Isso soa um pouco como The Dark Beyond the Stars de Frank M. Robinson. Um ótimo livro!
De Wikipedia :
The story is told through the narrative of Sparrow, a crew member aboard the Astron, which is a multigenerational starship sent from Earth on a search for life on other planets throughout the Milky Way. Sparrow fell off a cliff during one planetside excursion and is stricken with amnesia. No one will discuss his past with him and the computer has restricted his data, reasoning that he should "look within" to fully recover. Sparrow struggles to revive his memory and familiarizes himself with the Astron, the crew, the enigmatic Captain Kusaka, the state of the ship and its mission; in which the search for life has lasted over 2000 years with no success.
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Most members of the crew know that they will not survive the journey since it would take several centuries to cross and the ship would not make it with its current rate of attrition of their closed ecological system. But Captain Kusaka, who is immortal and obsessed with exploration, does not heed to the warnings and will do whatever it takes to complete the mission. As a result, the crew secretly try to plan a mutiny to seize control of the ship and return to Earth, the only place they know that harbors life.
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Things change when Sparrow slowly discovers that he is also immortal like the Captain, and that he has lived previous "lives" on the ship as the same man but with different names and his memories of every previous identity are erased every generation by orders of the Captain.
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[He] takes command of the Astron and sets a course back to Earth, which takes 20 generations (400 years) to reach.