The Tracy brothers from "Thunderbirds" were named after astronauts from which spaceflight programme?

The Tracy brothers were named after Mercury Seven astronauts: Scott Carpenter, John Glenn, Virgil "Gus" Grissom, Gordon Cooper and Alan Shepard. The series' title was derived from a letter written by Gerry's brother, Lionel, while he had been serving overseas as an RAF flight sergeant during World War II. While stationed in Arizona, Lionel had made reference to Thunderbird Field, a nearby United States Army Air Forces base.

"Thunderbirds" is a British science-fiction television series created by Gerry and Sylvia Anderson, filmed by their production company Anderson Provis (AP) Films and distributed by Incorporated Television Company (ITC) Entertainment. It was produced between 1964 and 1966 using a form of electronic marionette puppetry (dubbed "Supermarionation") combined with scale-model special effects sequences. Two series were filmed, comprising a total of thirty-two 50-minute episodes; production ceased following the completion of the second series' sixth episode when Lew Grade, the Andersons' financial backer, failed in his efforts to sell the programme to American network television.