Abstract: To better understand the impact of spaceflight on the human body and to prepare for future exploration-class missions, a pair of identical twin astronauts was monitored before, during, and after NASA’s first one-year mission. One twin was onboard the International Space Station (ISS) while the other served as a genetically matched, ground control. Longitudinal assessments included the genome, epigenome, transcriptome, proteome, metabolome, microbiome, and immunome, in addition to measures of …