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  • In what way does the rotating gyroscope help in changing the orientation of the international space station in space ?

  • Is there any other way to change the the orientation of ISS ?

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    $\begingroup$ With a ZPM. Not to be confused with Stargate Atlantis's zero-point modules (I can't help but wonder if some ISS engineer did that on purpose...). $\endgroup$ – David H Aug 2 '13 at 10:39
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    $\begingroup$ @user6972 more than answers your question. In principle, all it takes is a simple momentum wheel. Try sitting on a frictionless bar stool, holding a bicycle wheel horizontally (axle up) in front of you with one hand. With the other hand, set it spinning. While it spins, you will be turning the other way. When you then stop it from spinning, you will also stop turning, and you will be facing in a new direction. $\endgroup$ – Mike Dunlavey Aug 2 '13 at 19:14
  • $\begingroup$ @Hash Note that as written this is borderline on topic for this site (the physics of space maneuvers is on topic, but engineering implementation details are generally not). However, this is the perfect sort of question for the new Space Exploration site, so if you have future questions like this you may also want to consider asking there. $\endgroup$ – user10851 Aug 3 '13 at 16:58
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    $\begingroup$ how to migrate this question to space exploration can anyone guide me $\endgroup$ – Hash Aug 4 '13 at 9:27
  • $\begingroup$ First we decide if it's off topic here. If so, since you already posted it to Space Exploration, we'll just close it here. $\endgroup$ – David Z Aug 5 '13 at 20:44
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ZPM isn't the full answer. A combination of gyro and thrusters are used. Primarily they use Control Moment Gyroscopes (CMG) located in the Unity Module. Secondary options with more thrust are the Russian Control Thrusters on both Progress and Zvezda (means star) modules.

The CMG's are quite heavy gyroscopes at about 600 lbs each.

CM Gyroscope

Inside the black casing is a steel wheel that is about 220 lbs spinning at 6600 rpm, generating 3500 ft-lb-s of angular momentum. To move the wheels are adjusted to a specific position creating a torque on the ISS. And to keep the ISS stable the wheels can be adjusted to generate a torque that is equal and opposite of the torques being generated by atmospheric drag and gravity.

At least two CMGs are needed to provide attitude control and are the minimum necessary to steer and steady the station as it travels around the Earth every 90 minutes at a speed of more than five miles each second.

CMG

If the CMGs are working effectively then no fuel is used, because they are solar powered. There has been two failures. Because of that the ISS has reduced the maximum speed at which they rotate the gimbals. Making them more creative about how they do maneuvers and utilize the Russian attitude control thrusters more than had been initially planned which does consume fuel.

The torque model from each is a pyramid structure shown here:

torque

torque 2

The Russian Thrusters failed their first initial tests after sitting idle for 6 years, however they are now functional. They are shown circled in this image (with covers on):

Zvezda

Orbit boosts are routine before any ship docks with the station, although they're not always trouble-free. In Decemeber 2006 the thrusters on a Progress fired for 1,364 seconds to raise the station's orbit by five miles before space shuttle Discovery arrived. It was the second attempt—the first try was aborted after the Progress' engine computer malfunctioned after moving ISS just a single mile.

Aside from these regular orbit changes to meet incoming spacecraft, over the course of its life, the ISS will have to be moved several times to counter the effects of atmospheric drag on the huge solar panels.

Occasionally they also have to dodge junk too. Even with advanced warning, engineers wait until "the last minute" to fire thrusters to avoid a potential threat. The last minute means 1.5 orbits, or about 135 minutes, from the predicted point of collision. That gives the ISS two chances to move over or under any incoming danger. Waiting also allows the Space Control Squadron at Cheyenne Mountain in Colorado, which tracks debris in orbit, to refine its predictions about a possible collision. Changing orbits is very disruptive to the work done on the station and burns valuable fuel.

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