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Soyuz 7K-TM

Soyuz 7K-TM No. 71 (Kosmos-638)

INSIDER CONTENT

Soyuz 7K-TM No. 72

INSIDER CONTENT

Soyuz-16

Apollo and Soyuz dock in space

In July 1975, the Soviet and American spacecraft, launched from two different continents, conducted a successful rendezvous and docking in space for the first time. During two days of joint operations, the two crews made multiple visits to each-other's vehicles and performed another docking and undocking.

Previous chapter: ASTP launch campaign (INSIDER CONTENT)

Soyuz-19 lifts off

A few minutes before the liftoff of Soyuz Vehicle No. 75 on July 15, 1975, its onboard TV system had failed. Ironically, it was the first Soviet launch covered with live images from Tyuratam starting at 09:58 GMT (12:58 Moscow Time) or more than two hours before the liftoff. (50)

Konstantin Bushuev, Deput Designer General at NPO Energia, called for delaying the launch, but after some discussions, mission management, led by Minister Sergei Afanasiev, decided to proceed with scheduled operations.

A Soyuz-U rocket with the Soyuz-19 spacecraft lifted off from Site 1 in Tyuratam at 12:20 GMT (15:20 Moscow Time, 8:20 a.m. EDT), on July 15, 1975, as it had been planned back in 1972. Commander Aleksei Leonov, the veteran of the legendary Voskhod-2 mission, and Flight Engineer Valery Kubasov, from the Soyuz-6 crew, were onboard.

The four boosters of the first stage were dropped two minutes after liftoff, followed by the jettisoning of the emergency escape unit and the two sections of the payload fairing 160 seconds into the flight. The second (core) stage completed firing and separated at around 300 seconds after liftoff.

Under propulsion of the third stage, the spacecraft successfully entered a 186.35 by 220.35-kilometer orbit with an inclination of 51.8 degrees toward the Equator around 530 seconds after liftoff — all as planned.

Soon after reaching orbit, the problem with TV aboard Soyuz was traced to a switch unit, which could be bypassed. The repair was first tried on a ground prototype of the spacecraft and step-by-step instructions were then relayed to the crew. On July 16, 1975, at 19:35 Moscow Time (16:35 GMT), mission control received color TV images from Soyuz-19.

Around an hour later, at 17:37 GMT, the crew started the 2-hour 34-minute procedure of reducing the atmosperic pressure inside Soyuz-19 from 867 to 539 millimeters of mercury. Later in the evening, the cosmonauts also activated the Biokat-M biological experiment.

Apollo lifts off

As Soyuz-19 was completing its fourth orbit, on the other side of the globe from Tyuratam, NASA astronauts Thomas Stafford, Vance Brand and Donald Slayton took their seats inside the Command Module, CM, of the final Apollo spacecraft to fly. (50)

A Saturn-1B rocket lifted off from Pad 39B of the Kennedy Space Center at Cape Canaveral, Florida, at 19:50:01 GMT (on July 15, 1975). It was 22:50 in Moscow. (If the official numbering of the program had not ended with the final lunar expedition of Apollo-17 in 1972, this launch would be called Apollo-21, counting three launches to the Skylab space station in 1973.)

Around 10 minutes into the flight, the S-IVB second stage of the Saturn-1B rocket with the Apollo spacecraft entered a 155 by 173-kilometer orbit.

The spacecraft then separated from the S-IVB booster, made a 180-degree pitch maneuver and, after some initial struggle with the alignment, Stafford manually piloted the spacecraft to a linkup with the Docking Module, DM, still attached to the front bulkhead of the S-IVB. The spacecraft then separated from the stage along with the DM.

The Apollo then performed two maneuvers, first forming a near-circular 165 by 167-kilometer orbit and then stretching it to a 169 by 233-kilometer ellipse for a planned intercept of Soyuz-19. (50)

In the meantime, the US crew encountered a potentially serious problem when its first attempt to enter the Docking Module was unsuccessful, due to what turned out to be an assembly error. The docking mechanism between the Command and Docking Modules was blocking the transfer tunnel and, subsequently, would prevent joint operations in orbit in case of a successful docking between Apollo and Soyuz. Unlike the Soviet program, there was no back-up US vehicle to perform the mission. Fortunately, after some effort, the crew managed to dismantle the docking mechanism.

Around a day after launch, Soyuz-19 performed a maneuver entering a 222.7 by 225.4-kilometers "assembly" orbit, where it was expected to rendezvous with the Apollo. The cosmonauts also further dropped pressure inside Soyuz to 500 millimeters of mercury.

During the evening of July 16, 1975, the Soyuz-19 crew also established radio contact with the second expedition aboard the Salyut-4 (DOS-4) space station.

Apollo and Soyuz dock in space

After two days in autonomous flight, the Apollo, performing the role of the active vehicle, successfully docked with Soyuz-19, on July 17, 1975, at 16:09:00 GMT (19:12:10 Moscow Time), as the two ships were orbiting the Earth at an altitude of 225 kilometers. For the first time, viewers on Earth saw live images of Soyuz in orbit from the approaching Apollo spacecraft. The docking process was completed successfully within just three minutes.

The ships formed a joint stack with a total mass of 20,977 kilograms and a length of more than 20 meters. There were five people aboard the same orbital assembly for the first time. Simultaneously, two Soviet cosmonauts were working aboard the Salyut-4 space station (DOS-4), so a total of seven people were in space, matching the number reached during the joint Soyuz-6, -7, and -8 mission in 1969, or nearly six years earlier.

The joint stack reached an apogee, the highest point of its orbit of 237 kilometers above the Earth on June 17, 1975, at 17:01:12 GMT.

At 19:13 GMT on July 17, the hatch in the Soyuz Habitation Module leading to the Docking Module of the Apollo was opened and the opposite hatch on the Apollo's DM module was opened four minutes later. In front of live TV cameras, Leonov and Stafford shook hands and exchanged greetings.

Stafford and Slayton then entered the Habitation Module of Soyuz, while Brand remained in the Command Module of the Apollo. The Soviet General Secretary Leonid Brezhnev and the US President Gerald Ford congratulated the crew.

Three more transfers between the two ships took place in the following days, but one Soviet cosmonaut always remained aboard Soyuz and one NASA astronaut inside the Command Module of the Apollo. The emergency procedures called for the crews to remain aboard their partners' vehicles in case of an urgent need for undocking and landing, which would prevent airlock operations for the return back to their respective spacecraft. (50)

Second docking

The Soyuz-19 and Apollo remained docked for nearly two days, until July 19, 1975, at 12:03:20 GMT (15:03 Moscow Time), when the two vehicles undocked. They then spent 30 minutes 19 seconds in formation flying, while Apollo performed an artificial solar eclipse for the crew of Soyuz-19. In the meantime, the crew of Soyuz-19 put the docking mechanism in active position and maneuvered for re-docking with the Apollo, which remained in passive attitude control. The second contact between the ships took place at 12:33:39 GMT on July 19, 1975. As a result, the experiment practically demonstrated for the first time the operation of a docking system where both vehicles could serve as active or passive, depending on the situation, including during a potential rescue mission in space.

During the second docking, Slayton violated some limits for the operation of the docking port, which led to excessive loads on the mechanism, but it withstood them without problems. (52)

This time, the two ships remained in docked position for 3 hours 22 minutes and 52 seconds and undocked for the second and last time at 15:26:12 GMT (18:26 Moscow Time) on July 19, 1975, followed by the Ultraviolet Absorption experiment.

The total time for the ships in docking position reached 46 hours 46 minutes and 44 seconds. During that time, the joint stack covered 1,309,974 kilometers. For a total of 53 hours 09 minutes and 17 seconds, the ships were recorded within 10 kilometers from each other.

Conclusion of the mission

On July 20, 1975, Soyuz-19 performed a solo maneuver, forming a 216 by 219-kilometer landing orbit. The spacecraft then initiated a braking maneuver at 10:10 GMT, sending it into the dense atmosphere. Some 12 minutes later, the Soyuz split into the Decent Module, carrying the crew, the depressurized Habitation Module and the Instrument and Aggregate Module. At an altitude of around 80 kilometers, at 10:28 GMT, a layer of plasma forming around the Descent Module interrupted communications with the crew, but contact was re-established by the time the capsule descended to an altitude of around 30 kilometers. After another 20-kilometer drop, the parachute system was released at 10:37 GMT, followed by a successful touchdown at 10:50 GMT (13:50:51 Moscow Time), 54 kilometers northeast of Arkalyk in Kazakhstan. For the first time in the Soviet space flight, the landing operations were broadcast on TV. (50)

In the meantime, the Apollo remained in orbit until July 24, 1975, to give NASA maximum experience before an anticipated break in the American piloted space flight until at least 1979, even though it would actually last until 1981.

The Command Module reentered over the Indian Ocean and splashed down in the Pacific, 430 kilometers West of Hawaii. It was met by the recovery ship New Orleans. During the parachute descent, vapors of hydrazine from the attitude control thrusters got into the pressurized volume and caused poisoning of the crew, fortunately not lethal. (52) The astronauts donned breathing masks just in time, but still inhaled enough to land them in a hospital after the recovery.

The Apollo spacecraft masses (1109):

Next page: Aftermath of the ASTP project

The article by Anatoly Zak; last update: July 18, 2025

Page editor: Alain Chabot; last edit: July 18, 2025

All rights reserved

Soyuz-19 lifts off from Tyuratam.

Apollo lifts off from Cape Canaveral on July 15, 1975.

Soyuz-19 in orbit as seen from the Apollo. Credit: NASA

Apollo in orbit as seen from Soyuz-19. Credit: NASA

Leonov and Slayton during crew transfer following the Soyuz-19 and Apollo docking. Credit: NASA