How space affects women and men differently
Some 564 people have been into space - 65 of them women. That's despite the fact that the first woman in space, Soviet cosmonaut Valentina Tereshkova, went into orbit as early as 1963.
It took Nasa 20 years to catch up and in 1983 Sally Ride became the third woman, and first American woman to go into space. Before her voyage she was asked by the media if she was taking any makeup on her trip and whether she cried when there were malfunctions in the flight simulator.
On Friday 18 October, Nasa conducted its first ever all-female spacewalk, after plans earlier this year were scrapped because of a lack of medium-sized spacesuits to fit one of the astronauts.
For the last decade, Dr Varsha Jain has been working part-time as a space gynaecologist. She combines her PhD work at the MRC Centre for Reproductive Health at the University of Edinburgh with research alongside Nasa into women's health in space.
She's been speaking to Emma Barnett on BBC Radio 5 Live.
Does space affect men and women differently?
VJ: Overall adaptation to the space environment is roughly the same for men and women but there are some differences.
Women are more likely to feel sick when they go into space, men are more likely to get re-entry sickness when they come back to Earth.
Men have more problems with their vision and hearing when they get back from space which women don't get. When women return they do have problems managing their blood pressure so they feel quite faint.
So there are some subtle differences and we don't know if that's to do with hormonal differences or more physiological changes that are occurring. And long-term, understanding those differences will help us understand more about human health on Earth.
What about periods in space?
VJ: When the Americans sent Sally Ride up into space, the questions that Nasa had were about what would happen to women's periods and how do we account for this.
Female astronauts said at the time, 'let's consider it non-problem until it becomes a problem'. But space travel is a bit like a camping trip and the engineers had to plan things like how many sanitary products were needed.
Because it was a very male dominated world, the figures that they thought they needed were 100 or 200 tampons for a week! They shortly came to the conclusion that that many weren't needed.
Most female astronauts now use the contraceptive pill to stop their periods and it is safe for them to do so because they are healthy women.
One of the parts of my work was to research other ways for women to stop their periods to see if things like the contraceptive coil could be more effective.
Why are toilets in space sometimes a challenge for women?
VJ: There are two toilets on the International Space Station, but the engineers hadn't originally accounted for blood.
In space, urine isn't wasted, it's recycled and drinking water is reclaimed from it. Period blood is considered a solid material and none of the toilets on the space station can differentiate solid from liquid material, therefore the water in it is lost and not recycled.
There are also limitations on how water can be used for washing, so the practicalities of personal hygiene while menstruating during spaceflight can be challenging.
Does space travel affect your ability to have children?
VJ: There is no obvious demonstrable effect that going into space has on an astronaut's ability to have children. It is important to remember that both male and female astronauts have successfully had children after spaceflight missions.
However, female astronauts are, on average, 38 years old during their first mission.
This is an area where I think Nasa is leading the way in being a supportive working environment. Ultimately, freezing of eggs or sperm is entirely a personal choice and, as far as I am aware, Nasa does not have any protocols on what their astronauts should do prior to spaceflight missions.
We know astronauts are at risk of radiation in space and we haven't any idea how that will impact a women's fertility.
The quality of sperm and sperm count decreases after space travel, but then sperm regenerates back on Earth, so there is no known long-term damage. Women are born with all the eggs they need for their lifetime, so Nasa is very supportive of female astronauts freezing their eggs before their missions.
How did you become a space gynaecologist?
VJ: My interest in space came before my fascination with medicine. As a child, my brothers were both into Star Trek and seeing strong female characters like Beverly Crusher and Captain Kathryn Janeway really inspired me and shaped my goals.
I knew that I wanted to work in the area of space medicine and because I was practising gynaecology at the time I found a huge knowledge gap in terms of women's health that I thought deserved a platform.
My first day at Nasa, I was like a kid in a candy store. Driving up to the Nasa Johnson Space Centre, the first time I saw the sign I remember screaming because I was so excited. Every single day I remember waking up at 05:00 because I just couldn't wait to get to work.
Would you go into space yourself?
VJ: Not for a long duration mission! I know too much about the physiological changes and that puts me off.
The changes that happen to the human body are like an accelerated aging process. If we take bone changes, astronauts lose bone mass when they go into space and parts of that bone mass are never regained despite the excellent counter measures and programmes the astronauts have when they get back.
Obviously, I would love to see what Earth looks like from space, but long-term as a goal I think I know I'm doing my dream job already.
Dr Varsha Jain was one of the first academic doctors to focus on researching women's health in relation to space. She is currently the 2019 Wellbeing of Women Research Training Fellow at the MRC Centre for Reproductive Health at the University of Edinburgh. investigating why women suffer from heavy menstrual bleeding.
The Emma Barnett show is on BBC Radio 5 Live Monday- Thursday 10:00 - 13:00 BST. Click here to listen to a 5 Live news special on BBC Sounds: The Women of Nasa.