On May 21, 1965, NASA released the Gemini 4 press kit. It opened with the standard mission description, in this case for a four-day orbital flight that would send commander Jim McDivitt and pilot Ed White around the Earth 62 times to evaluate “the effects of extended spaceflight on crew performance and physical condition.”

Then there was an intriguing page that hinted at something bigger: “No decision has been made whether in the Gemini 4 mission the crew will engage in extravehicular activity… A decision to undertake the extravehicular test can be made as late as the day before the launch.” The possibility of an EVA on Gemini 4 came as a surprise not only the American people that day, but to many within NASA as well.

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EVAs, colloquially known as spacewalks, were one of the three main program goals for NASA’s Gemini program designed to support the Apollo program. If NASA was going to send men all the way to the moon, there was no point in having them sit inside and look out the window. They were going outside.

The original Gemini program plan called for a tight schedule with launches every eight to ten weeks. Every mission would add something new to NASA’s repertoire with EVAs expected sometime after Gemini 6; Gemini 4 was designed for a week long endurance test using new fuel cells instead of batteries around June of 1965.

But mid-way through 1964 that schedule was starting to slip. The fuel cells weren’t going to be ready for Gemini 4. The US Air Force Agena target vehicle destined for orbital rendezvous practice was also too far from flight ready to be counted on for Gemini 4.

With the mission plan in tatters, Robert Gilruth, the director of the Manned Spaceflight Center, proposed that Gemini 4 be reconfigured into the first EVA flight. It was a bold plan, moving the EVA goal forward by two flights. But if all the hardware could be certified and the crew trained in time, why not?

The new mission was already percolating when White and McDivitt were announced as the crew on July 24, 1964. The astronauts were two among the very select group of people who knew about the EVA goal for their flight. As pilot, White would be the one stepping out.

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By the beginning of 1965, things looked promising. Engineers from McDonnell certified the hatches could open and close in a vacuum; White and McDivitt actually disassembled and assembled a Gemini hatch to make sure they could fix mechanical problems in orbit and come home safely. McDonnell engineers teamed up with the spacecraft’s designer Max Faget to develop the tether that would give White oxygen and a communications link to the spacecraft and a carbon dioxide gun was certified to give him maneuverability.

On March 18, NASA got an unexpected surprise: cosmonaut Alexei Leonov left the safety of his Voskhod spacecraft to perform history’s first EVA. The need for an EVA on Gemini 4 became more pronounced, and the secrecy around the goal increased. Gradually more men were brought on board — one by one administrators came around to the idea of a spacewalk ahead of schedule — but a veil was kept in place to prevent leaks to the press. No one wanted it to look like NASA was rushing into a mission it wasn’t ready for just because the Soviets had managed an EVA first.

In the first week of April, flight director Chris Kraft, one of the few privy to the EVA plan, brought junior flight director Gene Kranz into the fold. He charged Kranz with writing the mission rules and assembling the necessary data packages so controllers in Houston and at tracking sites around the world could support White during the EVA. It was a big job that Kranz dubbed Plan X.

Throughout April and into May, Kranz lived a sort of double life. He planned for comparatively bland long-duration mission by day and by night worked with a special task force of engineers, astronauts, doctors and technicians to figure out how to run mission control during an EVA. The problem for Kranz was that he couldn’t brief the other controllers on EVA procedures before they left for the tracking stations.

So, in the middle of May he called them all into a meeting. He handed each man a double-sealed envelope and gave them strict instructions not to open the envelopes unless he gave them permission. Otherwise they were to be returned, unopened, when the men returned to NASA after the mission. The envelopes were each labeled simply, in one inch letters, “Plan X.” Inside was a document outlining the procedures and all the data the controllers would need during the EVA.

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On May 19, a little over two weeks before launch, every part of the EVA was certified flight ready. All that remained was to tell the country that one of its astronauts was going to walk in space. Some wanted to keep it a secret and tell surprise the media once White was outside while others wanted to announce 24 hours before launch at a press conference. It was associate administrator Robert Seamans who put a stop to the secrecy. It was one thing to work the kinks out of a possible mission in secret, but if all the systems were ready there was no need to hide the facts. He ordered the EVA be included in the press kit.

The same day the press kit was released, Kranz gave controllers the word to open their “Plan X” envelopes. The cover sheet told the men: “The mission rules and plan are to be used with the data you already have; however, these rules cover flight plan activities you have not heretofore considered i.e.; booster rendezvous and extravehicular activity.” One by one they learned what White would be doing during Gemini 4. It was, Kranz said, a hell of a way to find out.

The announcement that Gemini 4 would do an EVA came four days later on May 25. Deputy administrator Hugh Dryden, the last voice calling the EVA a stunt, had finally come around and the mission was given a green light. Finally, the men who had developed the EVA mission under strict secrecy could sit back and watch.

Image: On June 3, 1965, Ed White became the first NASA astronaut to carry out an EVA. Credit: NASA