Apollo-Soyuz Test Project (1975): The Handshake in Space

The Apollo-Soyuz Test Project was the first international crewed space mission, flown jointly by the United States and the Soviet Union in July 1975. On 17 July an American Apollo spacecraft docked with the Soviet Soyuz 19 in Earth orbit, and the commanders Thomas Stafford and Alexei Leonov shook hands through an open hatch. Coming after nearly two decades of space race rivalry, the “handshake in space” became the best-known symbol of Cold War detente.

Background: from race to partnership

From the launch of Sputnik 1 in 1957 to the Moon landings of 1969–1972, spaceflight was a field of intense competition between the superpowers. Yet scientists on both sides had discussed cooperation for years, and there was a practical argument for it: if a crew were stranded in orbit, a spacecraft from the other country could not rescue them because their docking systems were incompatible.

In 1970 and 1971 NASA and the Soviet Academy of Sciences held technical talks on compatible docking equipment. The political breakthrough came at the Moscow summit of May 1972, during the period of relaxed tension known as detente. On 24 May 1972 President Richard Nixon and Soviet Premier Alexei Kosygin signed an agreement on cooperation in space, which committed both sides to a joint docking mission in 1975.

Engineering the link-up

The two spacecraft were very different. Apollo’s cabin used pure oxygen at about one-third of sea-level pressure, while Soyuz used a nitrogen-oxygen mixture close to ordinary air. Moving directly between them would have risked decompression sickness, the “bends” familiar to divers.

The solution was a docking module, built in the United States and launched with Apollo. About 3 metres long, it served as an airlock in which crew members could adjust to the other ship’s atmosphere. For the mission the Soviets also lowered the pressure inside Soyuz, shortening the time needed to transfer.

Engineers on both sides designed a new androgynous docking system, in which the two halves were identical, so that either craft could play the active role. Its descendants were later used on Space Shuttle flights to the Russian Mir station and on the International Space Station.

Before the joint flight, the Soviet Union tested its modified spacecraft and docking equipment. Two uncrewed Soyuz craft were flown under the cover name Kosmos in 1974, and in December 1974 the crewed Soyuz 16 spent six days in orbit as a full rehearsal for the mission.

The crews trained in each other’s countries and studied each other’s languages. The Americans spoke Russian and the Soviets English during the mission, so that each was speaking the language the listener understood less well. Leonov later joked that there were three languages on the flight: English, Russian and “Oklahomski”, a reference to Stafford’s accent.

The crews

The Soviet commander, Alexei Leonov, had made the first spacewalk in 1965. His flight engineer, Valeri Kubasov, had flown on Soyuz 6 in 1969 and carried out early experiments in welding in space.

The American commander, Thomas Stafford, was a veteran of two Gemini missions and of Apollo 10, the dress rehearsal for the first Moon landing. Vance Brand was the command module pilot. The docking module pilot, Donald “Deke” Slayton, was one of the original Mercury Seven astronauts chosen in 1959. He had been grounded in 1962 because of an irregular heartbeat and finally reached space at the age of 51.

The mission

Soyuz 19 lifted off from the Baikonur Cosmodrome on 15 July 1975. About seven and a half hours later, Apollo was launched on a Saturn IB rocket from the Kennedy Space Center in Florida. Over the next two days Apollo chased Soyuz, which acted as the passive target.

The two spacecraft docked on 17 July 1975, about 52 hours after the Soyuz launch. About three hours later, after the pressure had been equalised, the hatch was opened and Stafford and Leonov shook hands. The mission was unusually open for the Soviet programme: the launch of Soyuz 19 was shown live on television, and Western journalists followed the flight closely. Soviet leader Leonid Brezhnev sent a message of congratulation, and President Gerald Ford spoke to the crews by radio.

The ships stayed docked for about 44 hours. The crews exchanged visits, shared meals, swapped flags and gifts, and carried out joint experiments. In one, Apollo moved away and blocked the Sun so that the Soyuz crew could photograph the solar corona in an artificial eclipse.

The spacecraft separated on 19 July, briefly redocked to test the system with Soyuz in the active role, and then parted for good. Soyuz 19 landed in Kazakhstan on 21 July. Apollo stayed in orbit for three more days for American experiments.

A dangerous descent

As Apollo descended on 24 July, two switches were not thrown in time and the control thrusters kept firing. Toxic nitrogen tetroxide fumes were drawn into the cabin through a pressure-relief valve. Stafford managed to put on oxygen masks for the crew, but all three men had inhaled the gas.

After splashing down in the Pacific Ocean west of Hawaii, the astronauts were taken to hospital in Honolulu, where they were treated for chemical pneumonia and kept under observation for about two weeks. All three recovered fully.

By the numbers

Timeline

• 1972, 24 May: Nixon and Kosygin sign the space cooperation agreement in Moscow.
• 1975, 15 July: Soyuz 19 launches from Baikonur; Apollo follows from Florida about seven and a half hours later.
• 1975, 17 July: The spacecraft dock in orbit and Stafford and Leonov shake hands.
• 1975, 19 July: The ships undock, redock briefly for a test and separate.
• 1975, 21 July: Soyuz 19 lands in Kazakhstan.
• 1975, 24 July: Apollo splashes down in the Pacific; the crew are hospitalised after inhaling toxic fumes.
• 1975, 1 August: The Helsinki Final Act is signed, another high point of detente.

Legacy

Apollo-Soyuz was the last flight of an Apollo spacecraft. American astronauts did not return to space until the first Space Shuttle mission in 1981. Detente itself faded in the late 1970s, especially after the Soviet invasion of Afghanistan in 1979, and joint crewed flights did not resume for almost twenty years. At the time, some American critics argued that the project gave the Soviet Union access to Western technology and prestige without equal benefit to the United States, while supporters saw it as a low-cost investment in trust.

The mission’s influence nonetheless proved lasting. It established working relationships, technical standards and habits of cooperation that were revived in the 1990s, when Space Shuttles docked with the Mir station and the two countries became partners in the International Space Station. Leonov and Stafford remained close friends for the rest of their lives.

Why it matters

Coming just weeks before the Helsinki Accords, the handshake in orbit showed that the Cold War rivals could work together on one of the most demanding technical tasks of the age. It turned spaceflight from a race into a partnership and laid the foundations for later international space stations.