Twenty-five years ago, seven astronauts died aboard space shuttle Challenger when it exploded shortly after lift-off. NASA officials, families and former astronauts gathered for an outdoor memorial at Florida's Kennedy Space Center to mark the sombre anniversary.

Challenger exploded just 73 seconds into its flight, killing all seven people on board. NASA is shutting down the 30-year-old shuttle program due to high operating costs. It also wants to free up funds to start developing a new space launch system. It would carry people and cargo to asteroids and other destinations beyond the station's 350 kilometer high orbit. NASA's Associate Director spoke at the ceremony of the need to honor the Challenger crew by re-doubling exploration efforts.

William Gurstenmaier, NASA Associate Director said "We, who remain on the ground and asked them to fly, failed them that day. As we would fail the crew of Columbia 17 years later and as we failed the crew of Apollo One 19 years before. The only possible compensation that we can offer is our renewed devotion to the jobs we've been asked to do by the nation to explore the universe that surrounds us. We seek to answer the most difficult questions imaginable and formulate new questions."