First, A Bit Of History…

Hundreds of you sent in questions for my live conversation with three astronauts and NASA’s chief scientist on Tuesday. Thanks! The most common question was: “What happens when you get your period in space?”

I didn’t end up asking this question because

a) the question itself has a lot of historical baggage b) the answer is pretty boring

But because people seemed genuinely curious, I decided to answer it here.

First, a bit of history…

In the early days of space flight, menstruation was part of the argument that women shouldn’t become astronauts.

Some claimed (1) that menstruation would effect a woman’s ability, and blamed several plane crashes on menstruating women. Studies in the 1940s (2,3) showed this was not the case. Female pilots weren’t impaired by their periods. But the idea wouldn’t die. In 1964, researchers from the Women in Space Program (4) still suggested (without evidence) that putting “a temperamental psychophysiologic human” (i.e. a hormonal woman) together with a “complicated machine” was a bad idea.

Others raised concerns about hypothetical health risks. They feared that microgravity might increase the incidence of “retrograde menstruation.” Blood might flow up the fallopian tubes into the abdomen, causing pain and other health problems. No one actually did any experiments to see if this really would be a problem, so there wasn’t any data to support or refute these fears.

Advocates for women in space argued that there had been a lot of unknowns when humans first went to space, but they sent men up anyway. Rhea Seddon, one of the first six women astronauts at NASA, recalled during an interview:

We said, “How about we just consider it a non-problem until it becomes a problem? If anybody gets sick in space you can bring us home. Then we’ll deal with it as a problem, but let’s consider it a non-problem.”

Just to give you a sense of the culture surrounding female astronauts back then, here’s an excerpt of a 1971 NASA report about potential psychological problems in space. Researchers Nick Kanas and William Fedderson suggest there might be a place for women in space:

The question of direct sexual release on a long-duration space mission must be considered. Practical considerations (such as weight and expense) preclude men taking their wives on the first space flights. It is possible that a woman, qualified from a scientific viewpoint, might be persuaded to donate her time and energies for the sake of improving crew morale; however, such a situation might create interpersonal tensions far more dynamic than the sexual tensions it would release.

Kanas, now an emeritus professor of psychology at UCSF, told me this was tongue-in-cheek — part of a larger discussion about the problem of sexual desire in space (5). Still, it’s surprising this language was included in an official NASA memorandum. Even advocates for women in space were caught up in this kind of talk. In a 1975 report for the RAND corporation, Glenda Callanen argues that women have the strength and intelligence to become astronauts. But here’s how she begins the report’s conclusion:

It seems inevitable that women are to be essential participants in space flight. Even if they were only to take on the less scientific parts of the space mission, or if they wished only to help “colonize” distant planets, their basic skills must still prepare them to perform countless new tasks.

In a culture where these statements were unremarkable, it’s easy to imagine that questions about menstruation weren’t purely motivated by scientific curiosity.

In 1983, 22 years after Alan Shepard became the first American to go to space, Sally Ride left earth’s atmosphere. She told an interviewer:

I remember the engineers trying to decide how many tampons should fly on a one-week flight; they asked, “Is 100 the right number?” “No. That would not be the right number.”

So what DOES happen when you get your period in space?

The same thing that happens on Earth! In the last three decades of female space flight, periods in space have been normal — no menstrual problems in microgravity.

Notes:

RE Whitehead, MD. “Notes from the Department of Commerce: Women Pilots.” The Journal of Aviation Medicine 5 (Mar-Dec 1934):48.

RS Holtz, MD. “Should Women Fly During the Menstrual Period?” The Journal of Aviation Medicine 12 (Sept 1941):302.

J Cochrane. “Final Report on Women Pilot Program.” 38.

JR Betson and RR Secrest. “Prospective women astronauts selection program.” American Journal of Obstetrics and Gynecology 88 (1964): 421–423.

Kanas and Fedderson’s 1971 report went on to conclude: “Information regarding women during periods of stress is scanty. This lack, plus previously mentioned problems, will make it difficult for a woman to be a member of the first long-duration space missions. However, it is just as unlikely to think that women cannot adapt to space. Initial exploration parties are historically composed of men, for various cultural and social reasons. Once space exploration by men has been successfully accomplished, then women will follow. In preparation for this, more information should be compiled regarding the physiology and psychology of women under stressful situations.”

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Fortune magazine cover designed by Arthur Lidov, depicting Maxwell’s thermodynamic surface of an “imaginary substance” similar to (though not quite) water based on J. W. Gibbs’s work, alongside Gibbs’s formula for the phase rule, bottom left

To describe a closed, homogeneous system — that is one of constant composition, such as an ideal gas — we need two parameters of state (e.g. T and p). For a heterogeneous system in equilibrium, consisting of one component (e.g. water) and two phases (e.g. liquid and vapour), we require only one parameter of state (e.g. T).

This can be expressed with Gibbs’s phase rule, which specifically describes the number of possible degrees of freedom (or variance) of a chemical system (where C = number of components, P = number of phases in the system): F = C ‒ P + 2

The number 2 is specified because this formulation assumes both T and p can be varied.

The thermodynamic surface for a typical substance is shown in this diagram, with the x axis (width) indicating volume, y axis (height) indicating pressure and z axis (depth) indicating temperature.

Water is thermodynamically atypical, as is readily observed from icebergs that float on liquid water — this can be seen by comparing this diagram to the illustration above, after Maxwell’s 1874 sculpture (itself based on Gibbs’s papers). Maxwell used coordinates of volume (x), entropy (y) and energy (z) — plotted from surrogate measures of pressure and temperature.

Maxwell stated that this model allowed “the principal features of known substances [to] be represented on a convenient scale”.

The construction of this was far more interesting than that of any automatist dream painting (though here the cover art is clearly trying to conjure up the surrealist landscapes of Magritte and contemporaries)

The numerical data about entropy can only be obtained by integration from data which are for most bodies very insufficient, and besides it would require a very unwieldy model to get all the features, say of CO2, well represented, so I made no attempt at accuracy, but modelled a fictitious substance, in which the volume is greater when solid than when liquid; and in which, as in water, the saturated vapour becomes superheated by compression. When I had at last got a plaster cast I drew on it lines of equal pressure and temperature, so as to get a rough motion of their forms. This I did by placing the model in sunlight, and tracing the curve when the rays just grazed the surface…

A superb summary of the two scientists’ graphical methods was put together by Ron Kriz at Virginia Tech (view full size image here). The melée of multi-coloured lines is a bit perplexing, and bringing a physical sculpture in to demonstrate the concept — stepping away from the 2D triple point plots still used in undergraduate lectures today — was a stroke of genius in a time long before the advent of sophisticated computer visualisations.

This general graphic method was not just to plot existing thermodynamic data, but rather to envision total derivatives — related to the work on vector calculus Gibbs was renowned for (his lectures on the subject were collected at the start of the 20th century to form an influential textbook).

Dr Kriz feels this object should provoke reflection on how we consider visualisation methods in science:

The development of the thermodynamic theory of state is a rare but excellent example that demonstrates how scientists combine analytic and graphical methods together with how they understand science. How scientists combine analytical and graphical models into new knowledge exemplifies a cognitive processes that includes visual thinking or what Dr. Daniel Coy describes as “geometric reasoning”. This new knowledge was reported and documented by Gibbs as a graphical method, so that others could reproduce and build on that understanding. As the graphical method was being developed by Gibbs the intent was not to use graphics for presentation but rather to develop the theory. This is contrary to the popular belief that imaging in science is used for presentation which can at times be insightful.

After reading and studying Gibbs and Maxwell, perhaps the reader would agree that neither Gibbs nor Maxwell developed their graphical method for presentation, a metaphor, or as an intriguing anecdotal experience that could not be scientifically reproduced. Rather the graphical method was sufficiently developed and described by Gibbs to be inclusive with developing the thermodynamic theory of state, which was reproduced and further developed graphically by Maxwell. Recall in summary Gibbs states,

In the foregoing discussion, the equations which express the fundamental principles of thermodynamics in an analytical form have been assumed, and the aim has only been to show how the same relations may be expressed geometrically. It would, however, be easy, starting from the first and second laws of thermodynamics as usually enunciated, to arrive at the same results without the aid of analytical formulae, to arrive, for example, at the conception of energy, of entropy, of absolute temperature, in the construction of the diagram without the analytical definitions of these quantities, and to obtain the various properties of the diagram without the analytical expression of the thermodynamic properties which they involve.

This is not a subjective process, e.g. what visual tools were used, how were they used, or how were the tools designed. The integrity of Gibbs’ and Maxwell’s graphical method is a well established, scientific, objective, and a reproducible process that has nothing to do with the subjective use of tools. This graphical method is inclusive with the developement of the thermodynamic theory of state where Gibbs demonstrates that understanding this theory can be accomplished “...without the aid of analytic formulae”, e.g. his equation of state. In fact Gibbs thought his graphical method was so important that,

Such a course would have been better fitted to show the independence and sufficiency of a graphical method, but perhaps less suitable for an examination of the comparative advantages or disadvantages of different graphical methods.

Hopefully the independence and sufficiency of a graphical method, as proposed by Gibbs, was developed and demonstrated here by envisioning energy as a surface defined as a scalar function of two independent variables, e.g. entropy and volume, where the gradient of the scalar function are slopes tangent to this surface and equal to temperature and negative pressure, as defined in Figs. 5 and 8. However since neither this surface nor the gradient lines tangent to this surface are not associated with a specific set of physical properties, this general graphical method is indeed coextensive in its application.