Soyuz 23 (Russian: Союз 23, Union 23) was an October, 1976, Soviet crewed space flight, the second to the Salyut 5 space station. Cosmonauts Vyacheslav Zudov and Valery Rozhdestvensky arrived at the station, but an equipment malfunction did not allow docking and the mission had to be aborted.^[4]

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Soyuz 23

Commemoration stamp of Vyacheslav Zudov and Valery Rozhdestvensky
Operator	Soviet space program
COSPAR ID	1976-100A
SATCAT no.	09477
Mission duration	2 days 6 minutes 35 seconds
Orbits completed	32
Spacecraft properties
Spacecraft	Soyuz 7K-T No.10
Spacecraft type	Soyuz 7K-T/A9
Manufacturer	NPO Energia
Launch mass	6750 kg [1]
Landing mass	1200 kg
Crew
Crew size	2
Members	Vyacheslav Zudov Valery Rozhdestvensky
Callsign	Радон (Radon - "Radon")
Start of mission
Launch date	14 October 1976, 17:39:18 UTC
Rocket	Soyuz
Launch site	Baikonur, Site 1/5[2]
End of mission
Landing date	16 October 1976, 17:45:53 UTC
Landing site	Lake Tengiz, Kazakhstan
Orbital parameters
Reference system	Geocentric orbit[3]
Regime	Low Earth orbit
Perigee altitude	243.0 km
Apogee altitude	275.0 km
Inclination	51.6°
Period	89.5 minutes
Vimpel Diamond patch Soyuz programme ← Soyuz 22 Soyuz 24 →

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The crew returned to Earth, but landed on partially frozen Lake Tengiz, the first crewed splashdown in the Soviet space program. While there was no concern about any immediate threat to the crew, the capsule sank under the surface of the frozen lake, and recovery took nine hours owing to fog and other adverse conditions. The landing marked the only example of an unintentional splashdown of a crewed spacecraft to date.

Soyuz 23 was launched 14 October 1976 with an estimated 73- to 85-day mission planned aboard the orbiting Salyut 5 space station.^[5] Other sources suggest a 17- to 24-day mission was a more likely intention.^[6] It was the first visit to the station after the sudden termination of the Soyuz 21 mission in August 1976. However, on 15 October 1976, during the automatic approach phase, the automatic docking system malfunctioned before the craft was within 100 metres of the station. Crews were trained for a manual dock, but not for a manual approach.^[5] The mission, accordingly, had to be abandoned.

The craft had only two days of battery power, so systems were powered off, including the radio, to conserve power.^[5] The day's landing opportunity had already passed, so they had to wait for the next day's landing opportunity near the Baikonur Cosmodrome. On 16 October 1976, Soyuz 23 returned to Earth and landed at 17:45:53 UTC, but weather conditions were poor and the cosmonauts experienced an unusual recovery. They landed on a freezing Lake Tengiz (average depth 2.5 m, max depth 6.7 m), at 8 km from shore, in the middle of a blizzard, with fog and temperatures at −22 °C.^[5] It was the first water landing by a Soviet crew.^[6] The capsule was designed to land in any conditions, even in a body of water, so the only concern was the increased difficulty in finding the capsule and crew.^[5][7]

The parachute quickly sank beneath water and dragged the capsule and its crew beneath the surface; in addition an electrical short caused by the water impact caused the reserve parachute to accidentally deploy. The capsule cooled in the freezing water, and the cosmonauts removed their pressure suits and donned their normal flight suits, expecting a quick rescue. The parachutes became waterlogged and pulled the capsule onto its side, preventing the hatch from being opened. The transmission antennas were also under water, so the crew could not communicate with rescue teams. The capsule's beacons could not be seen in the heavy fog, and rubber rafts used to try to reach them were blocked by ice and sludge. Amphibious vehicles were airlifted to the vicinity, but could not reach the capsule owing to bogs surrounding the lake. Accordingly, the rescue was called off until dawn.^[5] The cosmonauts were safe, but they were low on power, so they were forced to shut down everything but a small interior light.

The next morning, frogmen were dropped in by helicopters and attached flotation devices to the Soyuz craft. The capsule was too heavy to be lifted by the helicopter, so it was dragged to shore. The recovery operation had taken nine hours. No attempt was made to open the hatch as the recovery crews assumed the cosmonauts were dead, so they called for a special team to remove their bodies. Eventually, eleven hours after splashdown, the cosmonauts opened the hatch and emerged alive and well, if badly chilled (the interior of the descent module was coated with frost).^[5]

Press releases by Soviet news agency TASS announced that there had been a water landing and that the cosmonauts were recovered safely, but made no mention of the rescue operation involved and the details of it were not revealed until the era of glasnost a decade later.

• Mass: 6,750 kg (14,880 lb) ^[1]
• Perigee: 243.0 km (151.0 mi) ^[3]
• Apogee: 275.0 km (170.9 mi)
• Inclination: 51.6°
• Period: 89.5 minutes

• Splashdown
• List of spaceflight-related accidents and incidents