This week is an incredibly tough week for NASA. All three of the space agency's major spacecraft disasters — the Apollo 1 fire and the losses of the Challenger and Columbia Space Shuttles — occurred around this time at different points in history. NASA has made today its official Day of Remembrance to commemorate the three tragedies, but today holds some added weight as it is the 30-year anniversary of the Challenger explosion.

On January 28th, 1986, the Challenger Space Shuttle broke apart just 73 seconds after taking off from Cape Canaveral, Florida. The mission, known as STS-51-L, was meant to be the tenth flight of the vehicle. The explosion was later found to be caused by the failure of two rubber O-rings, responsible for separating sections of the Shuttle's solid rocket boosters. Cold weather the night before the launch caused the O-rings to become brittle. So when the Shuttle launched, hot burning gases from the boosters were able to escape and burn through the exterior of the external tank. The disaster claimed the lives of all seven astronauts aboard the Space Shuttle.

NASA astronaut Scott Kelly, who is currently spending one year on the ISS, said the moment was held "to recognize the sacrifice of all those crew members and how their spirit and legacy lives on in our achievement in space."