The experiment was conducted by ESA astronaut Thomas Reiter over the course of five months in 2006. Reiter maintained two cultures of human cells: one free-floating in weightlessness and the other in simulated gravity using a centrifuge. The preserved cells were later examined back on Earth and the weightless cells were in markedly worse shape than the ones kept in simulated gravity. It took some time to sort out, but researchers now think they know what cellular process is being short circuited by weightlessness."
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