The last Thursday in January is considered a day of remembrance at NASA, honoring those astronauts who died in the line of duty. They include the crews of Apollo 1,STS 51-L Challenger, and STS-107 Columbia.

On Jan. 27, 1967, during a plugs out pad test of the Apollo 1 capsule, a fire broke out insider the command module. The fire, likely started by a sparked in some accidentally stripped wiring, was exacerbated by the pressurized pure oxygen atmosphere inside the capsule and the presence of flammable material. The astronauts, Gus Grissom, Ed White, and Roger Chaffee, died in seconds from the smoke, toxic fumes, and intense heat of the fire. The hatch, which would have opened inward, could not have been opened against the cabin pressure.

The Apollo Fire, ironically, very likely saved John Kennedy's goal of landing a man on the moon. The fire forced a complete redesign of the Apollo command module that made flying the space craft by degrees of magnitude safer and likely prevented an even worse catastrophe from happening during a space mission.

On Jan. 28, 1986, the Challenger shuttle exploded 72 seconds after liftoff, killing her crew, including teacher in space Christa McAuliffe. The accident was caused by the leakage of super hot gasses through a faulty O ring in one of the solid rocket boosters, causing the main fuel tank to ignite and break up. The crew cabin of the space shuttle orbiter continued to rise for a moment, before plummeting into the Atlantic Ocean.

NASA spent two and a half years redesigning the space shuttle system to prevent a reoccurrence of the accident. The next space shuttle mission, STS 26 Columbia, launched on a successful mission in September 1988.

On Feb. 1, 2004, the Columbia shuttle broke apart in the skies over Texas, pieces falling scattered over a wide area of the United States. As seen from the ground, the death of the Columbia and her crew seemed like the passage of an angry comet, streaking across the morning sky.

Columbia was likely doomed from the first. It was determined that insulation from the external tank had broken off and had impacted the orbiter during launch, striking some of the reinforced carbon panels along the left wing of the orbiter. The heat of reentry burned through the orbiter, causing it to break apart as it soared through the Earth's atmosphere.

Another extensive redesign and change in flight procedures was undertaken before the remaining space shuttle flights were allowed to proceed. The Columbia accident galvanized a move to begin anew human exploration beyond low Earth orbit. President George W. Bush announced a program to do just that less than a year after the Columbia accident. However, his successor, Barack Obama, canceled that program about six years later.