Soyuz 35 ( , Union 35) was a 1980 Soviet manned space flight to the Salyut 6 space station. It was the tenth 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.

Cosmonauts Leonid Popov 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 Vietnamese 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.

Crew

Number in parentheses indicates number of spaceflights by each individual prior to and including this mission.

Launched:

• Leonid Popov (1) - Commander
• Valery Ryumin (3) - Flight Engineer

Landed:

• Valery Kubasov (3) - Commander
• Bertalan Farkas (Hungary) (1) - Research Cosmonaut

Backup crew

• Vyacheslav Zudov - Commander
• Boris Andreyev - Flight Engineer

Mission parameters

• Mass:
• Perigee:
• Apogee:
• Inclination: 51.65°
• Period: 88.81 minutes

Mission highlights

Soyuz 35 ( , Union 35) was the eighth expedition to Salyut 6.

Valentin Lebedev was scheduled to be Leonid Popov’s flight engineer, but he required an operation after injuring his knee while working out on a trampoline. Ryumin, of the last crew to visit Salyut 6, was called in to fill his place. Upon entering Salyut 6, 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, added an storage battery, and replaced air using tanks aboard the Progress 8 supply craft.

On July 19, Popov and Ryumin sent their greetings from the station to the 1980 Summer Olympics, wishing the athletes happy starts in a live communication between the station and the Central Lenin Stadium where the opening ceremony was held. They appeared on the stadium's scoreboard and their voices were translated via loud speakers.

The Soyuz 35 spacecraft returned to Earth carrying the crew launched on Soyuz 36; Popov and Ryumin would return to earth at the end of their six month mission aboard the Soyuz 37 spacecraft.