CAPE CANAVERAL, Fla. - NASA is once again marking a series of somber anniversaries and remembering 17 astronauts who died in the three tragedies.
It has now been 35 years since space shuttle Challenger blew apart after launch, 19 years since space shuttle Columbia broke up during reentry, and 54 years since a launch pad fire killed three Apollo astronauts.
CHALLENGER: JANUARY 28, 1986
The space shuttle Challenger tragedy wasn't the first time that astronauts were killed, and it wouldn’t be the last. But it's the tragedy that most people remember so vividly; the image of the fiery explosion contrasted against the blue morning sky is burned into the memories of millions who tuned in to watch the launch.
By now, the backstory is familiar to most people. Seven astronauts were killed, including the woman who was supposed to be America's first teacher in space. Schoolchildren around the U.S. watched live as the horrific scene unfolded before their eyes.
The accident was technically caused by a rubber seal inside a booster that failed in the unusually cold Florida air, but investigators also blamed NASA for their schedule-induced 'launch fever.' It would be two and a half years before flights were ready to resume.
COLUMBIA: FEBRUARY 1, 2002
Sixteen years later, NASA's culture would again be blamed after the agency misjudged the danger posed by foam debris from the shuttle's orange external tank. A suitcase-sized piece of foam slammed into Columbia's left wing, punching a hole that allowed superhot gas to burn through the craft during reentry.
Seven astronauts were killed and debris rained down over several states. The ensuing investigation was highly critical of NASA's safety culture and ultimately led to the agency's decision to retire the space shuttle fleet.
APOLLO 1: JANUARY 27, 1967
America's first space tragedy actually happened on the ground just as the race to the moon was picking up speed. The first launch of NASA's new three-person Apollo spacecraft -- designed specifically as part of the system to land men on the moon -- was just weeks away. A seemingly routine test on the launch pad ended with a frantic cry: "There's a fire in here!"
A frayed wire caused a spark that quickly grew into a roaring fire inside the sealed spacecraft, which had been pressurized with 100-percent oxygen. The three astronauts struggled unsuccessfully to open the hatch and escape.
Several astronauts, including those who gave their lives, had been complaining about the quality of the spacecraft prior to the fire. Afterwards, the Apollo program stood down for months as systems were redesigned and spacecraft were improved.
Several other astronauts have died in the course of their training or other activities on the ground; plane crashes have killed seven astronauts and cosmonauts, including the first man in space, Yuri Gagarin. Four Soviet cosmonauts on two separate missions also died during the race to the moon due to technical failures of their spacecraft.