Soyuz 35 (Russian: Союз 35, Union 35) was a 1980 Soviet manned space flight to the Salyut 6 Space Station. It was the 10th mission to and eighth successful docking at the orbiting facility. The Soyuz 35 crew were the fourth long-duration crew to man the space station.

Cosmonaut and Valery Ryumin spent 185 days in space, setting a new space endurance record. Ryumin had completed a previous mission only eight months before. They hosted four visiting crews, including the first Hungarian, Cuban and Vietmanese cosmonauts.

As long-duration crews now routinely swapped spacecraft with incoming crew, the Soyuz 35 craft was used to return the visiting Soyuz 36 crew to Earth, while the resident crew returned in Soyuz 37.

Soyuz T-2 (Russian: Союз T-2, Union T-2) was a 1980 Soviet manned space flight to the Slayut 6 Space Station. It was the 12th mission to and 10th successful docking at the orbiting facility. The Soyuz T-2 crew were the second to visit the long-duration Soyuz 35 resident crew.

Soyuz T-2 carried Yuri Malyshev and Vladimir Aksyonov into space. A mission lasting under four days, its primary purpose was to perform a manned test of the new Soyuz-T spacecraft.

The launch followed increased recent activity with the uncrewed space station. An uncrewed test craft, Soyuz T-1, spent several months docked to the station until it was undocked 23 March and deorbited 25 March. Progress 8, an uncrewed supply tanker, was launched almost immediately afterwards, on 27 March, and it docked with the rear dock port of the two-dock facility. Several manoeuvres were carried out by 2 April using the Progress to adjust the station's orbit.
Valentin Lebedev had been scheduled to be Popov's flight engineer, but he was disqualified from launch after suffering a knee injury in a trampoline accident. As none of the back-up crew had previous flight experience (required since the failure of the Soyuz 25 mission), Ryumin had been given the choice of replacing Lebedev or delaying the mission. This despite having completed a six-month mission only the previous August. Ryumin's family was upset by this turn of events.
The Soyuz 35 crew docked with and entered the space station on 10 April, using the vacant front port. Ryumin read the traditional note left by the previous crew, a note he had written with no expectation he would be the one receiving it. With Salyut 6 now entering its fourth year in orbit, some signs of wear and tear were becoming evident. Ryumin noted that the two viewports in the transfer compartment had lost their transparency. The windows also had many chips in them caused by micrometeoroids and orbital debris. The cosmonauts replaced components of the attitude control system and life support system, installed a new caution and warning system, synchronized the station's clocks with those in the TsUP Mission Control Center, added an 80 kilograms (180 lb) storage battery, and used Progress 8 to refill the life support system's oxygen and nitrogen tanks.

On 15 April, Progress 8's mission was completed. The crew loaded it with garbage, after which it was undocked and deorbited three days later. Then Progress 9 was launched, docking with the facility on 29 April. The next day, the first-ever transfer of water between a tanker and a Salyut station was completed. Cargo transfers and refuelling operations were completed by 12 May. With this flight, the resupply of the Salyut was complete for the long-duration crew.

Minor repair work was carried out by the crew and "Lotos" was carried out, an experiment involving using special moulds to make plastic items with a quick-setting material. Additional experiments involved production of polyurethane foam, exploring its utility in assembling structures in orbit.