Apollo–Soyuz

• 1. Introduction

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  Apollo-Soyuz brought together the two most powerful space programs on Earth for the first time in July 1975. On the 17th of July, an American spacecraft and a Soviet capsule drifted toward each other in orbit, their hatches opened, and two commanders reached across the threshold in what became known as the handshake in space. The images broadcast to millions of television viewers that day showed enemies shaking hands above the clouds. How did the most competitive space race in human history end with its two rivals building a door between their ships? What engineering compromises, political calculations, and personal relationships made it possible? And what happened in the moments after the mission that almost ended in tragedy?

• 2. Cold War Context

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  When Nikita Khrushchev delivered his doctrine of peaceful coexistence to the 20th Congress of the Communist Party of the Soviet Union in 1956, it was meant to be a turning point. Yet peaceful coexistence remained mostly theoretical. In 1971, the Soviet press printed a denunciation of American military action in Laos directly alongside a photograph of the Apollo 14 launch, treating the two as morally equivalent images.

  Still, the diplomatic machinery of detente was already grinding forward. After John Glenn's orbital flight in 1962, President John F. Kennedy and Premier Khrushchev exchanged letters that set off a series of talks between NASA Deputy Administrator Hugh Dryden and Soviet scientist Anatoly Blagonravov. Those discussions produced the Dryden-Blagonravov agreement, formalized in October 1962, the same month as the Cuban Missile Crisis. The agreement was formally announced at the United Nations on the 5th of December 1962. It called for sharing data from weather satellites, studying Earth's magnetic field, and jointly tracking the Echo II balloon satellite.

  Kennedy went further, personally interesting Khrushchev in a joint crewed Moon landing. But Kennedy was assassinated in November 1963, and Khrushchev was removed from office in October 1964. With both architects of cooperation gone, the two nations returned to rivalry.

  By April 1971, the USSR had launched Salyut 1, the first piloted orbital space station. The United States had recently sent Apollo 14 to the Moon. Neither side gave the other much coverage. It was the closing of the Vietnam War that finally softened relations enough for a cooperative mission to become conceivable. Soviet leader Leonid Brezhnev framed it in direct terms: the planet, he said, was big enough for peaceful coexistence but too small to be threatened by nuclear war.

• 3. Engineering the Meeting

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  The two spacecraft that would dock in 1975 were built on almost opposite philosophies, and engineers on both sides made their feelings known. Christopher C. Kraft, director of the Johnson Space Center, described the Soviet design this way: NASA relied on redundant components so that crews could switch to backups if instruments failed; each Soyuz component was instead designed for a specific function, and if one failed, the cosmonauts landed as soon as possible. The Apollo spacecraft was designed to be flown by its crew; the Soyuz was designed to be controlled largely from the ground.

  The Soviets returned the criticism. Soviet engineers called the Apollo spacecraft "extremely complex and dangerous." American astronauts developed a low opinion of the Soyuz for exactly the inverse reasons: it gave pilots too little direct control. Glynn Lunney, the Manager of the Apollo-Soyuz Test Program, eventually had to warn the American crew to stop talking to the press. NASA was worried that any perceived slight would cause the Soviets to pull out.

  Meetings in Houston and Moscow between June and December 1971 ground out the compromise. The central engineering problem was that the two spacecraft couldn't simply touch nose to nose. Apollo operated at about 5 psi using pure oxygen. Soyuz used a nitrogen-oxygen atmosphere at sea level pressure, roughly 15 psi. A direct connection would have been dangerous. Engineer Bill Creasy designed the Androgynous Peripheral Attach System, known as APAS, to solve both the pressure problem and the docking geometry. Either spacecraft could be active or passive during the docking maneuver, which was a genuine innovation.

  A purpose-built docking module bridged the two ships, serving simultaneously as an airlock for pressure equalization and as an adapter for the incompatible docking collars. It had to be retrieved from the upper stage of the Saturn IB rocket after launch, exactly as the Apollo Lunar Module had been retrieved on Moon missions. Six ASTP-class Soyuz spacecraft were built in total. Two flew uncrewed as Kosmos satellites for testing. A third flew as the crewed Soyuz 16 rehearsal specifically to test the APAS mechanism. A fourth served as a fueled hot backup at the launch site. By April 1972, both nations had signed an Agreement Concerning Cooperation in the Exploration and Use of Outer Space for Peaceful Purposes, committing to the 1975 launch date.

• 4. The Crews

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  Deke Slayton had been waiting sixteen years for this flight. He was chosen as one of the original Mercury Seven astronauts in April 1959, but an irregular heartbeat grounded him almost immediately. He ran NASA's astronaut office for over a decade, selecting others for flights he couldn't take himself. A lengthy medical program eventually cleared him, and he selected himself for ASTP. At the time of the mission he was the oldest person to fly in space and held the longest gap ever between being selected as an astronaut and actually launching.

  Jack Swigert had originally been assigned as command module pilot for the prime crew but was removed before the official announcement. His punishment was tied to the Apollo 15 postal covers incident, in which astronauts had carried unauthorized postage covers to the Moon. His replacement was Vance Brand, who had trained as a backup on Apollo 15 and served two stints as a backup Skylab commander. His closest prior approach to flying had come as commander of the Skylab Rescue mission, mustered in case the crew of Skylab 3 needed to be retrieved after a fuel leak.

  Thomas Stafford, the mission commander, had already flown three times and had come within eight nautical miles of the lunar surface as commander of Apollo 10. He was a brigadier general in the United States Air Force at the time of the flight. He would retire with three stars in 1979.

  On the Soviet side, Alexei Leonov carried a distinction no one else could claim: he had become the first person to walk in space during the Voskhod 2 mission in March 1965. Valery Kubasov had flown on Soyuz 6 in 1969 and conducted some of the earliest space manufacturing experiments. Both men had been scheduled to fly on Soyuz 11 in 1971, with Leonov as commander and Kubasov as flight engineer, but were pulled from that crew because Kubasov was suspected of having tuberculosis. The crew that flew in their place died when their capsule depressurized during reentry. The two-man configuration of the ASTP Soyuz was itself a consequence of that disaster, as the post-Soyuz 11 design required both cosmonauts to wear Sokol space suits during launch, docking, and reentry.

• 5. Seventeen Days in Space

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  Soyuz 19 and the Apollo spacecraft launched within seven and a half hours of each other on the 15th of July 1975. Two days later, on the 17th of July, they docked. Three hours after docking, Stafford and Leonov exchanged the first international handshake in space through the open hatch of the Soyuz. NASA had calculated the handshake would occur over the British seaside resort of Bognor Regis, but a delay shifted the moment to the skies over Metz, France.

  While the ships were joined, the five crew members worked through a schedule that mixed science with diplomacy in roughly equal measure. They exchanged flags and gifts, including tree seeds later planted in both countries. They signed certificates and visited each other's ships. They ate together and spoke in each other's languages. Stafford's Russian was accented enough that Leonov later joked there were three languages spoken on the mission: Russian, English, and "Oklahomski." They also listened to music from each other's countries; the Soviet contribution included "Tenderness" by Maya Kristalinskaya, while the Americans brought "Why Can't We Be Friends?" by War.

  Scientific work ran alongside the ceremonies. Embryologist Jane Oppenheimer analyzed the effects of weightlessness on fish eggs at various stages of development. After 44 hours together, the ships separated to perform one of the mission's more unusual experiments: the Apollo was maneuvered to create an artificial solar eclipse, allowing the Soyuz crew to photograph the solar corona with their instruments.

  The ships were docked for 1 day, 23 hours, 7 minutes, and 3 seconds in total. After a brief second docking, they went their separate ways. The Soviets remained in orbit for two more days; the Americans stayed for five, conducting Earth observation experiments.

• 6. The Dangerous Descent

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  The mission's most serious crisis arrived not in space but on the way home. During reentry and splashdown of the Apollo, the crew were accidentally exposed to toxic monomethylhydrazine and nitrogen tetroxide fumes. The reaction control system had been left on during descent, and its hypergolic propellants vented from the spacecraft and were pulled back in through a cabin air intake.

  Vance Brand briefly lost consciousness. Stafford retrieved emergency oxygen masks, got one onto Brand, and handed another to Slayton. All three astronauts were hospitalized for two weeks in Honolulu, Hawaii.

  Brand later took responsibility for the error. During reentry, high noise levels in the cabin had made it difficult to hear Stafford read through the checklist, and Brand believed he had missed the call to close two specific switches. Those switches would have automatically shut off the RCS and triggered drogue parachute deployment. When the procedures were finally performed manually, they happened later than planned, and the fumes had already entered through the ventilation system.

  The ASTP was the final flight of any Apollo spacecraft. Immediately after its launch, preparations began to convert Launch Complex 39B and the Vehicle Assembly Building at Kennedy Space Center for the Space Shuttle program. LC-39A had already closed after the Skylab launch. The gap that followed would be the longest the United States had gone without a crewed space mission since the program began; the next American astronauts to fly would launch on STS-1, the first Space Shuttle mission, on the 12th of April 1981.

• 7. A Lasting Blueprint

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  The docking hardware born from Apollo-Soyuz did not retire with the mission. A derivative collar, APAS-89, was launched as part of the Kristall module on the Soviet Mir space station. Originally intended as a docking port for the Buran Soviet space shuttle, it ended up serving the next American-Russian docking mission, STS-71, twenty years later as part of the Shuttle-Mir program. That port was tested first by the last APAS-equipped Soyuz, Soyuz TM-16, in 1993. The American Space Shuttle continued to use APAS-89 hardware for all of its dockings to Mir and later to the International Space Station.

  Today the first Pressurized Mating Adapter, PMA-1, remains the physical interface connecting the Russian-built, NASA-owned Zarya module to the US segment of the ISS. The lineage of the 1975 docking collar is still in use.

  The political legacy was more ambiguous. Each country's press framed the mission to serve its own narrative. Soviet reporting implied the USSR was leading the United States in space; American coverage described the Soyuz as technically primitive. High-profile cooperation declined after 1975 and became entangled in what analysts called linkage politics. But the precedent survived the politics.

  On the personal level, the friendship between Stafford and Leonov proved durable beyond any government program. Leonov became the godfather of Stafford's younger children. When Leonov died in October 2019, Stafford delivered the eulogy. An asteroid discovered in 1977 by Soviet astronomer Nikolai Chernykh carries the mission's name: 2228 Soyuz-Apollo. And at a reunion on the 16th of July 2010, Leonov, Kubasov, Stafford, and Brand gathered at an Omega timepiece store in New York City, thirty-five years after the ships they flew had briefly become one.