The U.S. space agency NASA is marking Saturday's 20th anniversary of the Challenger space shuttle tragedy, which took the lives of seven astronauts.
Families of the astronauts will take part in a ceremony at the Kennedy Space Center in Cape Canaveral, Florida, where Challenger was launched. Among those on board was high school teacher Christa McAuliffe.
After a successful liftoff in near freezing temperatures and clear, blue skies, Challenger exploded into a huge fireball 73 seconds into flight as people across the world watched on television. The cause of the explosion was a poorly designed seal in the shuttle's solid rocket booster.
Three years ago, the space shuttle Columbia disintegred while re-entering earth's atmosphere, killing another seven astronauts and causing the temporary grounding of the shuttle fleet.
Some information for this report was provided by AFP and AP.