Seven astronauts (the Mercury Seven) were selected to fly during the Mercury program. Yet Slayton, one of the Mercury Seven didn't fly during Mercury (though he did fly for Apollo-Soyuz). Why were there only six crewed Mercury flights? Did one of the Mercury flights get cancelled, or were there only supposed to be six flights and was one extra astronaut selected as backup?

  • $\begingroup$ A seventh crewed Mercury flight was cancelled in order to drive the Gemini program as preparation for the Apollo moon program. I also think Deke got ill or something. Alan Shepard should eventually have flown the capsule he wanted to call Freedom 7 II. $\endgroup$ Jun 28, 2020 at 12:35
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    $\begingroup$ If you were in charge of a squillion-dollar project would you use the minimum components - here, astronauts - or include some spares? $\endgroup$ Jun 28, 2020 at 22:38
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    $\begingroup$ Having 6 astronauts for each flight which only needs one is more than enough spare. $\endgroup$
    – eckes
    Jun 29, 2020 at 8:40
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    $\begingroup$ I've just been reading a biography about Stapp (Sonic Wind, by Ryan). Stapp was helping with the selection process, building on his Manhigh experience, and he gave them TWELVE! He was upset when that was pared down to seven; there were no spares, and the seven knew it and could use that to their advantage. $\endgroup$
    – Greg
    Jun 29, 2020 at 18:17
  • $\begingroup$ @eckes Worst case: After five failed flights you have only one astronaut, but no spare left. $\endgroup$ Jun 30, 2020 at 18:07

1 Answer 1


It wasn’t originally intended for the astronauts to be matched 1-to-1 with the flights; four additional crewed Mercury-Redstone (suborbital) and three more Mercury-Atlas (orbital) flights were planned but canceled. The additional suborbital missions were canceled to put a man in orbit sooner, and the last orbital missions were canceled as NASA shifted focus to the upcoming Project Gemini.

Mercury astronaut Deke Slayton was grounded for a heart condition, so it was actually somewhat coincidental that the program ended up with six flights and six available astronauts. Without the time pressure coming from the USSR’s Vostok program and Kennedy’s lunar challenge, most of the Mercury astronauts would probably have flown twice during the program.

  • $\begingroup$ NASA Astronaut Group 2 was announced between Carpenter's and Schirra's Mercury flights. Had the Mercury program continued, it is plausible that these new astronauts would have also flown. But your assertion of the Mercury 7 flying twice is essentially correct; everyone who wanted to fly again eventually got a second chance. The only exception was Carpenter, who was subject to much criticism of his flight -- mostly undue -- and seemed glad to leave NASA. $\endgroup$
    – DrSheldon
    Jul 1, 2020 at 17:16
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    $\begingroup$ I guess it would depend on how long AG2 were held in training versus how fast the final Mercury-Atlas flights were sequenced. $\endgroup$ Jul 1, 2020 at 17:26

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