NASA marked a trio of space tragedies with ceremonies at the Kennedy Space Center on Friday and at Arlington National Cemetery on Thursday, commemorating the astronauts who lost their lives in accidents.

Forty-five years ago, Apollo 1 astronauts Virgil "Gus" Grissom, Edward White and Roger Chaffee climbed aboard their capsule for a routine pre-launch test. A fire broke out in the cabin, dooming the astronauts. The accident, traced to a design flaw, delayed America's foray to the moon for almost two years.

Saturday marks the 26th anniversary of the Challenger disaster. Astronauts Dick Scobee, Michael Smith, Judy Resnik, Ellison Onizuka, Ronald McNair, Greg Jarvis and schoolteacher Christa McAuliffe died following the breakup of the space shuttle 73 seconds after liftoff on the cold winter morning of Jan. 28, 1986....

Tragedy struck again on Feb. 1, 2003, when the shuttle Columbia was destroyed 16 minutes before its scheduled touchdown in Florida following a 16-day research mission. The shuttle had been damaged by a piece of insulation that fell off the fuel tank during liftoff and damaged the ship's left wing....