the name of a series of Soviet spacecraft designed for orbital flights around the earth; also, the program for the development and launching of these spacecraft, which began in 1967. Soyuz was intended to solve a broad range of problems in near-earth space: to refine autonomous navigation, control, rendezvous, and docking techniques; to test the design and maintenance principles of space stations; to study the effects on the human organism of extended spaceflights; to test the feasibility of using piloted spacecraft to study the earth in the interests of the national economy; and to conduct technical and scientific experiments in space.

Principal specifications. The maximum weight of the Soyuz spacecraft is 6.8 tons, the maximum length is 7.5 m, and the maximum diameter is 2.72 m. The diameter of the living compartments is 2.2 m, the span of the solar battery panels is 8.37 m, and the total volume of the living compartments is 10 m³.

A Soyuz spacecraft comprises three basic compartments (Figure 1), which are linked mechanically by means of explosive bolts. The spacecraft is equipped with an orientation and flight control system used in space and during reentry; an engine system for mooring and orientation; a rendezvous-vernier engine; systems for radio communication, electric power, docking, and radio guidance and for rendezvous and mooring operations by means of optical devices; a soft-landing system; life-support systems; and a control system for the onboard apparatus and equipment.

Basic compartments. The reentry compartment is used for crew seating during orbital insertion, flight control operations in orbit, controlled reentry into the atmosphere, parachute deployment, and landing. It is a hermetically sealed compartment, with two side observation windows and one window fitted with an optical orientation sight. The housing has an external heat-resistant covering and an internal heat-insulating and decorative skin. It contains the cosmonaut’s console, the spacecraft’s control sticks, instruments and equipment for the main and auxiliary systems, containers for returning scientific apparatus, and reserve stores for the crew, such as equipment, foodstuffs, and medicine. Provisions are made for a control panel for compatible radio equipment operating on identical frequencies and external lights for the Apollo-Soyuz mission. Special lamps and extra mountings for television cameras are installed for color television transmissions to earth.

The orbital module is used as a working compartment for carrying out scientific experiments, for the relaxation of the crew, and for crew transfer to another spacecraft. It consists of two hemispherical shells connected by a cylindrical insert and has three viewing windows, one of which is located in the cover of the transfer hatch of the docking unit. There is a connecting hatch to the reentry compartment in the lower section of the orbital module and a side hatch for crew entry on the launch pad. The orbital module has a control panel, instruments and equipment for the main and auxiliary systems, and scientific apparatus.

The instrument and propulsion unit is designed to house the main apparatus, equipment, and systems for orbital flight. It consists of intermediate, instrument, and propulsion sections. The intermediate section has a truss framework and joins the reentry compartment with the instrument section. It has ten mooring and orientation engines with a thrust of 100 newtons (10 kilograms-force) each, fuel tanks, and a feed system for the monopropel-lant. The instrument section is hermetically sealed and has the shape of a cylinder with two end plates. The instruments it houses are for the orientation and flight control system, the onboard complex of apparatus and equipment, the radio communications system and the time-programming device, radio telemetry, and the common electric power supply. The propulsion section is in the form of a cylindrical shell that is joined to a conical shell that terminates in the base frame, which is designed to mount the spacecraft on a launch vehicle.

Located on the outside of the propulsion section are the large heat exchanger for the temperature-control system, four mooring and orientation engines with a thrust of 100 newtons each, eight orientation engines with a thrust of 10 newtons (1 kilogram-force) each, and the lower attachments of the solar batteries. Inside the propulsion section is the rendezvous-vernier engine unit, comprising main and backup engines having a thrust of 4 kilonewtons (400 kilograms-force) each, fuel tanks, and a system for feeding the bipropellant.

The radio communication and telemetry antennas, ion sensors

Figure 1. General plan of the Soyuz 19 spacecraft: (a) side view, (b) plan view; (1) two-way docking collar, (2) ultrashort-wave antennas (121.75 megahertz), (3) antennas for the radio-television system, (4) orbital module, (5) reentry compartment, (6) navigation lights, (7) mooring and orientation engines, (8) flashing beacons, (9) solar orientation sensor, (10) instrument and propulsion unit, (11) orientation engines, (12) radio telemetry antennas, (13) antennas for communication with earth, (14) rendezvous-vernier engine, (15) orientation ion sensor, (16) solar battery panels, (17) antennas for the radio command link and trajectory tracking, (18) orientation sight, (19) windows, (20) hatch for crew entry, (21) antennas for the ultrashort-wave Apollo radio system (259.7 and 296.8 megahertz)

for the orientation system, and part of the battery system for the spacecraft’s common electric power supply are mounted in the area of the base frame. The solar batteries are in the shape of two wings, each having three panels. The radio communication and telemetry antennas and the colored navigation lights are mounted on the end panels of the batteries.

All the spacecraft’s compartments are covered on the outside with green combination shield and vacuum thermal insulation. During that portion of orbital insertion that takes place in the earth’s dense atmospheric layers, the spacecraft is shielded by a releaseable nose fairing equipped with the power unit for the emergency escape system.

The docking gear is installed for one-time use when a Soyuz spacecraft is used as a transport vehicle. It performs several functions: it absorbs, or damps, the collision energy of the two spacecraft, serves as the primary coupler, aligns and links up the spacecraft, couples the spacecraft structures rigidly, forms a hermetically sealed joint, and undocks and separates the spacecraft. Its structure comprises two parts: an active docking assembly, which is mounted on the transport vehicle and is equipped with a mechanism for performing all docking operations, and a passive docking assembly, which is mounted on a space station or another spacecraft.

Each part of the docking gear is in the form of two independent subassemblies: the docking mechanism on the active assembly (and its reciprocal part on the passive assembly) and a docking frame with additional mechanisms. The docking mechanism on the active assembly performs the principal functions in joining the two spacecraft until the docking frames touch each other. The reciprocal passive part is a receiving cone, in which the probe on the docking mechanism enters during docking.

In an experiment for the Apollo-Soyuz mission, a test was made of a two-way docking collar that was new in principle and technically more developed. The characteristics of the new docking gear are different from those of all the previous probe-and-cone designs which both Soviet and American spacecraft have used heretofore.

Principal systems. The spacecraft’s orientation and flight control system is designed to control the craft’s position in space. It controls the craft as the craft assumes various attitudes, maintains the attitudes over periods of time, stabilizes the craft when a reaction impulse from the rendezvous-vernier engine is registered, and controls the rendezvous process with another spacecraft. The system can operate either in an automatic mode or under manual control. The onboard apparatus is powered from a central electric power supply system with solar batteries having an effective area of 14 m². After the spacecraft has docked with a space station, the batteries are used in a common power supply system.

The life-support systems include a regeneration system for the atmosphere in the reentry compartment and orbital module, food and water supplies, and a sanitation-hygiene module. Regeneration is provided by means of substances that absorb carbon dioxide and simultaneously liberate oxygen. Special filters absorb harmful contaminants. The crew members work in protective suits during orbital insertion, docking and undocking, and descent from orbit. During the other parts of a flight, the suits are stored in the orbital module, packed in flight bags. When the suits are being worn, work conditions are maintained by ventilation of the suits with cabin air from the ventilation equipment in the reentry compartment.

The complex of radio-engineering equipment is designed to determine the spacecraft’s orbital parameters, receive commands from the earth, provide two-way telephone and telegraph communication with the earth in various wave bands, and transmit to earth television images of the interior of the modules and of the exterior as observed through the windows.

The temperature-control system maintains the air temperature in the living compartments within the range of 15° to 25°C and the relative humidity within the range of 20–70 percent. The air temperature in the instrument module varies from 0° to 40°C.

Launch data. Between 1967 and 1975, 18 piloted Soyuz spacecraft were launched into earth orbit (Table 1). The Soyuz 4 and Soyuz 5 spacecraft achieved an automatic rendezvous, and the two piloted spacecraft were moored and docked manually to form the first experimental space station, with a total mass of 12,924 kg. After the docking, A. S. Eliseev and E. V. Khrunov went out into space in space suits and transferred from one craft to the other. Soyuz 6, Soyuz 7, and Soyuz 8 completed a group flight during which a program of scientific and technical experiments was conducted, including tests of methods for welding metals under conditions of high vacuum and zero gravity. Navigational observations and group maneuvering were also conducted. The spacecraft coordinated with one another and with earth command and tracking stations to achieve simultaneous flight control for all three spacecraft. Soyuz 9 completed a flight of 424 hr, marking the beginning of the development and testing in space of the equipment required for extended spaceflights without the creation of artificial gravity on board the spacecraft. An Orion 2 telescope system installed on board Soyuz 13 was used to conduct astrophysical and spectrographic observations of sections of the heavens in the ultraviolet region of the spectrum. During the flights of Soyuz 1, 3, 10, 11, 12, 14, and 15, operation modes were refined for the onboard apparatus, and tests were made on new and improved systems both in solo flights and joint flights with Salyut space stations.

Several unmanned Soyuz spacecraft were launched for the purpose of improving the spacecraft’s design and onboard systems. Two flights of unmanned Soyuz spacecraft were made (Cosmos 638 on Apr. 3, 1974, and Cosmos 672 on Aug. 12, 1974) in accordance with a Soviet program of preparation for the joint So-yuz-Apollo mission. From Dec. 2 to 8, 1974, a flight was made by A. V. Filipchenko and N. N. Rukavishnikov on board Soyuz 16. The spacecraft was similar to the Soyuz 19, in which the Soyuz-Apollo mission was completed. Tests were conducted of the onboard systems, which had been updated to meet the requirements of the joint flight. These systems included a new docking apparatus, new orientation and propulsion control systems, and new life-support systems. Trials were also conducted on the operation modes of the onboard apparatus and on the ability of the crew to solve problems identical to those that might be encountered during the joint flight.

The Soyuz 17 and Soyuz 18 spacecraft were used for two flights to the space station Salyut 4. During these extended spaceflights, lasting approximately 30 and 63 days, respectively, an extensive series of studies of the sun, planets, and stars was conducted over a broad spectral range of electromagnetic radiation. On Soyuz 18 the first complex photographic and spectrographic study was made of auroras and of noctilucent clouds—a rare phenomenon of nature. Comprehensive research was conducted on the reaction of the human organism to the effects of an extended spaceflight. Tests were also conducted on various methods of preventing the undesirable effects of weightlessness. An independent part of the flight program of Soyuz 18 were technical experiments for the development of new systems and instruments for future spacecraft and long-term space stations.

During the flight of Soyuz 19, conducted in the Soyuz-Apollo program, the two spacecraft docked twice (on July 17 and 19, 1975), and five joint scientific and technical experiments were performed: an artifical solar eclipse, an ultraviolet absorption experiment, an experiment with zone-forming fungi (Actinomyces levons), an exchange of cultures of microorganisms, and a test of a general-purpose furnace. The realization of the joint Soviet-American experiment was an important step in the development of international cooperation for the study and exploration of space for peaceful purposes.