But when they prepare for these journeys, one added challenge faces them: How should they handle their period?
"When women first went into space, it wasn't known what the effects would be," said Varsha Jain, gynecologist and researcher at Kings College London
, who was among the authors of a recent paper
on menstruation in spaceflight.
It turns out that while most systems in the human body are heavily affected during spaceflight, the female menstrual cycle doesn't seem to change at all.
"It can happen normally in space, and if women choose to do that, they can," Jain said.
A few waste-disposal facilities on board the international space station can handle human blood but were not originally designed to do so, according to Jain. A further practical issue of women having their period in space is the added weight and calculations of taking items such as tampons and sanitary towels.
Astronauts at NASA undergo individual assessments tailored to their needs, mission duration and physiology, according to a spokesman. "Protocols allow for several choices, the individual treatment selected for any particular astronaut is a private matter between the astronauts and their flight surgeon."
In reality, extensive practicalities aren't really a concern. Most women opt instead to use contraceptives and put their periods on hold, both in preparation for and during spaceflight, as highlighted in the paper
by Jain and her colleagues.
"NASA flight surgeons are finding female astronauts just don't want to have to deal with their periods," Jain said.
When the space shuttle was in operation, missions would take a few weeks on average, enabling astronauts to use oral contraceptives to time their cycles accordingly, but missions to the International Space Station can last for up to six months, and any mission to Mars could involve journeys of up to three years -- putting periods on hold for much longer periods of time.
What are the risks?
"No research has been done on long-term use of contraceptives in space," Jain said. "What we do know from long-term use on Earth is, you can take it back to back for many years."
The evidence is fairly strong for the 3 billion-plus women here on Earth, but while Jain's team is eager to stress that these risks remain low when in space, the studies backing this up are hard to come by, mainly because the numbers available to study on are so few.
The paper highlights the now-common use of the combined oral contraceptive pill among female astronauts. "[These] have been used for a number of years," Jain said.
But with a mission to Mars likely to take years, the question of payload could come back into play due to the weight of the many pills required for the journey: an estimated 1,100 pills, according to the paper.
Instead, Jain is drawing attention to the now widespread use and availability of more longer-lasting options, known as long-acting reversible contraceptives, which are thought to be a safe and reliable alternative, in terms of both health and waste. "[There is] no packaging to dispose, and they dispel concerns regarding stability during storage," the authors write.
"This is the first time we can say these options are safe to use and available," Jain said.
Previous concerns about health risks in general related to factors such as exposure to radiation when in space and risk of blood clots during spaceflight, but anecdotal evidence from missions has revealed no such risks in practice.
"No one has experienced anything," said Virginia Wotring of the Center for Space Medicine at the Baylor College of Medicine, who co-wrote the paper.
She stresses that there is, however, evidence against myths of blood flow reversing when women have their periods in microgravity. "That has long been debunked," she said.
The benefit of bone density
Taking the birth control pill, however, could in turn provide some benefits for female astronauts on their return to Earth. "It could potentially be advantageous," Jain said.
The benefit comes down to one of the key physiological challenges facing all astronauts -- male and female -- who spend extended periods of time in microgravity: their bone density.
"The lack of gravity means astronauts lose bone mineral density," Jain said. This happens as there are no loads acting on the bone to strengthen it. "And what we do know is that estrogen can help with density."
Estrogen is a key ingredient of the birth control pill, and its use could therefore be putting females at an advantage during space missions. The hormone is, however, lacking from the longer-acting contraceptives.
"Estrogen is protective of bone," Wotring said. "[So this] could reduce loss."
Wotring plans to investigate this further but in the meantime will be working with female astronauts to keep their cycles primed, wherever they are in the universe.