The two-man crew of Andriyan Nikolayev and Vitaly Sevastyanov broke the five-year-old space endurance record held by Gemini 7, with their nearly 18-day flight.

It tested, for a longer period of time than any other, the capacity of the hardware and the human crew, on the long-term exposure to space conditions and observing (both visually and photographically) geological and geographical objects, weather formations, water surfaces, and snow and ice covers.

The crew conducted observations of celestial bodies and practiced astronavigation, by locking onto Vega or Canopus, and then used a sextant to measure its relation to the Earth horizon.

The pad sustained some damage during a Zenit launch on May 20 due to wind blowing around the rocket's exhaust flames and burning through cabling but repairs were quickly completed.

Another engine burn the night of June 2 placed Soyuz 9 in a 165x153 mile (266x247 km) orbit at a 51° inclination which was considered stable enough to last for the length of the mission.

[6] Commander Nikolayev and flight engineer Sevastyanov spent 18 days in space conducting various physiological and biomedical experiments on themselves, but also investigating the social implications of prolonged spaceflight.

The cosmonauts spent time in two-way TV links with their families, watched matches in the 1970 FIFA World Cup, played chess with ground control, and voted in a Soviet election.

The mission took an unexpected physical toll on the cosmonauts; in order to conserve attitude control gas during the lengthy stay in orbit, Soyuz 9 was placed in a spin-stabilisation mode that made Nikolayev and Sevastyanov dizzy and space sick.

[8][a] It was a consultation game, with the two cosmonauts playing as White and jointly deciding each move, while the two players on Earth did likewise as Black.

The set used aboard Soyuz 9 had pegs and grooves to keep the pieces in place and did not include magnets, which might have interfered with the spacecraft's systems.

[7] At the time the Soviet press reported that this was done to protect the cosmonauts in case space travel had weakened their immune systems.