Why Women’s Bodies Are Better Suited for Space Travel

Women’s bodies and minds are uniquely well-suited to the rigors of space flight

Illustration: Tess Smith-Roberts

TThe recent all-women’s space walk on Oct. 18 was hailed as a feminist milestone and precursor to NASA’s Artemis lunar exploration program, which aims to put the first woman on the moon’s surface by 2024. But at the end of the day, it was just two women doing their jobs — in this case, replacing a battery unit on the International Space Station (ISS).

Women’s bodies and minds are uniquely suited for space missions. They’re physically more efficient in many ways, and mentally hearty.

After the 2024 Artemis endeavor comes something even more ambitious: NASA aims to land humans on Mars by 2033. Considering the intense physical and psychological demands that will come with this perilous voyage, an all-women mission could be the ticket. “When I give presentations, we talk about the first man on the moon, and we flip that when we talk about Mars — maybe the first boot print on Mars will be a woman’s,” says Kristin Fabre, PhD, a senior innovation scientist at the Translational Research Institute for Space Health, which works with NASA.

And yet, while astronaut training classes today are often 50% female, only 11% of the astronauts who have made it to outer space so far have been women. The reasons for that have nothing to do with women’s qualifications and capabilities.

How women have been kept out of space

In the late 1950s, when the U.S. space program was ramping up, aerospace engineers began using detailed health data from armed services divisions to create physical fitness guidelines for pilots. According to Margaret Weitekamp, chair of the space history department at the Smithsonian National Air and Space Museum, women’s health data was ignored during the creation of the guidelines. The “absence of a physiological baseline [for women] shamed no one. Aerospace scientists simultaneously declared women to be too complicated and largely irrelevant,” writes Weitekamp in her book Right Stuff, Wrong Sex: America’s First Women in Space Program.

Add to this the lack of basic equipment: Back in 1960, aerial acrobatics pilot Betty Skelton was featured in a Look magazine photo essay titled, “Should a Girl Be the First in Space?” She underwent the same physical-readiness and stress tests as the men, but she had to do it while wearing a belted and rolled-up-at-the-ankles flight jumpsuit, because there were none available to fit her small frame. Before the recent all-woman space walk on October 18, a previously scheduled space walk a couple months earlier was canceled when it was discovered that there weren’t enough space suits in the correct sizes for three women to go outside the ISS at the same time.

Beyond the ignorance of women’s bodies and lack of equipment, there’s long been a societal “concern” over women’s safety in space. The post–World War II era is when “the social and political importance of protecting white married women’s lives led to some of the most restricted cultural gender roles that we’ve seen,” Weitekamp tells Elemental. NASA worried that women involved in the space program would be seen as “frivolous,” and the agency was also concerned that “a woman being injured and killed would be enough to pull the plug on the whole program,” Weitekamp says.

“We are already in a position to say that certain qualities of the female space pilot are preferable to those of her male colleague.”

Dr. William Randolph Lovelace, a NASA contractor, was responsible for testing male astronauts for the Mercury mission. In 1959, he decided to test women, too, and created the privately funded Women in Space Program, which put women through fitness tests for space travel. Some scientific research suggested women might be more efficient astronauts. For example, studies showed women regularly outperformed men in situations that required withstanding prolonged isolation.

In 1960, Lovelace announced that female pilot Jerrie Cobb had passed the astronaut qualifying tests as part of his program. He told a gathering of reporters, “We are already in a position to say that certain qualities of the female space pilot are preferable to those of her male colleague.” In addition to Cobb, 12 other women (out of 19 initial woman candidates) passed the same 87 physical tests as the men did. But the women’s data was never published, because Lovelace’s Women in Space Program never took off and was discontinued.

In 1962, two years before the Civil Rights Act was passed that prohibited discrimination based on sex, Cobb and another female astronaut hopeful, Jane Hart, appeared before Congress to testify that women’s exclusion from NASA was discriminatory. At the hearing, astronaut John Glenn dashed the women’s hopes: “The men go off and fight the wars and fly the airplanes and come back and help design and build and test them,” he said. “The fact that women are not in this field is a fact of our social order.”

Ultimately, President Kennedy wanted a “man on the moon,” and that’s where the priorities, money, and research went. NASA didn’t open the space program to women for almost 20 years after the hearing. In 1983, Sally Ride became the first U.S. woman to go to outer space.

Women’s bodies are made for space

A mission to Mars will be different than any other mission initiated by NASA, as it’s one of the farthest destinations attempted. It’s not just “an extremely difficult engineering challenge,” according to NASA, but one that will require individuals that are highly vetted for health. “You’re looking at probably a three-year mission. And that requires some special people,” Al Holland, a psychologist for NASA, told PBS.

In plenty of important ways, men and women don’t differ much in terms of how they’ve reacted to the physical challenges of spaceflight, including in health impacts like bone density loss, alertness over time, sleep quality, stress, and many others detailed in a 2014 NASA report on the subject. But there are some important ways that women may have the advantage, physically and psychologically.

In any space mission, weight is a concern: Every pound that needs to be lifted into space requires more rocket fuel, and that fuel adds to the ship’s weight. On average, women are smaller and weigh less than men, which translates to less rocket fuel. Women’s bodies are also more efficient. “Men of equal size to women require 15% to 25% more daily calories to maintain their weight,” says Yeral Patel, MD, a regenerative medicine specialist. “Research shows that women lose weight slower on a restrictive diet. Put that all together over a three-year mission, and women’s bodies need significantly less food and oxygen for a mission.”

Fewer calories and oxygen in also means less waste out: “Smaller bodies create and release less waste—both bodily waste and carbon dioxide,” Patel says. Less waste means less stress on shipboard systems and less weight to carry on a multiyear voyage.

Kristin Fabre says that while she doesn’t feel there has been a “true effort to look at sex differences in space,” a woman’s more sluggish metabolism might also be a boon when it comes to having more time to do DNA repair on cells damaged by radiation.

Women have some other advantages over male astronauts: Men’s eyes are affected more by zero gravity. Scott Kelly, who famously spent a year straight living on the ISS, has retinal thickening caused by fluid buildup behind the eye directly attributed that voyage. This issue occurs in women, but much less often. Kelly wrote in his biography, “If scientists can’t figure out what’s causing those eye issues, we just might have to send an all-women crew to Mars.”

Hearing sensitivity, when measured at several frequencies, also declines with age much more rapidly in male astronauts than it does in female astronauts, according to the 2014 NASA report. And in general, women’s immune systems are stronger than men’s, which could help them deal with bugs the crew may bring with them from Earth.

There are some cases where women may be at a disadvantage. For example, female astronauts in space, as on Earth, are more likely to get urinary tract infections (which are treatable with antibiotics). Women are possibly more susceptible to radiation as well, though some researchers think women’s additional fat deposits, especially around the organs, may reduce radiation exposure to vital tissues.

Psychologically, a Mars mission has unique challenges. The two most significant touchstones that help promote an astronaut’s mental health while in space are the abilities to call home and look out a window and see Earth, says Gary Strangman, PhD, an associate professor in psychiatry at Harvard Medical School and an innovation specialist at the Translational Research Institute for Space Health. “For a mission to Mars, both of these opportunities will disappear.”

Earth will be too far away to see from Mars, and “the round-trip communication time to Mars ranges from six to 44 minutes, which means real-time communication becomes impossible and one must resort to text messages, email, or prerecorded video,” Strangman says.

Other earthbound studies have found that men do best in short-term, goal-oriented missions, whereas women perform better over longer missions that may have unexpected challenges.

Some research suggests women may be better equipped to handle these mental health risks. In an examination of journal entries from astronauts who spent time on ISS, a NASA researcher found that men experienced a greater dip in mood during the missions than women. This is an important consideration for such a long trip.

On a trip to Mars, another major psychological stress will come from living in a small space with a small crew. Women may have the advantage here since research suggests they’re generally more comfortable in closer, more confined conditions—or, as early NASA research puts it, women have more “permeable personal space requirements.”

Some studies have looked at Earth-based scenarios that share similarities with a Mars mission to gain a better understanding of what the physical and mental health risks might be. In a study on 348 people in the British Antarctic Survey who stayed through the winter in isolated conditions—20% of whom were female—researchers found that gender was “a statistically significant predictor for good adaptation. Women were more likely to receive an ‘exceptionally well-adapted’ evaluation from their station commanders.” Other earthbound studies have found that men do best in short-term, goal-oriented missions, whereas women perform better over longer missions that may have unexpected challenges.

While women have plenty of psychological advantages, they are also more likely to experience stress and depression as measured by psychological tests (or women may be more comfortable disclosing this information than men). It’s worth remembering that anyone going to Mars will be highly trained and chosen with both physical and psychological strength in mind, and will likely be the result of “hundreds of considerations for assembling a crew,” Strangman says.

Weitekamp says social change will be the most important aspect in determining if we see an all-women’s mission: “I think we would need to be more used to the idea of not doing a women’s mission, but doing a mission that happened to be all women and seeing it as normal.”

AKA The Curious Human. Science journalist & nature nerd w/serious wanderlust. Former geologist. Still picks up rocks. Words in @NatGeo @SciAm @Slate @CNN, here.

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