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Thirty-seven years ago this month, the first joint United States-Soviet Union spaceflight was successfully conducted.  This historic event also marked the first time that spacecraft from two nations successfully rendezvoused and docked in orbit.

The Apollo-Soyuz Test Project (ASTP) was the first international manned spaceflight.  The primary objectives of ASTP were to (1) test the compatibility of rendezvous and docking systems of American and Soviet spacecraft, (2) pave the way for international space rescue and (3) set the stage for future joint manned spaceflights.

The United States flew an Apollo Command-Service Module (CSM) with three men on board; Commander Thomas P. Stafford, Vance D. Brand and Donald K. “Deke” Slayton.  This was Stafford’s 4th time in space while Brand and Slayton were space rookies.  Slayton, one of the original Mercury Seven, had been deprived of a Mercury flight due to what flight surgeons claimed was a heart murmur.  ASTP was Slayton’s ultimate vindication from what he always considered to be a specious medical issue.

The Soviet Union flew a Soyuz spacecraft as part of ASTP.  It was the 19th such vehicle flown by the Soviets.  On board were Cosmonauts Aleksey A. Leonov and Valery N. Kubasov.  ASTP was the second spaceflight for both men.  Leonov held the distinction of being the first human to perform a spacewalk.  That achievement occurred in March of 1965 during the flight of Voskhod 2.

The Apollo CSM carried a special docking module that permitted the spacecraft to dock with the Soyuz.  It also functioned as an airlock since the two vehicles employed different pressurization systems.  Apollo used pure oxygen pressurized to 5.0 while Soyuz utilized a nitrogen-oxygen atmosphere pressurized at 10.0 psia.  Once the Apollo and Soyuz were docked, the docking module also served as conduit between the two spacecraft through which men and cargo could pass.

The ASTP mission began with launch of the Soyuz spacecraft from Baikonur Cosmodrome on Tuesday, 15 July 1975.  Seven and a half hours later, the Apollo spacecraft was launched from LC-39B at Cape Canaveral, Florida.  On Thursday, 17 July 1975, 52 hours after the mission began, the two spacecraft successfull docked in space.  This event marked the first time in spaceflight history that such a feat had been accomplished.

Over the next 48 hours, the crews participated in a variety of activities and exercises.  Crew members from each country were able to transfer to the spacecraft of the other via a tunnel in the docking module.  Ceremonies were held onboard to mark the occasion.  Several dockings and undockings between the two spacecraft were accomplished as well.  A variety of space experiments rounded out the schedule.

On Saturday, 19 July 1975, Apollo and Soyuz undocked for the final time.  The two spacecraft subsequently maneuvered to achieve widely separated orbits.   Following additional time on-orbit in which a variety of space experiments were conducted, each spacecraft returned to Earth.  Soyuz did so on Monday, 21 July 1975.  Apollo followed on Wednesday, 24 July 1975.

ASTP was the last spaceflight conducted by the United States using an Apollo spacecraft.  It also marked the end of America’s initial manned spaceflight effort that began in 1961 with Project Mercury.  ASTP was also the country’s last manned spaceflight of the 1970’s.  Indeed, not until the first flight of the Space Shuttle in April of 1981 that America would once again fly men into space.

Posted in Aerospace, History

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