Soyuz 16 (Russian:Союз 16,Union 16) was a December, 1974, crewed test flight for a jointSoviet-United Statesspace flight which culminated in theApollo–Soyuz mission in July 1975. The two-man Soviet crew,Anatoly Filipchenko andNikolai Rukavishnikov, tested a docking ring and other systems to be used in the joint flight.

Soyuz 16

Mission type	Orbital test flight
Operator	Soviet space program
COSPAR ID	1974-096A
SATCATno.	7561
Mission duration	5 days, 22 hours and 23 minutes
Orbits completed	95
Spacecraft properties
Spacecraft	Soyuz 7K-TM No.4
Spacecraft type	Soyuz 7K-TM
Manufacturer	NPO Energia
Launch mass	6,680 kg (14,730 lb)[1]
Landing mass	1,200 kg (2,600 lb)
Crew
Crew size	2
Members	Anatoly Filipchenko Nikolai Rukavishnikov
Callsign	Буран (Buran - "Blizzard")
Start of mission
Launch date	2 December 1974, 09:40:00UTC
Rocket	Soyuz-U
Launch site	Baikonur1/5[2]
End of mission
Landing date	8 December 1974, 08:03:35 UTC
Landing site	30 km (19 mi) of the northeast ofArkalyk,Kazakhstan
Orbital parameters
Reference system	Geocentric orbit[3]
Regime	Low Earth orbit
Perigee altitude	177 km (110 mi)
Apogee altitude	223 km (139 mi)
Inclination	51.7°
Period	88.4 minutes
Soviet stamp featuring Filipchenko and Rukavishnikov (1975) Soyuz programme ← Soyuz 15 Soyuz 17 →

• Mass: 6,680 kg (14,730 lb)^[1]
• Perigee: 177.0 km (110.0 mi)^[3]
• Apogee: 223.0 km (138.6 mi)
• Inclination: 51.7°
• Period: 88.4 minutes

The Soyuz 16 mission was the final rehearsal and first crewed mission in a program which culminated in theApollo–Soyuz (ASTP) mission seven months later.^[4] TheSoviet Union and the United States,Cold War rivals, had signed severalarms control treaties in the 1960s and 1970s, and had entered into a period ofdetente by the early 1970s. In 1972, a treaty was signed to participate in a joint crewed space flight as a symbol of this detente.^[5]

Early concepts for a joint flight included the docking of aSoyuz craft to the AmericanSkylab space station, or anApollo vehicle docking with aSalyut space station. Once the Americans abandoned their Skylab station in 1974, the Apollo-Salyut concept seemed to be the logical choice, but since the Soviets had started to develop a universal docking adapter for the mission and feared having to publicly reveal details of their military-focused Salyut missions, the two powers opted to link a Soyuz spacecraft with an Apollo spacecraft.^[5]

Three test flights of an uncrewed version of theASTP spacecraft were flown:Kosmos 638, launched 3 April 1974;Kosmos 652, launched 15 May 1974; andKosmos 672, launched 12 August 1974. These three flights, and Soyuz 16, were all launched with an improved version of aSoyuz booster.^[5]

In an unprecedented move, Soviet planners offered to inform theirNASA counterparts of the time of the launch, as long as they did not reveal that time to the press. NASA officials refused to agree to that condition and, accordingly, were informed of the launch an hour after it occurred, on 2 December 1974.^[4]

During the flight,CosmonautsAnatoly Filipchenko andNikolai Rukavishnikov tested the androgynous docking system to be used for the ASTP mission by retracting and extending a simulated 20 kg American docking ring.^[4][5] The crew also tested modified environmental systems, newsolar panels and improved control systems, as well as a newradar docking system.Air pressure was reduced from 760 mm to 540 mm andoxygen raised from 20% to 40% to test reducing the planned transfer time to Apollo from two to one hour.^[5] On 7 December 1974, the docking ring was jettisoned withexplosive bolts to test emergency measures if the capture latches got stuck during the ASTP flight.

The craft landed 8 December 1974, nearArkalyk and was hailed a complete success.^[5] The mission duration, six days, matched the ASTP mission duration to within 10 minutes.^[4]

• Soyuz 16 Diary