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 Center.

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 (see below).

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 bio-mass. Medical tests were also carried out, including experiments to measure blood flow to the brain.

The crew landed in a heavy snowstorm on 26 December, but were recovered a few minutes later, some 200 km southwest of Karaganda.

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 1,000 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 UV 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.

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