Placement of Reaction Control System on a Spacecraft

[colinshark]

Suppose you have a reaction wheel or a control moment gyroscope on your spacecraft for attitude control. This would be a self contained unit, with 3-axis control. Either device utilizes the conservation of angular momentum, trading angular momentum between the unit and the spaceship frame as needed for attitude control.

http://en.wikipedia.org/wiki/Reaction_wheel
http://en.wikipedia.org/wiki/Control_moment_gyroscope

Does the placement of the reaction control unit matter? Should it be as close as possible to the spacecraft 's center of mass for the best effect?

 

[colinshark]

I just looked at diagrams of the ISS, which uses a control moment gyroscope system.

The module is located in the "Z1 Truss", which is mounted rather closely to the station's center of mass.

Article about the Z1 Truss
http://iss.jaxa.jp/iss/3a/mis_z1truss_e.html

Diagram showing the placement of the Z1 Truss
http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm

Could the module be mounted on one of the outer ends and still perform well?

 

[Drakkith]

I think that placing it on the ends would introduce too much stress in the truss. You would be trying to move the entire mass of the station using only the truss.

 

[Mordred]

I agree this would have to be placed near center mass, this would be a point where it would be easiest to have an even spread of balanced forces in as many directions as possible. To place near an end would require more force applied on one side than the other.