Kosmos 300 was the Soviet Ye-8-5 No. 403 lunar sample-return spacecraft launched on 23 September 1969. It reached Earth orbit but the Blok D upper stage failed its second burn for translunar injection because a fuel-injection valve stuck, leaving the payload in Earth orbit; it decayed about four days after launch and was publicly designated Kosmos 300. The spacecraft carried stereo imaging, a remote sample-collection arm, and a radiation detector.
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