Quote:“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,” Greene said.

That of course means that the same number of female crew members would need far less food to survive than men, which would bring the weight of the launch vehicle down and thereby save money on both food and fuel. On top of that, women are generally smaller and lighter anyway, further reducing blast-off weight.