1962-04-26 USSR Kosmos 4

Kosmos 4 was the first Soviet reconnaissance satellite to successfully achieve orbit. It was a low-resolution reconnaissance satellite based on the Vostok spacecraft used for crewed missions. The satellite's four-day mission aimed to measure radiation levels before and after the U.S. nuclear tests during Project Starfish Prime—a high-altitude nuclear test conducted on July 9, 1962, which was the largest nuclear test in outer space. However, leaks from the oxygen system tanks used for orientation caused Kosmos 4 to return prematurely after three days of operation. For much of its flight, the spacecraft was uncontrollable until it was deorbited and landed by parachute on April 29, 1962. It was subsequently recovered by Soviet forces in the steppe of Kazakhstan.