Soyuz 13 (Russian: Союз 13, Union 13) was a 1973 Soviet manned space flight, the second test flight of the redesigned Soyuz 7K-T spacecraft that first flew as Soyuz 12. The spacecraft was specially modified to carry the Orion 2 Space Observatory. The flight, manned by Pyotr Klimuk and Valentin Lebedev, was the Soviet Union's first dedicated science mission, and was the first mission controlled by the new Kaliningrad Mission Control Centre.

Launched 18 December 1973, the Soyuz 13 crew of Klimuk and Lebedev performed some of the experiments intended for the failed Salyut space stations from the previous year. Unlike Soyuz 12, the craft was equipped with solar panels to allow for an extended mission. Additionally, an orbital module was attached replacing unneeded docking equipment. This module included the Orion 2 Space Observatory.

The crew used a mulispectral camera to measure the atmosphere and pollution. They also tested the Oasis 2 closed ecology system, and harvested protein, yielding 30 times the original biomass. Medical tests were also carried out, including experiments to measure blood flow to the brain.

The Orion 2 Space Observatory, designed by Grigor Gurzadyan, was operated by crew member Lebedev. Ultraviolet spectrograms of thousands of stars to as faint as 13th magnitude were obtained by a wide-angle meniscus telescope of the Cassegrain system, with an aperture diameter of 240 mm, an equivalent focal length of 1000 mm, and a 4-grade quartz prism objective. The dispersion of the spectrograph was 17, 28 and 55 nm/mm, at wavelengths of 200, 250 and 300 nm respectively. The first satellite Ultraviolet spectrogram of a planetary nebula (IC 2149 in Auriga) was obtained, revealing lines of aluminium and titanium - elements not previously observed in objects of that type. Two-photon emission in that planetary nebula and a remarkable star cluster in Auriga were also discovered. Additionally, comet Kohoutek was observed.

While Americans were following reports about the SL-4 crew at work on Skylab and enjoying their television broadcasts showing their improvised Christmas tree, there was another crew in orbit around the Earth at this time working through Christmas 1973 whose activities received virtually no attention in the West. Soviet cosmonauts Pyotr Klimuk and Valentin Lebedev were launched into orbit aboard Soyuz 13 on December 18, 1973 for the second manned Soyuz flight since the tragic loss of the Soyuz 11 crew who perished in 1971 while returning from their stay on the world’s first space station, Salyut 1. This was the first Soviet space mission to use the then-new Kaliningrad Mission Control Centre which is still used today to support ISS operations.