I know the solar panels rotate independently, so theoretically there should be no need for keeping the station pointing prograde. It would also be problematic for docking maneuvers.

But on the other hand I've seen this impact risk heatmap image, which seems to suggest the station spends most of the time travelling in the direction of movement (otherwise the risk would be even across the ship).

So, is the ISS oriented prograde most of the time? And in case it does,

  • Are reaction wheels powerful enough/in a good position for that? Or are RCS thrusters used instead?
  • Wouldn't this continuous movement cause a lot of strain on the structural docking ports (the ones connecting the pressurized modules) over time?
  • Won't the entire station wobble a lot around its length?

1 Answer 1


"the station spends most of the time travelling in the direction of movement" Indeed.

Orientation wise, the ISS mostly flies in a "+XVV" attitude - it's positive X axis (the end with the US modules) is pointed into the velocity vector and its Z axis (the side with the cupola on it) points at the Earth .

This fine answer Does the ISS have a rotational motion in addition to its translational motion? contains good pictures of the situation showing which axis is which, and explains how the ISS rotates once per orbit, to keep in that attitude.

  • The ISS doesn't have reaction wheels, it has control moment gyros (CMGs).

Since the gimbals of the CMGs can constantly be in motion and are powered electrically, they can provide a constant, fine attitude control that counteracts the small aerodynamic and gravity gradient torques.

  • The torques produced by the CMGs are quite small.
  • That depends on what you mean by "a lot".

You might enjoy reading the source I used for the quote: The International Space Station - Operating an Outpost in the New Frontier especially Chapter 7, "Motion Control System - Navigator of the Heavens".

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    $\begingroup$ During some times during construction they kept the ISS in a sun facing attitude (always the same side pointing at the sun) to maximaise energy output of the solar panels... I'll have to search for a source for that... $\endgroup$
    – TrySCE2AUX
    Commented Aug 25, 2022 at 4:46
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    $\begingroup$ I believe +XVV is quite near the minimum-torque attitude in the current ISS configuration, but I don't know where I'd source that from $\endgroup$
    – Erin Anne
    Commented Aug 25, 2022 at 8:51
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    $\begingroup$ @TrySCE2AU they indeed flew other attitudes during assembly including quasi-inertial ones like XPH space.stackexchange.com/a/19732/6944 $\endgroup$ Commented Aug 25, 2022 at 11:31
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    $\begingroup$ @ErinAnne it's mentioned on page 124 of the reference I linked in the answer. "a typical torque equilibrium attitude ... as the space station coasts is YPR -4,-3,0." So yeah, only a few degrees different from the LVLH attitude typically flown. $\endgroup$ Commented Aug 25, 2022 at 12:00

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