Last year, Kate Greene and five teammates simulated living conditions on Mars for a NASA-funded project (the experiment actually took place on a volcano in Hawaii). What she noticed while collecting and managing data:
Week in and week out, the three female crew members expended less than half the calories of the three male crew members. Less than half! We were all exercising roughly the same amount—at least 45 minutes a day for five consecutive days a week—but our metabolic furnaces were calibrated in radically different ways. During one week, the most metabolically active male burned an average of 3,450 calories per day, while the least metabolically active female expended 1,475 calories per day. It was rare for a woman on crew to burn 2,000 calories in a day and common for male crew members to exceed 3,000.
Female astronauts, Greene suggests, may simply be more cost-effective than male ones:
The more food a person needs to maintain her weight on a long space journey, the more food should launch with her. The more food launched, the heavier the payload. The heavier the payload, the more fuel required to blast it into orbit and beyond. The more fuel required, the heavier the rocket becomes, which it in turn requires more fuel to launch.
Rachel Nuwer adds:
Greene is not alone in this thinking. Alan Drysdale, a systems analyst in advanced life support and a former contractor with NASA, supports the idea of selecting for astronauts with smaller body sizes, including women. According to some figures Drysdale crunched, the smallest women in the NASA program require half the resources of the largest men, Greene reports. “There’s no reason to choose larger people for a flight crew when it’s brain power you want,” he told Greene.
(Computer-generated image of Mars at the boundary between darkness and daylight via NASA/JPL-Caltech)