Полет кораблей "Союз" и "Аполлон"  (автор картины Robert McCall)
Soyuz and Apollo in flight
(painting by Robert McCall)
The program of the joint experimental mission of the US and Soviet spacecraft of Apollo and Soyuz types (abbreviated to ASTP - Apollo-Soyuz Test Project), was approved by the Agreement between USSR and USA on the cooperation in the research and use of space for peaceful purposes dated 24, 1972.


Appointed as the directors of the project were: On the Soviet side – corresponding member of the USSR Academy of Sciences K.D.Bushuev, on the US side – doctor G. Lunney.

В.Н. Кубасов, А.А. Леонов, К.Д. Бушуев, Г.С. Ланни, Т. Стаффорд, В. Бранд, Д. Слейтон. Космический центр им. Джонсона (США). Апрель 1974 г.
V.N.Kubasov, A.A.Leonov,K.D.Bushuev, G.S.Lunney, T.Stafford, V.Brand, D.Slayton.
Johnson Space Center (USA). April 1974.

Historical background

Contacts between Soviet and US scientists began as early as the launches of the first Soviet artificial Earth satellites. The first agreement on cooperation in peaceful space exploration between the Academy of Sciences of the USSR and NASA was signed in June 1962. It was then that a broad exchange of opinions and mutual reviews of results of space experiments began.
Discussions of possible cooperation between USSR and USA in the field of manned spaceflight were initiated by the president of the USSR Academy of Sciences academician M.V.Keldysh and director of the National Aeronautics and Space Administration (NASA) Dr. Paine.
In October 1970 the first meeting of specialists from USSR and USA was held. The delegations were headed by: US delegation – director of the Johnson Manned Spacecraft Center R.Gilruth, Soviet delegation – chairman of the Council for International Cooperation in Space Exploration and Use ("Intercosmos") under the aegis of the USSR Academy of Sciences academician B.N. Petrov. Working groups were set up to coordinate engineering requirements for compatibility between Soviet and US spacecraft.
In 1971, first in June in Houston, and then in November in Moscow, meetings were held between specialists from the USSR Academy of Sciences and US NASA. These meetings reviewed engineering requirements for spacecraft systems, agreed on critical engineering solutions and ground rules for assuring systems compatibility, as well as the feasibility of carrying out in mid-1970s manned missions using existing spacecraft.

Пленарная встреча советских и американских специалистов по программе «Союз–Аполлон». Июль 1972 года. Хьюстон
Plenary session of Soviet and US specialists under Soyuz-Apollo program.
July 1972. Houston

Main objectives of ASTP

The main objectives of the program were:

  • to develop and test elements of a compatible orbital rendezvous system;
  • to develop and test androgynous (active/passive) docking assemblies;
  • to test hardware and equipment for mutual crew transfers from one spacecraft to the other;
  • to gain experience in joint missions of spacecraft from USSR and USA, including, if need be, rescue in emergency situations;
  • to study the feasibility of controlling the attitude of the docked spacecraft, of vehicle-to-vehicle communications;
  • Coordination of activities between US and Soviet mission control centers.

Preparation for the mission

In the course of preparations for the mission, Soviet and US designers solved many difficult problems of compatibility between equipment for mutual search and approach of spacecraft, their docking assemblies, life support systems, communications and mission control equipment, etc.
At NASA request, the mission date was established in 1973. The final flight readiness document was signed on May 24, 1975, for USSR by academician V.A.Kotelnikov, for US by Dr. G. Low. The vehicles launch date was approved.

How the spacecraft were prepared

Preparations for the joint mission involved solving a lot of difficult problems. One of them was different gas atmosphere in the spacecraft cabins. Atmospheric control and supply systems on spacecraft from different countries were significantly different. In Soyuz spacecraft air composition and pressure are close to their normal values on Earth. US astronauts breathed almost pure oxygen at low pressure. Pure oxygen allowed saving mass, since oxygen plant weighs less, but it significantly increased the fire hazard. One spark would suffice to set the spacecraft ablaze.
In addition to this, transfer from one spacecraft to the other could result in bodily injuries cased by the sudden change in the atmosphere. To address this problem, a special transfer compartment-airlock was developed and launched together with the Apollo spacecraft. The design of the transfer compartment used some lunar module heritage, in particular, it had the same docking unit for connecting with the spacecraft. The atmospheric pressure in the Apollo capsule was somewhat raised, while in Soyuz it was lowered down to 530 mm Hg, while oxygen content was increased up to 40%. As a result of these measures, the duration of the debreathing (eliminating nitrogen from the body by breathing oxygen in order to prevent decompression sickness) during airlocking was reduced from 8 hours to 30 minutes.
The specialists also had to face other problems, no less complicated. Five working groups of specialists from both sides started looking for ways to bring the engineering capabilities of the spacecraft closer together.
V.P.Legostaev on the Soviet side, D. Cheatham and H.Smith on the US side headed the team which was to achieve compatibility between the spacecraft rendezvous systems. These systems turned out to be completely incompatible. Although both spacecraft used radio systems to measure range during rendezvous, their operating frequencies and methods of obtaining information were different. Moreover, on Soyuz spacecraft the relative range is measured using a radio system, while on Apollo, along with radio systems, optical equipment is also used. The specialists in this team had to work very hard to find the right solution.
Arguably the most challenging work fell to the team of specialists headed by V.S.Syromyatnikov, D.Wade and R.White. As it happens, the docking assemblies on Soyuz and Apollo, while based on the same general concept of probe and drogue, were nevertheless incapable of working together. The had no choice but to develop a new common design, which would be able to support docking with any spacecraft, regardless of whether it is active or passive. It was thus that a radically new type of design was born – the androgynous peripheral docking assembly.

На рисунке А.А. Леонов изобразил два стыковочных узла: синий - американский, красный - корабля "Союз"
Стыковочный узел 

In the picture A.A. Leonov drew two docking units: The blue one belongs to the US spacecraft, the red one to Soyuz.
There was one more snag: Soyuz and Apollo have different mass. How are they going to behave in space during docking?
In a word, difficulties were aplenty. An orbit was found which was the most suitable for integrating Apollo and Soyuz into single house in space, a transfer compartment/docking module was designed, which was 3.2 long, with a diameter of bit less than two meters (shown in the figure to the left).
Integration of engineering solutions into the project, trajectory support, scientific experiments and many other things related to the project as a whole fell to the team of specialists headed by V. A. Timchenko and P. Frank.
There was also such a problem as organizational compatibility. This included efforts to find a match between the structures of different specialist organizations and clarify terminology and conventional designations, to select common coordinate systems, inputs for joint calculations, formats and contents of documents to support communication and exchange of data, to agree upon procedures for specific operations, issues involved in training cosmonauts and ground personnel.
Many of those things were done for the first time, many of the solutions could only be verified in actual practice. Tests of the modified version of Soyuz included 3 flights – two unmanned flights and one manned flight of Soyuz-16. The manned flight took place in December 1974 – seven months before the launch of Soyuz-19 and Apollo (for details about that flight see the article "40th anniversary of Soyuz-16 mission" on our web site).

Training of the crews

Состав экипажей

The list of the crew

Soviet crewmembers:

  • Alexei Leonov – commander, his 2nd mission
  • Valery Kubasov – flight engineer, his 2nd mission.

US crewmembers:

  • Thomas Stafford – commander, his 4th mission
  • Vance Brand – command module pilot, his 1st mission
  • Donald Slayton – docking module pilot, his 1st mission.

The first time the complete complement of the joint crew met was on November 19, 1973 in Star City
A major problem in the crew training was studying the language of the other country. Two years were set aside for the training, and during that time the five crewmembers got to perfectly understand each other using what was jokingly referred to as "Ruston", a mix of English and Russian. Ruston (the word derives from the merger of "Russian" and "Houston") caused a lot of trouble to the technical personnel of the ASTP program on both Soviet and US sides. Sometimes even very experienced translators were unable to translate conversations during joint training sessions. Eventually, it was proposed that during the mission the Americans should speak Russian, and the Russians should speak English.
As for the technology, everything was much simpler. Both Russians and Americans jointly worked in the simulators getting to know each other's technology. Soviet cosmonauts got to know Apollo and the US astronauts got to know Soyuz so well that they could replace each other and work in mixed crews.

К.Д. Бушуев (в центре) рассказывает экипажам об особенностях корабля "Союз"
K.D.Bushuev (in the center) tells the crews about the features of the Soyuz spacecraft

«Insurance" against a contingency

In case Soyuz-19 had to wait for Apollo in orbit too long, or had for some unforeseen reason to make an early landing, its place in orbit would have been taken by Anatoli Filipchenko and Nikolai Rukavishnikov who were to be launched on a backup Soyuz for a second attempt to meet with Apollo. Those were experienced cosmonauts, who had already flown on Soyuz-16 and conducted tests on the spacecraft modified for docking and operations with Apollo.
The Earth has also developed a detailed plan of actions against the possibility of something going wrong with Soyuz and Apollo rendezvous. For example, if Apollo had not been able to lift off due to bad weather, the Soyuz would have waited for it in orbit for an extra day or two, or three or even four. Agreed and included into onboard documentation were the actions in case a docking device or orientation lights fail on one of the spacecraft. There were also provisions for crew actions in case spacecraft lost its pressure integrity, radio equipment failed, fire started, etc..

Mission Control Centers

The Soviet Mission Control Center supported the implementation of the Apollo-Soyuz project together with the US MCC. A challenging task fell to the specialists headed by A.S. Yeliseev and P.Frank: to control spacecraft missions from two locations separated by a long distance is a difficult task by itself. And here they had to coordinated the work of Soviet and US specialists, who had many years of traditions and experience, which were not always the same.
Starting on June 27, 1975, direct phone and TV links were established between Moscow and Houston.
On June 29, 30 and July 1 an integrated joint training session was held. The Soviet crew sat in the Soyuz simulator in the Star City, and the US crew in Apollo simulator in Houston. The entire personnel of the Soviet and US Mission Control Centers were also sitting at their workstations. The duration of this session was exactly the same as the time the crews were supposed to spend in space from the moment of the spacecraft rendezvous till their undocking and conducting two joint scientific experiments. Examiners asked the crew tricky questions, ran off-nominal situations.
The training session ended successfully. The crews earned excellent grades. Their readiness for the mission was confirmed.

Mission timeline

On July 15, 1975 at 15 h 20 min (Moscow Time) Soyuz-19 carrying cosmonauts A.A. Leonov and V.N. Kubasov was launch from the Baikonur Cosmodrome, and at 22 h. 50 min the Apollo carrying astronauts T. Stafford, D.Slayton and V.Brand was launched from the launch site at Cape Canaveral (Florida).

А.А. Леонов и В.Н. Кубасов перед стартом
A.A.Leonov and V.N.Kubasov before launch

Soyuz-19 went into an orbit that was very close to its desired orbit. The first few orbits of the spacecraft are not circular, but elliptical with the perigee distance of 186 km and apogee distance of 221 km. The Apollo was launched into the Soyuz orbital plane, and at the moment when it entered space the spacecraft were separated by about six thousand kilometers.
During the fourth orbit the first maneuver to form the Soyuz orbit was performed. A repeated orbital correction was performed during the seventeenth orbit in order to finalize the assembly orbit. At that time the spacecraft was moving in a circular orbit at the distance of 225 kilometers from Earth. The Apollo crew also performed their first maneuver so as not to lose sight of Soyuz..
By 12 hours Moscow Time on July 17, 1975, the Soyuz had completed 30 orbits, out of which 13 orbits were in the assembly orbit. The positional error was just 250 meters with the allowable error of a kilometer and a half, while the error in the spacecraft time of arrival to the specified point in orbit was seven and a half seconds with allowable error of a minute and a half.

Дружеские шаржи А.А. Леонова Дружеские шаржи А.А. Леонова
Friendly caricatures by A.A.Leonov

Light beacons were operating on Soyuz, and, during the rendezvous with the Apollo, orientation side lights were switched on. The light beacons made it possible for the US crew to see the Soviet spacecraft from the distance of several hundred kilometers.

Картина А. Леонова
Painting by A.Leonov

On July 17, at 19 h 12 min. (in the 36th orbit of the Soyuz flight) the docking of both spacecraft was accomplished. Cosmonaut Alexei Leonov describes this event in his book "Solar Wind":

"During the 34th orbit we established direct radio link with the Apollo – at that time the spacecraft were flying over Atlantic Ocean and we were separated by the distance of just 430 kilometers.
- "Soyuz"! - we heard in our earphones the voice of Thomas Stafford who was speaking Russian.
- Good day! How do you read me!
- Read you 4 by 5, hello to everybody! - I answered in English.
The rendezvous is going well. We tightly keep to the assembly orbit. The Apollo is still flying below us. I turn the Soyuz through sixty degrees about the long axis: At the moment of the docking, the Apollo's antennas should be pointed towards the US communications satellite stationed over Kenya, it is via this satellite that the radio and TV broadcasts will be downlinked to Earth.
And the Earth is worried. Valeri maintains a stable link with Moscow, and I work with Apollo and Houston.
- To you Valeri, break a leg, - says our Center.
- And tell the US guys – we keep our fingers crossed.
The distance between Soyuz and Apollo is getting shorter. I established two-way radio communications with Tom.
- Read you 4 by 5, Alexei – says Tom.
- Beautiful picture, - I reply.
- The spacecraft is right at the center.
The Soyuz began its turn about the long axis at 19 hours 04 min and 47 s.- Valeri recorded this time precisely.
The three guiding petals on the docking unit of Apollo find themselves between the petals on the docking unit of Soyuz. After that – a slight push and a signal on the instrumentation panel: "Capture" Hard mate. The docking is complete! Vance Brand reports that he switched on the retraction mechanism. With a 20-ton force Soyuz and Apollo formed a new strong house in space.
The time is 19 hours 9 minutes. The docking occurred three minutes ahead of schedule. Tom's "reckless driving"? Shift flight director V.Blagov is laughing:
- We have managed to convert Stafford. The docking was soft.

After that, there was the famous handshake in space.

Т. Стаффорд и А. Леонов: рукопожатие в космосе
T. Stafford and A.A. Leonov: handshake in space

The crews paid visits to each other. First, the Soyuz was visited by Thomas Stafford and Donald Slayton.
They signed a document about the first international docking in space and put commemorative medals together from their halves, which each crew had brought from Earth.
In the mean time, Valeri Kubasov went to Apollo to visit Vance Brand. They conducted a joint scientific experiment in welding called "the universal furnace". On the next day, July 18, 1975, when A. Leonov visited Apollo, together with Tom he assembled from small metal plates two memorial plaques depicting national emblems of USSR and USA. Each of these plaques carried the date of the spacecraft docking.
The successful docking validated the engineering solutions developed and implemented in creative cooperation between Soviet and US scientists, designers and cosmonauts. It could be said that Apollo-Soyuz became the prototype for the future international space stations.

Эмблема программы ЭПАС
ASTP mission patch

Схема полёта космических кораблей по программе ЭПАС
The spacecraft flight profile under the ASTP program

Схема полёта космических кораблей по программе ЭПАС  (рис. из Музея истории космонавтики, г. Калуга)
The spacecraft flight profile under the ASTP program
(diagram from the Museum of Space History, Kaluga)

On July 19, during the 64th orbit of Soyuz the spacecraft undocked, during the 66th orbit the spacecraft docked again. The final undocking of the spacecraft took place during the 68th orbit, after which they flew under their individual programs:

  • On July 21, 1975, the descent vehicle of the Soviet spacecraft landed 54 kilometers to the north-east of the town of Arkalyk;
  • On July 25, the US spacecraft splashed down in the Pacific Ocean about 600 kilometers from Hawaiian Islands.

The total flight time of Soyuz-19 was 5 days 22 h 31 min, the total flight time of the Apollo was 9 days 1 h. 28 min, the total time the spacecraft spent in the docked state was 46 h. 36 min.


The following scientific research and engineering experiments were conducted in the course of the joint flight:

  • «Artificial Solar Eclipse» - study solar corona and spacecraft induced atmosphere conducted from Soyuz when the Sun was eclipsed by Apollo;
  • «Ultraviolet Aabsorption» - measuring concentration of atomic oxygen and nitrogen in space at the flight altitude;
  • «Zone-Forming Fungi» - a study of the effects of space environmental factors – zero gravity, g-loads, space radiation – on basic biological rhythms;
  • «Microbial Exchange» - a study of exchange of microorganisms in spaceflight environment between crewmembers and crews of different spacecraft;
  • «Universal Furnace» - investigating effects of zero gravity on certain metallurgy and crystal chemistry processes in metals and semi-conductor materials, etc..

As early as July 15, A.A. Leonov and V.N. Kubasov began biological experiments, including experiments on seeds of various plants and small aquarium fish Danio rerio. By that time a similar work had already been done onboard Soyuz-16 by Anatoly Filipchenko and Nikolai Rukavishnikov, and now it was important to compare results.
Altogether, 34 experiments were conducted under the program, out of which: 5 joint experiments, 6 Soviet experiments, and 23 US experiments.
The five joint experiments were dedicated to the study of the chemical composition of the atmosphere, biology, Solar studies and conducting technical process in space – developing new materials and alloys in zero gravity (cosmonauts placed samples of various metals into an electric smelting furnace onboard Apollo). The six Soviet experiments dealt with astrophysics and biology. The US astronauts conducted research in the fields of studies of Earth resources, geology, atmospheric contamination, astronomy, biology and metal working.
Many of these experiments had been conducted before. But the ASTP program used new methods in Earth studies from space, in living cell studies, in search for ultraviolet radiation sources.

Some of the technical features

In the ASTP program Apollo was given the active role - to chase Soyuz and rendezvous with it, а "Союз", while Soyuz which had gone into orbit earlier to establish the assembly orbit, send its parameters to Apollo and wait for it. This was due to the fact that the US spacecraft had a larger supply of propellant (and that was one of the reasons why the US spacecraft was larger).

Looking at the mockup of the docked spacecraft on display at RSC Energia museum (a picture at the end of the article), one can clearly see that Apollo dimensions are much larger than those of Soyuz, so one might think that the Soviet spacecraft has a smaller internal volume and is less comfortable. However, that's not so. The free volume of Soyuz habitable modules is 6.5 m3; while the free volume of the Apollo crew cabin is 6.1m3 + volume of the transfer compartment. Thus, these are comparable values. According to A.Leonov's memoirs, the "two-room" Soyuz configuration also has its pluses from the standpoint of everyday activities: The Soyuz layout was much better thought out and much more comfortable than that of Apollo. The Americans enjoyed their visits to the Soviet spacecraft.

There were some unforeseen situations. Thus, on Soyuz the TV equipment went "blind" before the launch, while on the US side during the flight the docking assembly could not be dismantled due to an installation error on one of the hatches of the transfer airlock. The transfer between the spacecraft was at stake.
On the ground the specialists rushed to study the causes of the malfunctions. The situation with the TV equipment cleared up quickly – the fault was found in the unit which was to switch to the onboard transmitter different TV cameras located inside the spacecraft. It was decided to circumvent the failed section of the device and connect the color TV cameras directly to the transmitter. The commander of the backup crew V. Dzhanibekov did all this work on the ground and sent his recommendations to orbit. The repairs were done very quickly. And instead of electrician's tape, which was not available onboard, the cosmonauts used a band-aid.
The Americans also managed to repair their hatch after consultations with the ground.
There were also other surprises. During the re-docking, when Soyuz was the active vehicle, during retraction of the spacecraft after capture, the Apollo pilot suddenly thought that his spacecraft lost its alignment. He gripped the joystick and "corrected" the alignment. And Soyuz at that moment was hanging on extended shock-absorbing rods. Angular loads were generated, Soyuz began swaying to and fro on the shock absorbers, there was a grating sound, but the structure survived. The retraction was complete and the docking accomplished. The protocol had provisions for this – it was forbidden to fire thrusters during retraction. The subsequent investigation showed that the loads on the shock-absorbing rods exceeded design values but the rods held. And had they not held, everybody would have said afterwards that Soyuz docking mechanism broke during retraction. And shifting the blame on Apollo would have certainly looked in the eyes of the public as a lame excuse. This story didn't end here – during the final session the Soviet side demanded explanation. In the end, the Americans had to apologize.
During Apollo landing, due to the astronauts' error an automatic program was not switched on, parachute deployment and attitude control thrusters shutdown were performed manually at the altitude of 2.5 km. At that time, the reaction control thrusters continued to operate even after the air valve was opened, trying to cancel the natural swaying of the descent vehicle under the parachutes. In the process, the oxidizer vapors (poisonous nitrogen tetroxide) from the descent thrusters found their way into the crew cabin. After the shutdown of the automatic descent system, the reaction control thrusters finally shut down too. Upon splashdown, the descent vehicle capsized. D. Slayton and V. Brand lost consciousness. Fortunately, T. Stafford responded promptly, he managed to unfasten his safety harness, break out oxygen masks and put them first on himself, and then on the rest of the crew. According to physicians' estimates, the astronauts' exposure to the toxic substance was about three fourths of the lethal dose.

В. Бранд, Т. Стаффорд, А.А. Леонов, В.Н. Кубасов и Д. Слейтон  у макета орбитального комплекса "Аполлон" - "Союз"
V.Brand, T.Stafford, A.A.Leonov, V.N.Kubasov and D.Slayton
in front of a mockup of the orbital complex Apollo-Soyuz 


The joint mission of manned spacecraft Apollo and Soyuz became an important milestone in the development technical cooperation and direct contacts between the two former rivals in space. The joint experiment was of great scientific importance. So what is the scientific heritage from the joint mission? That's how this question was answered by one of the participants in ASTP program, researcher at NASA Dr. Thomas Julie: «It left enough scientific materials to occupy hundreds of scientists all over the world for quite some time».
But, regardless of a fairly large amount of obtained scientific and technical data, the greatest significance of the ASTP lies in the political domain. This program demonstrated that the leading space powers can put aside their political and economic differences and work together.
Several options were proposed for continuing the joint work. NASA had an inventory of unused spacecraft and launch vehicles, there was a project to launch Skylab 2 and dock to it spacecraft from the two countries. However, for all kinds of reasons, these plans were scrapped. The next joint mission of Russian cosmonauts and US astronauts took place only in 1994.

In conclusion

After the mission, the crews continue to keep in touch, they became friends.
In 2005, S.P. Korolev Rocket and Space Corporation Energia held a meeting with participants of the Apollo-Soyuz program. The Corporation president welcomed at RSC Energia Russian cosmonauts A.A. Leonov and V.N. Kubasov (the crew of Soyuz-19), US astronauts T.P. Stafford and V.D.Brand (crewmembers* of Apollo-18), as well as managers and leading specialists of the company who worked under this international program.

В музее РКК "Энергия" у макета состыкованных кораблей "Аполлон" и "Союз", 2005 г.
At the RSC Energia museum in front of the mockup of docked Soyuz and Apollo spacecraft, 2005.
Standing at the center in black suits are crewmembers and president of RSC Energia N.N.Sevastianov.
The rest are participants in the project, managers, technical specialists. In the rear on the right side is the actual descent vehicle of Soyuz-19 autographed by the crew 

Participants in the meeting underlined the historic significance of the ASTP program, which opened the door to cooperation between the world's two leading spacefaring nations in peaceful space research and exploration with the use of manned spacecraft. They noted that the Apollo-Soyuz complex construction and two-day flight in orbit which occurrd as a result of the docking between Soyuz-19 and Apollo-18 became the prologue to the new joint programs in 1990s – Mir-Shuttle and Mir-NASA, which became the foundation of the current ambitious project of the International Space Station.
Cooperation in space continues regardless of any political confrontations on Earth.

*) D. Slayton died in 1993, and V.N. Kubasov passed away in 2014








Международная космическая станция Автоматические космические системы logo fka eng baner rsc-eng "Морской старт" и "Наземный старт" "Морской старт" и "Наземный старт"