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I think this is a short story, I read it 30-40 years ago. A lone astronaut on a space station wakes to find someone bashing on his bedroom door. It is himself from tomorrow, offering to help him repair the space station, which is a two-person job. As the space station travels through the wormhole (I think that term is used), it becomes crowded with other time versions of himself. Does anyone remember the title and/or author?