Apollo Soyuz Patch

The Apollo–Soyuz Test Project entailed the docking of an American Apollo spacecraft with the then-Soviet Soyuz spacecraft. Although the Soyuz was given a mission designation number (Soyuz 19) as part of the ongoing Soyuz program, it was referred to simply as "Soyuz" for the duration of the joint mission. The Apollo mission was not officially numbered, though some sources refer to it as "Apollo 18".

The Apollo Command/Service Module (CSM) 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 on the lunar flights, 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 5.0 psi using pure oxygen, while the Soyuz used a nitrogen/oxygen atmosphere at sea level pressure — 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 Soviet Academy of Sciences 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 fitting with the Soyuz 19 was releasable, allowing the two spacecraft to separate.

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 miles of the lunar surface, and was the first general officer to fly into space (he was a brigadier general in the USAF 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 1958, 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 used for this mission during his time as a backup Apollo 15 command module pilot, and had served multiple stints as a backup Skylab commander. The closest he came 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: Alexey Leonov and Valery Kubasov. Leonov became the first man to walk in space on Voskhod 2 in 1965. Kubasov, who flew on Soyuz 6 in 1969, ran some of the earliest space manufacturing experiments. Both were slated 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 to have 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, 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 unmanned as KOSMOS satellites. The third was launched as the manned 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 July 15, and docked on July 17. 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, but a delay resulted in its occurrence being over the town of Metz in France. 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), 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.

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 five days, and the Americans for nine, during which the Apollo crew also conducted experiments in Earth observation.

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 nitrogen tetroxide fumes, caused by the reaction control system (RCS) oxidizer) venting from the spacecraft and reentering a cabin air intake. The RCS was inadvertently left on during descent, and highly toxic nitrogen tetroxide was 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. 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 initiated drogue parachute deployment; these procedures were manually performed later than usual, allowing the ingestion of the propellant fumes through the ventilation system.

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