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ring-shaped exterior antenna structure surrounding the forward end of the service module. The instrument-service section had electronic equipment in a lozengeshaped pressurized container, the main propulsion system (“rendezvous-correction power plant. . . with two engines [main and backup]”), docking and orientation engines, the large hull-mounted thermal control system radiator, batteries, and orientation system sensors and antennas. The Soyuz Ferry radio system transmitted and received voice, telemetry, television, and control command communications. Communications were relayed through ground stations and shipborne tracking stations for periods ranging from minutes to tens of minutes. If continuous telemetry were required, onboard recorders could store data for playback when the spacecraft was in range of a surface station. The Soviets also used shortwave frequencies to transmit telemetry data when out of range of a surface tracking facility. Propulsion, orientation, radio, life support, thermal control, electrical power supply, and descent systems were automated (through programtiming devices) and could be controlled from the Flight Control Center (Russian acronym TsUP) by radio. Onboard manual controls were also available. Automatic, TsUP-operated, and onboard manual controls were all part of the onboard complex control system, which included “logical devices, commutators, the electrical automation (for connecting the electrical power supply of the instruments and systems), the control panel, and the command signal devices.” While it was attached to the station, the condition of the dormant Soyuz Ferry was periodically checked by the TsUP and by the onboard crew.

The “orientation and motion control system” (Russian acronym SOUD) included “the infrared plotter of the local vertical” and ion sensors, “gyroscopic angle gauges and angular velocity gauges,” the rendezvous radio system providing relative motion data during rendezvous, optical and television visual orientation instruments, “calculating and commutation instruments,” and manual control and display systems. The most complex SOUD operations involved rendezvous and docking. Feoktistov described the procedure in some detail. At Soyuz Ferry launch, the target Salyut orbited about 350 km high, in an orbit the plane of which passed through Baikonur Cosmodrome, the Soyuz Ferry launch site. Launch occurred as the station passed over the launch site. The ferry was inserted into a 190-200 km by 250-270 km orbit approximately 10,000 km behind the station. The ferry in its lower orbit caught up with the station. Up to four orbital correction burns using the main engine were made to match altitude and speed near the station. When the Soyuz closed to within 25 km of the Salyut, the automatic rendezvous phase of operations commenced. The two vehicles sensed each other and the automatic rendezvous radio equipment (the Igla system) switched on. The spacecraft maneuvered to keep their Igla antennas in line-of-sight so the Soyuz unit could obtain data on range, speed of approach, and orientation. The control computer on the Soyuz Ferry operated the main and docking and orientation engines based on the input data. The automatic rendezvous phase terminated when the distance between the Soyuz Ferry and the Salyut station dropped to 200 to 300 m. At that point the docking phase began. Automatic control could continue up to “mechanical contact of the docking units” of the two craft, or the crew could take manual control

of the Soyuz and dock (Feoktistov asserted that crews were trained for manual dockings, though events seemed to indicate this was not always the case). The main propulsion system propellant tanks used organic film (plastic?) membranes (bladders) to prevent pressurant from mixing with propellant. The system consisted of two engines (main and backup) with 400 kg of thrust each. The backup engine could fire only once, at full power. The attitude control system consisted of 14 10-kg thrust docking and orientation engines and 8 orientation engines with 1 kg of thrust each. The main propulsion system and the attitude control system did not share the same propellant supply on the Soyuz Ferry. The launch control system controlled the descent capsule during return to Earth. Descent attitude control was provided by six engines with 15 kg of thrust each. At 12 km altitude the descent module speed was reduced to 240 m/sec. Parachutes were stored in two separate covered containers. The launch control system controlled the main and backup parachute systems and the landing solid rocket motors. The electrical power supply was based on chemical batteries during autonomous operations. This replaced the solar arrays of earlier Soyuz versions. After docking with the Salyut, Soyuz Ferry systems operated on electricity provided by the station’s solar arrays. The station also recharged the Soyuz Ferry’s batteries while it was docked. Electrical connections between Salyut and Soyuz were maintained through plugs in their docking collars. The thermal control system had two main loops and one auxiliary loop. The two main loops were connected