When Saralyn Mark heard the news earlier this month that NASA was planning the first all-women spacewalk at the International Space Station on March 29, she started to worry. Mark, an endocrinologist by training, was a senior medical advisor to NASA for 18 years. In that role, she studied the way men and women’s bodies differ, on space and on earth. Within the agency, she advocated for spacesuit and technological design that took these differences to account.

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