I wonder why the space agencies chose only 2 males for the Year In Space ISS Mission?

I think it would have made more sense to have at least 1 male and 1 female astronaut, or more preferably 3 male and 3 female astronauts, for the following 2 reasons:

  1. Compare any effects between males and females in long duration space missions;

  2. To have a minimal statistical comparison between differences in physiologies, 3 would be a minimum sample to establish any hint of any trends.

I am aware of a previous related question One year Mission: Using data from Valeri Polyakov? but I believe this to be a different question.

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    $\begingroup$ Sending fertile women into space is kind of cruel. $\endgroup$ Sep 15, 2015 at 15:36
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    $\begingroup$ Does seem rather a strange choice. The top ten longest space-flights were all done by men, and a woman has never been up for longer than a year (current record for a woman is 199 days) so it seems that to the extent that more data is needed about the effects on humans of prolonged flights, more new ground would be covered by sending woman as opposed to men. $\endgroup$
    – simplicio
    Sep 15, 2015 at 16:50
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    $\begingroup$ @OrganicMarble the Russians did it; but they did a horrible job of medical data collection/storage. Getting access to the data on long term space habitation that Roscosmos should have inherited from the Soviet program was a major priority of NASA when pushing for expanded collaboration following the fall of the Soviet Union. Unfortunately, when they finally did get a copy of the data, they discovered that it's quality was uselessly poor for what they wanted to do with it. $\endgroup$ Sep 15, 2015 at 18:37
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    $\begingroup$ @corsiKa - this is a medical research ethics and PR fallout question. Even if you find a willing female subject, how do you manage the bad repute you get after she a) becomes barren, b) gets cancer? There is Congress and their constituencies, after all, and you don't want any budget cuts. Please note that once you perfect rad protection from GCR/solar wind, you would want to send a woman aloft to demonstrate flight safety. $\endgroup$ Sep 16, 2015 at 5:07
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    $\begingroup$ @Zaibis - we know that one gets significant radiation dose in LEO, especially on a long mission (with SPEs and whatnot). Long stay in space increases the risk of cancer and infertility for women. Would you do this deliberately, and for what practical purpose? Please read carefully the second bullet from PearsonArtPhoto's answer below. $\endgroup$ Sep 16, 2015 at 9:05

2 Answers 2


The test had to start somewhere. There are a number of reasons why they couldn't simply do a 6 person stay, that make it somewhat difficult at least. These include:

  • There is a natural cycle to bring down astronauts from the ISS, in that a Soyuz needs to be replaced every 6 months. While in theory a crew could bring a Soyuz, and bring the old one down, that hasn't been done in some time.
  • NASA is required to follow OSHA standards, although they have a partial exemption for one particular aspect, namely that of radiation. My answer to this question gives the requirements, which are different for men and women. Women are more sensitive to radiation, because breast cancer is a bigger risk in women, and all other cancers are roughly equivalent between the two sexes. This means that the ideal candidate from NASA for a long duration test is an older male (But not too old).
  • There are a lot of astronauts who want to go up to space, but very few who currently have that opportunity. Reducing the opportunity to get to space makes astronauts unhappy.
  • Certain experiments that are running on the ISS require special training. There are more than just a long duration space flight test required. Thus, a new flow of astronauts is required.
  • There is one NASA and one Russian doing this test. That seems required to balance the ISS workload.
  • NASA chose a person with an identical twin, to give more exact comparisons.
  • No doubt there will be extra tests done on the two astronauts, which would take away from required astronaut duties, if not handled in limited doses.

Bottom line, they could have done this as you proposed, but they want to start slowly. This will give them valuable data, without causing risks. I'm sure if they learn anything interesting from this, they will continue doing similar tests.


They have several more years to do more of these experiments before they go to Mars.

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    $\begingroup$ An understatement if I ever saw one... $\endgroup$ Sep 15, 2015 at 16:10

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