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| A Soyuz 13 launch cover, postmarked in Moscow with a hand cancel on December 18, 1973, signed by Pyotr Klimuk and Valentin Lebedev. |
Soyuz 13, launched from Baikonur Cosmodrome on December 18, 1973, was a particularly interesting Soviet crewed mission because it was not a space-station expedition. Instead, the spacecraft was specially modified to serve as a manned astronomical observatory, carrying the Orion-2 telescope. The crew consisted of Pyotr Ilyich Klimuk (Commander) and Valentin Vitalyevich Lebedev (Flight Engineer), both were making their first spaceflight.
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| A Soyuz 13 First Day Cover from "KNIGA", postmarked in Moscow with a hand cancel on March 27, 1974, signed by Pyotr Klimuk and Valentin Lebedev. |
The most important feature of Soyuz 13 was the Orion-2 astrophysical observatory. Engineers modified the normal Soyuz configuration by removing the forward docking equipment and installing the telescope package in its place. This allowed the spacecraft to be devoted primarily to astronomical observations rather than rendezvous or docking. The telescope's principal objective was to study stars in the ultraviolet portion of the spectrum, roughly 2,000–3,000 Å. This was scientifically important because Earth's atmosphere absorbs much of the ultraviolet radiation from celestial objects, making observations from Earth difficult or impossible. The mission obtained ultraviolet spectra of numerous stars and other celestial objects, providing information that could not readily be obtained from ground-based observatories. Soyuz 13 was more than an astronomy mission, it combined astronomy, biology, Earth observation and human-spaceflight research in a relatively short autonomous flight.
