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What are the orders of magnitude of disturbing torques on the ISS itself, preferably split into the following categories, but any numbers (with source) will be useful:

  • Gravity gradient
  • Magnetic
  • Solar Radiation Pressure (SRP)
  • Thrust misalignment
  • Mass movement

Related:

Why doesn't the ISS start to spin if people walk inside?

How well and how rapidly can the ISS attitude control system detect periods of astronaut activity?

Michel Touw
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    You are missing what I believe is the largest torque outside gravity gradient - drag. Despite being at 400km, the ISS still encounters some atmosphere, which applies torque. I may be able to answer this question in more detail later, but probably not till tomorrow. – Arthur Dent May 11 '17 at 15:46
  • Without sources, I can say with decent confidence that your gravity gradient and drag torques will be the largest (they stabilize each other though), with your next largest being SRP. Thrust misalignment will be difficult to calculate, particularly because it will be very variable. Magnetic is very small, and mass movement again completely depends on what you're moving.

    What do you need to know this for? That will help a lot to answer this.

     – Arthur Dent May 11 '17 at 16:41
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    In addition to what @ArthurDent wrote (with which I totally concur), there are internal disturbances from the very large motors that turn the solar arrays and radiators, and occasionally, from moving the robotic arms. – David Hammen May 11 '17 at 16:44
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    I can produce an arbitrarily large torque with a fixed impulse of arbitrarily short duration, but it won't produce an arbitrarily large change in the motion of the station. It also makes a big difference whether you're interested in effects that would produce a secular trend in the angular velocity vector or only a transient change. Transient changes could, e.g., mess up microgravity experiments, but won't affect the station's ability to stay oriented toward the earth's surface. –  May 11 '17 at 19:57
  • @ArthurDent: I don't know if it's the largest torque. The force is around 0.275N and not much of it transfers into torque. – SF. May 12 '17 at 08:39
  • @SF. what would be larger? The drag torque and gravity gradient stabilize each other. So a larger torque would have to be more than either of those. I'm sure mass movement could be larger, but again that's variable. They're both surely larger than SRP and magnetic. – Arthur Dent May 12 '17 at 14:54
  • @ArthurDent: How is the drag torque oriented? Isn't it dependent on solar panels orientation and such, varying a lot over the orbital period? – SF. May 12 '17 at 14:56
  • @SF. The drag force always acts in the velocity direction. The solar panels move via alpha and beta angles, and don't actually affect the torque from drag (since there will always be symmetry). The only times the drag torque will be different is from 1.) A docked vehicle or some small components that aren't symmetric (like the arm) or 2.) the station is performing some sort of maneuver. The first point would be pretty minimal. Check out the answer to this question. – Arthur Dent May 12 '17 at 15:55
  • @ArthurDent: The panels, turning, may act as wings with lift. They all turn to the same angle (facing the Sun) arbitrary relative to station, so there's no symmetry there. – SF. May 12 '17 at 16:03
  • @SF. Lift is very different, and requires a continuum. And by symmetry, I mean there is the same amount of surface area facing the velocity direction on either side of the x-z plane. Even when turned, the torques will even out. Even if they don't, the torque about the z axis will be insignificant relative to the y-axis torque. – Arthur Dent May 12 '17 at 16:17
  • @ArthurDent: Lift and drag are tightly related, proportional to the same medium density and velocity, and through less straightforward relation to angle of attack. The panels pivot in the Z axis, and are about 4 meters forward from ISS CoM. If they are turned all the same 45 degrees left from the X axis (Sun ahead and left of ISS which is heading and moving southeast, over the morning terminator), the oncoming medium, besides (symmetric) backwards force (drag), will exert force pushing them right, exerting right (clockwise) torque on the station in the Z axis. – SF. May 12 '17 at 19:13
  • @SF. You're right about lift, I was confusing myself. While a continuum does provide the pressure difference, the momentum transfer of particles would still produce a force in the direction perpendicular to velocity. I'm still not sure about the torque, however. Just doing a simple FBD, even at a 45 degree angle, the same number of particles hit both sides of the solar panels. For now though, this discussion is already taking up a lot of space. Regardless of who's correct, I don't believe solar panel torque would compare with the torque about the y axis. – Arthur Dent May 12 '17 at 21:22

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