On this day (Jan. 27) in 1967, NASA astronauts Virgil “Gus” Grissom, Ed White and Roger Chaffee died in a pad fire inside of the Apollo 1 spacecraft that was supposed to lift off only a month hence. The tragedy shocked NASA, which was then aiming for manned landings on the moon, and caused an in-depth investigation into the spacecraft’s construction and the cause of the fire.
Above, you can see one of the first news reports after the fire took place, from ABC’s Jules Bergman and a correspondent at “Cape Kennedy” (which is called Cape Canaveral today, referring to an area adjacent to the Kennedy Space Center where the launch was supposed to take place.) “It was too late from the beginning,” Bergman said in the report, referring to the frantic effort to get the astronauts out of their burning spacecraft.
An investigation determined that a spark flew from somewhere inside of the spacecraft and easily ignited in the pure-oxygen atmosphere, fuelled by fire-friendly materials inside the spacecraft. The astronauts were unable to get out quickly because the hatch was complicated to open. The redesigned Apollo spacecraft featured a swift-to-open hatch, fewer flammable materials, covered electrical connections (to mitigate against short-circuits), and a mixed atmosphere of oxygen and nitrogen on the ground.
Safety measures arising from the tragedy did help with saving astronauts on other flights, notably Apollo 13. That mission saw an oxygen tank explode en route to the moon in April 1970.
Every year, NASA has a day of remembrance to commemorate lost crews. The Apollo 1 anniversary marks a solemn week in the agency, as it comes one day before the anniversary of the 1986 Challenger explosion that killed seven astronauts (Jan. 28) and a few days before the 2003 anniversary of the Columbia shuttle breakup, which killed another seven people (Feb. 1).
Four cosmonauts have died during spaceflight, all upon re-entry: Vladimir Komarov (during Soyuz 1 on April 24, 1967) and Georgi Dobrovolskiy, Viktor Patsayev, and Vladislav Volkov (during Soyuz 11 on June 30, 1971).
Training accidents have also claimed a few lives; a list of American ones is maintained at the Astronaut Memorial Foundation.