50 Years Since Sigma 7: “Solved By a Human”

Wally Schirra looks on as artist Cecelia ‘Cece’ Bibby stencils the Sigma 7 logo onto the side of the spacecraft. “Sigma,” wrote Schirra in his autobiography, “a Greek symbol for the sum of the elements of an equation, stands for engineering excellence. That was my goal – engineering excellence. I would not settle for less.” Photo Credit: NASA

On 3 October, NASA will celebrate the passage of five decades since one of most unsung, yet vital, space missions of all time. By the end of 1962, Project Mercury was drawing to a close and President John Kennedy’s goal of human bootprints on the Moon was drawing inexorably closer. Yet only four Americans had ventured into orbit and had spent no more than a handful of hours aloft. To reach the lunar surface would demand a flight of at least a week and a mastery of hundreds of complex systems. On its fifth piloted Mercury mission, the space agency despatched astronaut Wally Schirra for six orbits of the Earth. By the time his spacecraft – Mercury-Atlas-8 (MA-8), better known as ‘Sigma 7’ – hit the waves of the Pacific Ocean, nine hours later, Schirra had spent more time in space than any other American in history and had paved the way for the endurance accomplishments of Project Gemini and, beyond that, Apollo.

Five minutes after launching from Pad 14 at Cape Canaveral, the sustainer engine of Schirra’s Atlas booster shut down and Sigma 7 cleanly separated. “I have SECO,” the astronaut exclaimed as Sustainer Engine Cutoff occurred. He then continued, “Cap sep and in aux damp and it’s very pleasant. Going to fly-by-wire.” By now at an altitude of some 160 miles – higher than any other Mercury astronaut – Schirra set to work evaluating his spacecraft’s systems. “With my eyes fixed on the control panel, studiously ignoring the view,” he wrote in his autobiography, Schirra’s Space, “I began a slow – four degrees per second – cartwheel. Once in the correct orbital position, I checked my fuel. I had used less than half a pound of hydrogen peroxide. The thruster jets worked perfectly. They responded crisply to my touch and shut off without any residual motion. I was able to make tiny, single-pulse spurts, the micromouse farts, to assume an exact position.”

During this time, Schirra oriented his capsule to get a better view of the sustainer as it tumbled away. He concluded that his efforts demonstrated that rendezvous in space (a crucial requirement for reaching and landing on the Moon) was possible in a practical sense. The manual system, on the other, seemed somewhat “sloppy”, with a tendency to ‘overshoot’, and Schirra switched next to the third control mode: the autopilot, which he disparagingly called “chimp mode”. At around this time, his pressure suit began overheating. The suit had been one of Schirra’s areas of responsibility during training and he would comment later on the seriousness of the situation; in fact, Flight Director Chris Kraft even considered terminating the mission after just one orbit. Before launch, Schirra had developed his own technique should overheating occur: he would inject cool water very slowly into the system, advance the temperature knob by half a mark at a time, then wait for ten minutes. He did not want to rush the water, lest the heat exchanger freeze.

It worked. By the end of his first orbit, the temperature had dropped to 32 degrees Celsius, which Schirra considered “hot, but not unbearable”. Flight surgeon Chuck Berry advised Kraft to press on with a second orbit and the news was relayed to Schirra by Capcom Scott Carpenter, based in Guaymas in Mexico.

Pictured aboard Sigma 7 during his nine-hour mission, Wally Schirra went on to command the first fully-fledged orbital rendezvous mission on Gemini VI and led the first Apollo mission into Earth orbit. In doing so, this colourful character became the only man to fly Mercury, Gemini and Apollo missions. Photo Credit: NASA

Schirra was pleased, not only with the prospect of a full-length mission, but with the realisation that the problem was “solved through no great amount of ingenuity, but the point was it was solved by a human”. The need to fly people into space had been vindicated. After the mission, Schirra would receive a plaque, signed by Frank Samonski of Sigma 7’s environmental control system team and emblazoned with the legend that they had ‘sweated more than you did during the first orbit of MA-8’. Affixed to the plaque was the valve used by Schirra to control the water flow to his suit…

Later, as Sigma 7 began its third orbit, Schirra entered a period of drifting flight, during which time he undertook a psychomotor experiment: closing his eyes and touching certain dials on the control panel. “I missed only three out of nine,” he wrote later, “concluding that my sense of direction and distance had not been impaired by weightlessness.” Repowering his ship, high above the Indian Ocean, Schirra switched back to fly-by-wire and successfully fixed his attitude using the Moon in the window as a reference point. Aware that flight controllers had been closely monitoring his fuel consumption, he expressed a hearty “Hallelujah!” when Capcom Gus Grissom, situated at the Kauai station in Hawaii, radioed approval to fly a full six orbits.

On the fifth orbit, busily working through his pre-retrofire checks, Schirra was infuriated to hear a voice interrupt from Quito in Ecuador. “We had what we called a ‘mini-track’ there,” he wrote, “a miniature tracking station, and it wasn’t supposed to come on the air except in an emergency.” The speaker asked the astronaut if he had any words for the people of South America. Schirra, irritated, wished them “Buenos dias, you all”. After splashdown, he would receive a handful of telegrams, complaining of his brusqueness. “But there was one,” he wrote, “I treasured from a US diplomat in Ecuador. He said in effect that Schirra had proved his devotion to the people of Latin America by wishing them a good day.”

Sigma 7 descends beneath its parachute, as Wally Schirra’s “sweet little bird” carries him safely back to Earth. Photo Credit: NASA

Scientific experiments on the mission, thankfully, had been trimmed down, lessons having been learned from the grossly overloaded work schedule on Scott Carpenter’s Aurora 7 flight in May 1962. More time was granted to Schirra to complete each of his tasks. One of the earliest, a little under an hour after launch, was an attempt to observe the million-candlepower flares at Woomera in Australia. Initially, Schirra thought that he had seen them – only to discover that he had actually witnessed enormous lightning flashes – and, when notified that the flare firings were imminent, was hampered by heavy cloud cover. A similar test over Durban in South Africa was ruined by rain showers. The astronaut also had the opportunity to examine the fireflies observed by Carpenter and John Glenn, reporting them to be far too small to photograph and moving, in clouds, at a slower velocity than Sigma 7 itself.

Preparations for re-entry commenced over Africa, when Schirra transitioned to fly-by-wire control to orient Sigma 7 using celestial reference points, then switched to the autopilot to ensure that it operated satisfactorily in this mode. “The flight plan called for me to position the spacecraft using manual controls,” he wrote in his autobiography, “then switch to automatic for retrofire, because the power of the big thrusters offsets the unbalancing force of the retrorockets. The retrorockets exert their force through the centre of the spacecraft, so they don’t kick it off course.” Manual control during retrofire and throughout re-entry had always remained a reserve option for the astronauts. Indeed, on Gordo Cooper’s mission in May 1963, he would experience a failure of his electronics system, forcing him to initiate and guide retrofire entirely by hand.

Wally Schirra is extracted from the Sigma 7 capsule on the desk of the destroyer USS Kearsarge, after completing his nine-hour, six-orbit flight. Schirra’s mission was the longest space voyage ever undertaken by an American astronaut at that time. Photo Credit: NASA

In Schirra’s case, however, the retrorockets of his “sweet little bird” fired perfectly and in sequence under automatic conditions at 4:07 pm EST. Shortly thereafter, he switched the capsule to fly-by-wire, although Sigma 7 was “steady as a rock”, with so much fuel remaining in its automatic and manual supplies that he had to ‘dump’ it during re-entry. Minor adjustments were needed to damp out wobbles after the jettisoning of the retrorocket package, but the descent was as ‘textbook’ as the mission itself. Schirra manually deployed the drogue and main chutes, his elation evident in his words to Capcom Gus Grissom, and splashed down just four miles from the USS Kearsarge at 4:28:22 pm. Within minutes, wrote Schirra, “a whaleboat was alongside and the underwater team had the flotation collar in place”. Stepping aboard the Kearsarge, he noted that it was barely ten hours – and six full orbits – since his launch from Cape Canaveral.

Another surprise awaited him in the admiral’s quarters: an oversized urine-collection bottle, sent specially by the astronauts’ canny nurse, Dee O’Hara. Almost identical to the one that Schirra and Cooper had mischievously dumped on her desk a few weeks earlier, it concluded the perfect mission with the perfect Gotcha.


This is part of a series of History articles which will appear each weekend, barring any major news stories. Next week’s article will focus on STS-26, the mission which saw the Shuttle rise from its knees after the trauma of Challenger.   

Missions » Apollo »


  1. Great article, just one error. The flight of Sigma 7 ended in the Pacific Ocean not the Atlantic, as was correctly mentioned in the earlier article “50 Years Since Sigma 7: A Tale of Turtles”

  2. Question for the author or anyone who can clarify.

    I had heard (perhaps incorrectly) that the “fireflies” were
    actually the effects of some form of radiation on the human
    eye — i.e., they were visible only through particles
    hitting the retina or whatever.

    But in Schirra’s experience (quoting article): “The
    astronaut also had the opportunity to examine the
    fireflies observed by Carpenter and John Glenn, reporting
    them to be far too small to photograph and moving, in
    clouds, at a slower velocity than Sigma 7 itself.”

    This doesn’t seem to square with the “radiation”
    explanation. What *is* the accepted explanation for this?
    Or is it still unkown? Perhaps ball lightning or


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