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Decades:	2210s - 2220s - 2230s - 2240s - 2250s - 2260s - 2270s
Centuries:	22nd century - 23rd century - 24th century

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The USS Rickover was declared lost with all hands after visiting an area of space near the galactic core that was found to be dense with black holes. A USS Rickover shuttlecraft and half-dead members of the Rickover crew were encountered at the Dyson sphere named Lyra over twenty years later in the 2260s. It was found that the crew and ship had fallen victim to the being known as Ay-nab. ^[1]

↑ TOS novel: "The Starless World" - It was stated that the Rickover went missing "over twenty years" prior to the novel, which took place in the last half of the 2260s.