knowledge in this greatest adventure of all time."