Apollo–Soyuz

It was American astronaut Deke Slayton's only space flight. He was chosen as one of the original Mercury Seven astronauts in April 1959, but had been grounded until 1972 for medical reasons.[9]

Jack Swigert had originally been assigned as the command module pilot for the ASTP prime crew, but he was removed before the official announcement as punishment for his involvement in the Apollo 15 postal covers incident.[10]

Support crew

Karol J. Bobko, Robert Crippen, Robert F. Overmyer, Richard H. Truly

Flight directors

Pete Frank (Orange team), Neil Hutchinson (Silver team), Don Puddy (Crimson team), Frank Littleton (Amber team)

A Saturn IB launch vehicle lifts the American ASTP crew into orbit.

Soyuz as seen from Apollo CM

The ASTP entailed the docking of an American Apollo command and service module (CSM) with a Soviet Soyuz 7K-TM spacecraft. Although the Soyuz was given a mission designation number (Soyuz 19) as part of the ongoing Soyuz programme, its radio call sign was simply "Soyuz" for the duration of the joint mission. The Apollo mission was not a numbered mission of the Apollo program, and similarly bore the call sign "Apollo". Despite this, the press and NASA have referred to the mission as "Apollo 18", but this should not be confused with the canceled lunar mission.[11][12][13][14][15]

The Apollo spacecraft was launched with a docking module specially designed to enable the two spacecraft to dock with each other, used only once for this mission. The Saturn IB launch vehicle and CSM were surplus material. Like the Apollo Lunar Module, the docking module had to be retrieved from the S-IVB upper-stage of the Saturn IB rocket after launch. The docking module was designed as both an airlock — as the Apollo was pressurized at about 5 psi (34 kPa) using pure oxygen, while the Soyuz used a nitrogen/oxygen atmosphere at sea level pressure (about 15 psi (100 kPa)) — and an adapter, since the surplus Apollo hardware used for the ASTP mission was not equipped with the APAS docking collar jointly developed by NASA and the Academy of Sciences of the Soviet Union for the mission. One end of the docking module was attached to the Apollo using the same "probe-and-drogue" docking mechanism used on the Lunar Module and the Skylab space station, while its other end had the APAS docking collar, which Soyuz 19 carried in place of the standard Soyuz/Salyut system of the time. The APAS collar fitted onto Soyuz 19 was releasable, allowing the two spacecraft to separate in case of malfunction.

The Apollo flew with a three-man crew on board: Tom Stafford, Vance Brand, and Deke Slayton. Stafford had already flown into space three times, including within eight nautical miles of the lunar surface as Commander of Apollo 10, and was the first general officer to fly into space. 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. Slayton was one of the original Mercury Seven astronauts selected in 1959, but an irregular heartbeat grounded him until 1972. He became head of NASA's astronaut office and, after a lengthy medical program, selected himself for this mission. At the time, Slayton was the oldest person to fly in space and the one with the longest gap between selection as an astronaut and first flight into space. Brand, meanwhile, had trained with the Apollo spacecraft during his time as a backup Apollo 15 command module pilot, and had served two stints as a backup Skylab commander. The closest he had come to flying prior to ASTP was as commander for the Skylab Rescue mission mustered to potentially retrieve the crew of Skylab 3 due to a fuel leak on that mission's Apollo CSM.

The Soyuz flew with two men: Alexei Leonov and Valeri Kubasov. Leonov became the first man to walk in space on Voskhod 2 in March 1965. Kubasov, who flew on Soyuz 6 in 1969, ran some of the earliest space manufacturing experiments. Both were to have flown on the ill-fated Soyuz 11 in 1971 (Leonov as commander, Kubasov as the flight engineer), but were grounded because Kubasov was suspected of having tuberculosis. The two-man crew on the Soyuz was a result of the modifications needed to allow the cosmonauts to wear the Sokol space suit during launch, docking, and reentry.

The ASTP-class Soyuz 7K-TM spacecraft used was a variation of the post-Soyuz 11 two-man design, with the batteries replaced by solar panels enabling "solo" flights (missions not docking to one of the Salyut space stations). It was designed to operate, during the docking phase, at a reduced nitrogen/oxygen pressure of 10.2 psi (70 kPa), allowing easier transfers between the Apollo and Soyuz. Six ASTP-class Soyuz spacecraft were built in total, including the one used. Before the actual mission, two craft were launched uncrewed as Kosmos satellites. The third was launched as the crewed Soyuz 16 flight as a rehearsal in order to test the APAS docking mechanism. Another craft was used fully fueled as a "hot backup" at the launch site – later it was disassembled. And the sixth craft was available as a "cold" backup; it was later used on the last "solo" Soyuz flight in 1976, but with the APAS docking adapter replaced by the MKF-6 multispectral camera.

The Soyuz and Apollo flights launched within seven-and-a-half hours of each other on 15 July 1975, and docked on 17 July 1975. Three hours later, the two mission commanders, Stafford and Leonov, exchanged the first international handshake in space through the open hatch of the Soyuz. NASA had calculated that the historic handshake would have taken place over the British seaside resort of Bognor Regis,[16] but a delay resulted in its occurrence being over the city of Metz in France.[17] During the first crew exchange, the crews were read a statement from Soviet Premier Leonid Brezhnev, and received a phone call from U.S. President Gerald Ford.

While the two ships were docked, the three Americans and two Soviets conducted joint scientific experiments, exchanged flags and gifts (including tree seeds which were later planted in the two countries), listened to each other's music (examples include "Tenderness" by Maya Kristalinskaya[18] and "Why Can't We Be Friends?" by War[19]), signed certificates, visited each other's ships, ate together, and conversed in each other's languages. (Because of Stafford's pronounced drawl when speaking Russian, Leonov later joked that there were three languages spoken on the mission: Russian, English, and "Oklahomski".) There were also docking and redocking maneuvers, during which the two spacecraft reversed roles and the Soyuz became the "active" ship.

American scientists developed four of the experiments performed during the mission. Embryologist Jane Oppenheimer analyzed the effects of weightlessness on fish eggs at various stages of development.[20]

After 44 hours together, the two ships separated, and maneuvered to use the Apollo to create an artificial solar eclipse to allow the crew of the Soyuz to take photographs of the solar corona. Another brief docking was made before the ships went their separate ways. The Soviets remained in space for two more days, and the Americans for five, during which the Apollo crew also conducted Earth observation experiments.

• 
  Soyuz 19 as seen from the Apollo
• 
  Mission control center in Houston during ASTP
• 
  The historic handshake between Stafford and Leonov
• 
  U.S. President Gerald Ford speaks to the Soviet and American crews on 18 July 1975.
• 
  Deke Slayton (right) with Leonov in the Soyuz spacecraft
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  The astronauts and cosmonauts assembled this commemorative plaque in orbit as a symbol of the international cooperation.

The mission was considered a great success, both technically and as a public-relations exercise for both nations. The only serious problem was during reentry and splashdown of the Apollo craft, during which the crew were accidentally exposed to toxic hydrazine and nitrogen tetroxide fumes, caused by unignited reaction control system (RCS) hypergolic propellants venting from the spacecraft and reentering a cabin air intake. The RCS was inadvertently left on during descent, and the toxic fumes were sucked into the spacecraft as it drew in outside air. Brand briefly lost consciousness, while Stafford retrieved emergency oxygen masks, put one on Brand, and gave one to Slayton. The three astronauts were hospitalized for two weeks in Honolulu, Hawaii.[21] Brand took responsibility for the mishap; because of high noise levels in the cabin during reentry, he believes he was unable to hear Stafford call off one item of the reentry checklist, the closure of two switches which would have automatically shut off the RCS and begun drogue parachute deployment. These procedures were manually performed later than usual, allowing the ingestion of the propellant fumes through the ventilation system.[22]

The ASTP was the final flight of an Apollo spacecraft. Immediately after the launch of the Apollo spacecraft, preparations began to convert LC-39B and the Vehicle Assembly Building at Kennedy Space Center for use by the Space Shuttle, the United States' next crewed spacecraft program. LC-39A had already been closed after the launch of Skylab.

Apollo–Soyuz painting

A derivative (but mechanically incompatible) docking collar, APAS-89, was launched as part of the Kristall module of the Soviet Mir space station. Originally intended as the docking port for the (defunct) Buran Soviet space shuttle, the APAS-89 unit was used for the next Russian-American docking mission, STS-71, twenty years later as part of the Shuttle–Mir program (though not before the docking port was tested by the last APAS-equipped Soyuz, Soyuz TM-16, in 1993).

The American Space Shuttle continued to use the same APAS-89 docking hardware through the end of the Space Shuttle program to dock to Mir and then the International Space Station, the latter through the Pressurized Mating Adapters (PMAs).

The PMAs are equipped with the later APAS-95 adapters, which differ from the APAS-89 adapters in that they are no longer androgynous; while compatible with the APAS-89 docking collars, they are not capable of acting as the "active" partner in docking.

The first PMA, PMA-1, remains in use as the interface connecting the Russian-built, NASA-owned Zarya module to the US segment of the ISS (USOS), and so the APAS continues in use to this day (2021).

Apollo–Soyuz was the first joint US–Soviet space mission. At the time it was thought that space would become either more international or competitive as a result, but it became both. The mission became symbolic of each country's goals of scientific cooperation, while their news reports downplayed the technical prowess of the other. Soviet press implied that it was leading the United States in space flight, tying it to Marxist ideology, while the United States reported that the Soyuz was technically primitive.[23] High-profile space cooperation declined after the successful mission and became entangled in linkage politics, but it set a precedent of cooperation that continued in the Shuttle–Mir Program.[24][25]

The American and Soviet commanders, Stafford and Leonov, became lasting friends. Leonov was the godfather of Stafford's younger children.[24][26] Stafford gave a eulogy at Leonov's funeral in October 2019.[27]

An asteroid, 2228 Soyuz-Apollo, discovered in 1977 by Soviet astronomer Nikolai Chernykh, is named after the mission.[28]

A large Soyuz–Apollo monument was constructed outside TsUP (the Soviet, later Russian space control center) in Moscow. It consisted of a metal scale model of Earth overarched by an arc terminating in the joined Soyuz–Apollo spacecraft. It was damaged when a vehicle collided with it in the late 1990s, and was removed for repairs.

The mission control room that hosted the Americans in Korolyov, Russia, was preserved as a memorial to the Soyuz–Apollo mission.[26]