The source data comes from CSIS. CSIS notes that the definition of “astronaut” is not unanimously agreed upon among the world’s space launch providers. The CSIS database includes all those who have flown to an altitude of 100 kilometers or higher. This particular definition of “outer space” is used by the World Air Sports Federation (FAl), an international record-keeping body for aeronautics and astronautics. This database also includes those who were killed in a space-bound mission, like the first-time astronauts aboard STS-51-L. It does not include, however, those who have flown to altitudes below 100 kilometers or first-time astronauts who were killed in non-space-bound missions without having previously flown to space.
Edouard Mathieu and Max Roser (2022) – “Space Exploration and Satellites”. Published online at OurWorldInData.org. Retrieved from: https://ourworldindata.org/space-exploration-satellites [Online Resource]