Astronauts Virgil I. "Gus" Grissom, Edward White and Roger Chaffee died during a blaze inside their Apollo capsule while conducting a countdown test on January 27, 1967 three weeks before their scheduled liftoff from Kennedy Space Center.

A cumbersome hatch prevented technicians from rescuing the astronauts as the fire raged inside the Apollo 1 command modules pure oxygen environment. Investigators later determined an electrical short was the fire's most likely cause. An extensive redesign of the Apollo spacecraft, with an emphasis on fireproof materials, was conducted in the wake of the tragedy. The first piloted Apollo mission, Apollo 7, took place in October 1968.

On January 28, 1986, Space Shuttle Challenger exploded shortly after liftoff, killing all seven astronauts aboard. The worst space accident to date, the disaster claimed the lives of Francis R. "Dick:" Scobee, Michael Smith, Judith Resnick, Ellison Onizuka, Ronald McNair, Gregory Jarvis and schoolteacher Christa McAuliffe.

An investigation found that unusually cold weather on launch day weakened O-rings in one of the shuttle's two solid rocket boosters. As a result, hot gases escaped from the booster's casing, causing an explosion in the shuttle's external fuel tank that destroyed the orbiter. Intensive design reviews and safety efforts followed the accident. The shuttle program resumed with the flight of STS 26 in September, 1988.