Soyuz 29

Soyuz 29 (Russian: Союз 29, Union 29) was a 1978 crewed Soviet space mission to the Salyut 6 space station. It was the fifth mission, the fourth successful docking, and the second long-duration crew for the orbiting station. Commander Vladimir Kovalyonok and flight engineer Aleksandr Ivanchenkov established a new space-endurance record of 139 days.

The crew returned in Soyuz 31, which had been swapped by a crew launched in August who returned in Soyuz 29.

The second long-duration mission to Salyut 6 was launched into orbit on 15 June 1978. The space station had been vacant for three months since the record-breaking mission of Soyuz 26 ended after 96 days. The crew successfully docked on 17 June and Kovalyonok and Ivanchenkov reactivated the station. Kovalyonok, who was aboard the failed Soyuz 25 mission to Salyut 6, became the first person to visit the same station twice.

They switched on the station's air regenerators and thermal regulation system, and activated the water recycling system to reprocess water left aboard by Soyuz 26. De-mothballing Salyut 6 occurred simultaneously with the crew's adaptation to weightlessness, and required about one week. On 19 June, Salyut 6 was in a 368-by-338-kilometer (229 by 210 mi) orbit. Onboard temperature was 20 °C (68 °F), and air pressure was 750 mmHg (100 kPa; 14.5 psi). Soon after this, Kovalyonok and Ivanchenkov performed maintenance on the station's airlock, installed equipment they brought with them in Soyuz 29's orbital module, and tested the station's Kaskad orientation system.

The station operated in gravity-gradient stabilized mode between 24 and 26 June to avoid attitude control system engine firings which could cause interference with a 3-day smelting experiment using the Splav-01 furnace. The previous crew installed the furnace in the intermediate compartment so it could operate in vacuum. At the time, the station was in an orbit exposed to sunlight for an entire day. This happened twice a year when the plane of the station's orbit faced the sun.

Soyuz 30, with Pyotr Klimuk and the second Intercosmos participant, Mirosław Hermaszewski of Poland, arrived at Salyut 6 on 29 June. For the third time, the Salyut was a four-man orbiting space laboratory. The activities of the Soyuz 30 crew, however, were severely curtailed so as not to interfere with the Soyuz 29 crew. They returned to Earth in the capsule they came in on 5 July.

Progress 2, the second uncrewed supply tanker to dock with a crewed space station, arrived at Salyut 6 on 9 July. Fifty days of supplies were on board, including 200 litres of water, 250 kg (551 lb) of food, the Kristall furnace, 600 kg (1,323 lb) of propellant, air re-generators, computer sub-systems, replacement parts, film and mail. It took the crew a week to unload the vehicle. On 19 July, the tanker refueled the station, then it was filled with used equipment and trash and sent into a destructive de-orbit on 4 August.

The crew was advised not to use the station treadmill at certain speeds, as dangerous vibrations could be produced. This advice was a result of resonance experiments carried out by the previous long-term Soyuz 26 crew.