The lone dedicated Soviet science mission of the year lifted off from Plesetsk aboard a Tsyklon (SL-14) booster. Intercosmos 25 was part of the APEX (Active Plasma Experiment) program to investigate the effects of streams of electrons and beams of plasma on the ionosphere and magnetosphere. The spacecraft was cylindrical, measuring 1.8 m long, 1.5 m in diameter. Eight solar panels extended in petal-like fashion from one end. It weighed about one metric ton at launch. A Czechoslovakian subsatellite, Magion 3, was deployed from Intercosmos 25 on December 28.
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