Before a human crew goes to Mars' moon Phobos or to even lower mass asteroids, could a long stay at such an object be simulated gravitationally in the space station? I've heard that the ISS people don't like movements which disturb their microgravity experiments.

But (when they are finished with that :) ) could the ISS at least for a few months spin enough to simulate the tiny surface gravity of Phobos? 0.0057 m/² I think. Wouldn't it be interesting to learn how dust fall and how humans orient in such an environment? If stuff eventually sail downwards, and if people prefer to sleep horizontally, then maybe that says something about what such miniscule gravity does to us. And maybe it would be good even for the ISS to swing a bit.


1 Answer 1


First off, there are good reasons here for why they didn't design for artificial gravity on the ISS. Also, it's not that there are some experiments on the ISS that require microgravity; rather, that migrogravity is largely the point of doing experiments on the ISS since most other conditions can be practically replicated on Earth. That aside...

  1. The components of the ISS were designed with microgravity in mind, not a constant centripetal force. Any constant rotation would produce extra stress, possibly beyond designed limits, on things that stick out like the solar panel arrays. Also, all pumping of fluids, air, etc would suddenly have the resistance of pumping uphill when going inward radially relative to the axis of rotation (and any valves/fitting/pipes on the outer edges would have to deal with additional pressure). Power (solar panels) and heat management (which require pumping ammonia through radiators) are some of the things you really don't want to get damaged and neither of them were set up with spinning in mind.

    There was also a question a while back (here, thanks Organic Marble) about what components on the ISS would be affected by the presence of gravity. One of the responses pointed out how the Water Recovery System is highly optimized for microgravity and would be negatively affected by the presence of gravity (it would most likely still work but possibly at reduced efficiency with Phobos-equivalent gravity). That's just one (highly critical) component: pretty much everything else on the ISS is also designed and optimized for use without gravity.

  2. The farther you are from the center of rotation the more acceleration you feel. Because the ISS is largely linear you would have to rotate end over end so there would be differing gravity forces between the outside ends and the center of rotation. Where would you target the gravity of Phobos: at the very ends? How much time to astronauts spend at the ends of the station, and for that matter do you get the data you want if the astronauts are constantly moving between the target gravity and much less as they move around the station?

  3. Disregarding the force produced by spinning, nothing on-board the ISS is designed to cope with the spinning itself.

    • The solar arrays are rotated for maximum sunlight collection; with the station spinning the arrays would have to constantly rotate counter to that, producing additional wear on the motors.

    • The center of rotation is defined by the center of mass, and since the station wasn't designed to spin that's not an intentionally placed location. That means that you're unlikely to have a docking port that's at the center so docking either gets very complicated or you have to despin for docking and departure.

  • $\begingroup$ The Space station could spin in a way that keeps its solar array pointed the same way, if you think about it. And "Phobos spin" would be quite modest. I can't imagine that it breaks stuff. Just having the crew sleeping in a module (be it a docked soyuz) with that simulated very low gravity would be interesting as a precursor for a Phobos mission, I think. (But maybe you're right, the ISS is worthless for human spaceflight? I think you're right, let the shit BURN!) It has cost more than cancer research, and it hasn't even cured microgravity, which isn't exactly epidemic on Earth, so... $\endgroup$
    – LocalFluff
    Sep 4, 2015 at 2:00
  • $\begingroup$ @1337joe mentions some good reasons why it wouldn't work. Let me give you the overriding reason: the ISS and all its systems were designed and optimized specifically for the free fall environment. There is no way it would work if you tried to put it under a constant g loading. The GNC and attitude control systems alone would go into the computer equivalent of shrieking hysterics. Remember this is the vehicle that used to lose attitude control because of the vent force from the steam emanating from space suit backpacks. $\endgroup$ Sep 4, 2015 at 2:44
  • $\begingroup$ @1337joe: Would that be "heat management", or are you indeed referring to the toilet facilities? $\endgroup$
    – DJohnM
    Sep 4, 2015 at 5:56
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    $\begingroup$ I for one wouldn't want to be the one doing the calculations, let alone calling the shots, on an orbital reboost on a rotating station which wasn't designed with spinning in mind from the beginning. So even if you can dock with the station while it is spinning (already a very risky maneuver, to the point that rendezvous and docking isn't in the first place), you'd still want to de-spin before the orbital reboost. $\endgroup$
    – user
    Sep 4, 2015 at 8:00

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