About 30 astronauts and cosmonauts have perished in the past 50 years while preparing for or trying perilous space missions. However, the most majority of these fatalities took place either on Earth's surface or in its atmosphere, below the Kármán line, which is considered to be the beginning of space and starts at a height of around 62 miles (100 kilometers). 

However, just three of the approximately 550 people who have traveled into space so far have really perished there.

a dangerous frontier 

Several pilots testing powerful rocket-powered planes perished in a wave of fatal jet crashes that hit NASA and the USSR early in the space race. Then, of course, there was the horrifically fatal fire aboard Apollo 1 in January 1967, which claimed the lives of astronauts Gus Grissom, Ed White, and Roger Chaffee. A stray spark sparked inside the cabin of the grounded spaceship, which was filled with pure oxygen, during a launch simulation. The crew tragically perished as a result of the uncontrollable fire that swiftly overpowered them as they attempted in vain to unlock the pressurized hatch door.

According to Walter Cunningham, Lunar Module Pilot of Apollo 7, "We had done exactly the same test the night before, but without the hatch closed, so we weren't on 100 percent oxygen." So, after the [Apollo 1] crew died, it took a few weeks before they began to put the pieces together, and at that point, we were given the job of leading the first manned Apollo mission. Cunningham, Wally Schirra, and Donn Eisele became the first members of the Apollo crew to successfully enter space less than two years later, in October 1968.