2013 marked the first time that women made up 50% of the NASA
astronaut candidate class.
But looking forward, should NASA try to go even higher?
Should the first human Mars mission be all women?
Look, it's no secret that we here at "Space Time"
love the idea of cloud cities on Venus.
But unless our #OccupyVenus Twitter campaign
works miracles, humans will probably
end up going to Mars first.
The question is, which humans?
See, several articles in journals or in the press
have asked whether it might make sense for a Mars crew
to consist mostly or even entirely of women.
It's an interesting proposal that warrants discussion,
but we need to get some facts straight first.
Today, I'm going to review some of the data underlying
the various arguments.
You guys ready?
Let's start with the physiological arguments
for all-female missions beyond Earth's moon.
A lot of us want to become astronauts, but let me tell
you, becoming one is not easy.
Lots of factors disqualify you from NASA
before you even begin including, currently, height restrictions.
You've got to be 4'11 to 6'3.
In all likelihood, scrutiny will be even greater
for the first manned trip to Mars,
because we can't have these pioneers falling apart
200 million miles from Earth.
So physiologically, what's the biggest health concern
for astronauts right now?
Well, according to a 2014 NASA study
that we link in the description, it's not bone loss.
Instead, it's an issue where women
appear to have a big advantage-- vision impairment.
Several male astronauts have experienced
confirmed vision problems, often accompanied
by anatomical changes to the eye,
both during and after space flight.
All of them were in orbit six months or less,
which is a lot less time than the eight
months of zero G in each direction
that you'd have on a Mars mission.
Now, countermeasures are being studied,
but it's tough, because the exact cause of the phenomenon
isn't entirely understood yet.
What we do know is that so far no women have experienced
lasting vision issues.
And since vision is a pretty critical faculty on a Mars
mission, and given the uncertainty about underlying
causes, this might be a major checkmark in the pro-all women
So are there physiological areas where women do worse than men?
Let's look at the same NASA study.
Women are more prone to space motion sickness when they first
hit zero G, but that goes away.
Women get more urinary tract infections,
but that can be treated with antibiotics.
And women faint more easily from standing up too fast
once they get back to Earth, which
may not be as big a deal in Martian gravity-- still
Now, none of these rise to the same mission
critical level as impaired vision.
However, women do have another physiological minus
that does have to be considered-- radiation.
Women have about twice the risk of radiation
induced cancer that men do.
It's why NASA allows women only half
as much lifetime space flight as it allows men.
Radiation would be a big issue for a Mars
mission, no question.
However, given current shielding technology,
even men might exceed the allowed radiation safety
So while it's a negative for women,
radiation risk might be one of those things
that you have to solve for everyone in order
to send anyone.
Anyway, absent to test for or countermeasures
for the vision problems, women may
have a physiological advantage just because of that.
What about psychological suitability?
Well, the same NASA study reports no sex-based difference
in psychology or behavior during spaceflight.
They attribute this to the robust screening and training
that NASA astronauts undergo.
However, other sources and space programs
tend to give women the edge in this category.
For example, the British newspaper "The Guardian"
reported Chinese space officials as saying
that their female astronaut candidates exhibit better
communication skills and adapt better to isolation
than the male counterparts.
Similar results were found during testing of the Mercury
That's a group of women who were put
through the same tests as the male Mercury astronauts
back in 1960.
Incidentally, the story of those women
and the subsequent political battle
to try to have women admitted to the US astronaut corps
It's covered in an episode of the PBS "Makers" series, which
I highly recommend.
There's a link to the video in the description.
Anyway, it looks like women might
have a slight psychological edge on longer duration missions.
But let's suppose that nothing we've said so far were true.
No physiological or psychological edges for women.
There's still another argument for preferring women
to men on longer space missions--
namely that it costs less to send them to other planets.
It's about food.
While you can recycle air and water,
you need to take all the food mass with you
on a trip to Mars.
And that's true even if you manage to grow plants.
Now, it turns out that women need less food
to do the same activity as men, so that
means less mass to transport, less propellant, and thus
Now, this argument has been made many times over the years,
including by some NASA employees.
But it got a lot more attention in late 2014
when writer Kate Greene wrote an article to this effect
Greene was one of six volunteers--
three men and three women-- in the first four months
study at High Seas, a NASA-funded, enclosed, isolated
habitat on Mauna Loa in Hawaii that
simulates aspects of conditions on a Mars mission.
Greene noticed that the women in her cohort consumed about half
as many calories as the men, despite comparable activity
This was consistent with what had
been seen earlier by current and former NASA analysts
that she cites in her article.
But what Greene doesn't give us is an actual numerical estimate
of the savings, so I did some rough math.
Let's consider the long version of a NASA Mars mission.
It would be 910 days round trip with over a year on the Martian
For whatever reason, the calorie requirements
in space and on Earth are basically the same.
So taking into account the water you need to rehydrate the food,
each person would eat about a kilogram of food per day.
That's about 1,000 kilos, or one metric ton,
per person for the round trip.
So how much food mass could you save if you used all women?
Well, the crew would probably be four people,
but let's say six just to high-ball it.
That's six metric tons of food.
I'm assuming our comparison baseline
is three men and three women, replacing
all the men with women.
Since my one kilo a day is an average of both genders
and since we're only replacing the three men with women--
that's half the crew-- you can knock out about a third
of your total food mass.
So our savings would be two metric tons.
So how does that mass savings translate into dollar savings?
To ballpark that you need to work out how much fuel it would
take to get that food from Earth orbit to Mars orbit and back,
and then estimate the cost of getting
the food plus all that fuel off of Earth's surface
to begin with.
Now, I worked out that you need about 50 tons of propellant
to move those two tons of food there
and to bring back the half ton or so you'd
need for the return trip.
Why so much?
Because as you add fuel to move your payload,
you then need to add fuel to move that fuel
and so on and so on-- this is why space flight
costs so much money.
Now, my number is conservative.
I assume that we wouldn't need any fuel for the descent
to Mars, that you'd leave all the food for the return
trip in orbit around Mars, and that you'd leave all your waste
down on the Martian surface.
So what's the dollar savings?
At today's launch prices, it'd be between $0.5 billion and $5
Our 50 metric tons of food plus food fuel
would thus represent around 5% to 7% of the mission mass
and 5% to 7% of the launch cost, which might be 0.5% to 1%
of the estimated total mission budget.
That's not crazy, but it's not entirely negligible either.
Now, granted, launch costs are dropping so these projections
But even if SpaceX manages to get those launch costs to 1/10
of what I've quoted, we're still talking
a savings of hundreds of millions of US dollars
if we sent only women.
So I guess my bottom line question to all of you is this.
Suppose it turns out that by the time we're ready for the Mars
mission we can manage radiation but cannot manage the vision
And suppose that further testing shows
that four to six women locked in a tiny can in a black void
for two to three years would work as a team
with lower risk of flipping out as well as or better
than a mixed sex crew would.
If all that turns out to be true, and taking into account
the cost issues we discussed, should an all-female crew
be given preference for the first Mars mission?
Because remember, the first Mars mission
really needs to succeed.
So it seems, to me at least, prudent to eliminate every risk
that you know about and are able to manage.
But let's see what you guys have to say.
Have at it in the comments, and feel free to point out anything
that I missed or got wrong.
I'll report on the evolving discussion on the next episode
of "Space Time."
Last week we asked what the most realistic artificial gravity
in sci-fi is.
You guys had a lot of really great comments.
If I don't get to yours individually, don't feel bad.
We have limited time.
A lot of you brought up sci-fi series
that I did not mention in the episode.
Let me run through these things in order. "Ender's Game."
I agree that the novel seems pretty realistic,
the movie less so.
But since I don't have any numbers,
I have no way to confirm this. "Interstellar"--
guess what, I haven't seen the movie yet
because I have no life.
But I looked at the specs, and the ship
rotates at five to six RPMs.
You would definitely notice a Coriolis force.
"Rendezvous With Rama," which is another novel
by Arthur C. Clarke.
I agree it has slow RPMs and low Coriolis effects,
but it only has 0.7 earth Gs, which might be intentional.
I don't know.
The "Gundam" anime series-- yet something else I've never seen.
However Scina Bocere pointed out that its design
is based on something called an O'Neill Cylinder that you
can look up on Wikipedia.
And Watchit1337 supplied numbers for the "Gundam" ships, which
if right, I agree would produce minimal Coriolis effects.
Finally, some people brought up using
an accelerating ship in order to get artificial gravity.
So go 9.8 meters per second per second acceleration in one
This is done apparently in "Mass Effect," the "Expanse" series,
another Niven work called "The Mote in God's Eye."
The problem is, where do you get the fuel
to keep that acceleration going?
There's lots of reasons that's not realistic, which
is why I didn't bring it up.
The remaining comments are about things that
happened in the episode itself.
Greg Peden points out that around three minutes, 47
seconds, where we had the ball sort of being thrown away
in the carousel, it shouldn't go as straight
as we had it in the video.
It should tilt slightly to the right because of the already
tangential momentum that it had.
You're absolutely right.
I'm glad you guys picked that up.
Davide Conte asked why we didn't bring up gravity gradient
effects, namely that in a small ring-- this is not as a big
a problem in large rings-- there would
be a gravity differential between what you'd feel
at your feet and your head.
I didn't bring this up because we don't entirely
know the effects of that.
There might be fluid redistribution in the body,
and you might get more bone leeching in your neck
because there's less gravity there compressing your spine.
But in the short term, the Coriolis effects
are a lot more significant.
Fortstorm asks, wouldn't a rotating stations
have trouble turning because its angular momentum vector would
have trouble being shifted?
He's hearkening back to our barrel roll episode there,
and the answer is yes.
That's why O'Neill Cylinder, which I've already referenced
in the comments, would have two counter-rotating sections, so
that there would be gravity here and gravity here
but no net angular momentum, and thus no net gyroscope effects.
Thomas Archuleta points out another scene from "Babylon 5"
that I remember in which Michael Garibaldi drives a motorcycle
at a pretty fast clip but doesn't seem to have
any weird Coriolis effects.
The reason is that if he's driving
along the axis of the space station,
there would be no Coriolis effects.
The Coriolis effects would only be there
if you move along the rim, not along the axis.
CGIAgent asks, in a rotating ship like "Babylon 5," assuming
that you had atmospheric pressure at the rim
and that atmospheric pressure dropped with altitude,
would there be some point near the center of the rim
where the atmosphere got so thin that you'd suffocate
and there'd be a suffocation zone?
I think that would depend on the specs
and how air was being blasted in there.
You might be able to have something on the axis
to sort of inject more air out and artificially increase
the air pressure there.
But I don't actually know.
I'd be really interested if you worked it out.
Finally, John Nielson, who really likes the show,
says he doesn't know what to do with himself.
May I offer the following humble suggestion?
Spread the show.
Tell your friends.
The more people we get watching, the better
we can make "Space Time."