For seven families, today is an especially tough day.
It's the first anniversary of the destruction of space shuttle "Columbia" during re-entry to earth's atmosphere.
All seven astronauts on board were killed, including Laurel Clark, a native of Racine, Wisconsin.
NASA workers at Houston's Johnson Space Center held a memorial Friday.
It was determined that insulation from the big center fuel tank struck and damaged the leading edge of the Shuttle's wing during launch.
NASA's three remaining space shuttles can't return to flight until a slew of safety improvements are made.
It's hoped that can happen by September but may slip into next year.
Fifteen of 29 safety recommendations must be in place before the program can fly again.