Wally Schirra was my favorite Mercury astronaut. While Alan Shepard was first to fly and John Glenn the first to orbit, Schirra made a special impression when he flew the penultimate Mercury mission in a six-orbit flight in October 1962. Of the seven original NASA astronauts, Schirra always projected the most upbeat attitude. He loved being a spaceman. Schirra was unique among his Mercury colleagues as being the only one to fly on all three of NASA's first manned vehicles: Mercury, Gemini, and Apollo.
Four of his astronaut colleagues had been assigned to missions before him. Schirra was given the job of summing up Mercury's achievements by piloting an engineering shake-down flight. He was going to double the duration of Glenn's and Carpenter's three-orbit flights and set the stage for Cooper's concluding 22-orbit marathon. He dubbed his Mercury space capsule Sigma 7:
“Since this was to be an engineering evaluation,” he explained, the name chosen for capsule No. 16 was that of an engineering symbol for summation, Sigma, with the number seven added to it for the seven-member Mercury astronaut team. “Thus,” he said, “was derived the name and symbol that was painted on the spacecraft, Sigma 7.” [This New Ocean: A History of Project Mercury, Swenson, Grimwood, & Alexander (1966)]While Schirra's quote from NASA's official history rings a little false in its high-toned diction—and it's funny to hear the summation symbol attributed to engineering rather than to mathematics—the sentiment hits the right note. Schirra was NASA's clean-up man.
Just as the successful flight of Sigma 7 provided a test run of upgraded Mercury systems in preparation for the program's conclusion, Schirra's later Gemini 6 mission was a pioneering experiment in orbital rendezvous. First Schirra saved the entire mission by not automatically hitting the eject button when the first launch attempt scrubbed. A few days later, the launch was successful. Once he and Thomas Stafford piloted their Gemini spacecraft to within a few feet of Borman and Lovell's Gemini 7, NASA knew that the basic plan for orbital rendezvous was feasible for the Apollo moon landing program. NASA also learned to keep a closer eye on its astronaut's personal effects, since Gemini 6 was the first space mission to feature a corned beef sandwich as an in-flight meal, smuggled aboard by a mischievous Schirra (who found something lacking in NASA's paste-based cuisine).
In the Apollo program itself, Schirra commanded the crucial Apollo 7 flight in 1968. More than a year after his Mercury colleague Gus Grissom and crew had died in a fire on the Apollo 1 launch pad, it fell to Schirra to rebuild confidence in the manned spaceflight program. As usual, Schirra delivered, as he and crewmates Eisele and Cunningham flew a textbook mission. The redesigned Apollo capsule passed muster and on its very next flight took Borman, Lovell, and Anders to lunar orbit on Apollo 8.
Apollo 7 was Schirra's last flight, bringing his personal record to nearly 300 hours of flight time. It was by no means a record among his colleagues at the time (Borman and Lovell had clocked a full two weeks in orbit during the Gemini 7 flight alone), but it was a record of distinction. Schirra was there at every key moment of the space program's progress toward the 1969 moon landing, in Mercury, Gemini, and Apollo.
In my peak space-geek years in high school, I assembled several model spacecraft from the Revell catalog of scale miniatures. When it came time to apply the finishing touches to my Mercury capsule, I naturally picked out the decal that bore the Sigma 7 logo. That was how it all added up.