[frayesto]

I think what they are referring to is "angular momentum dumps". The reaction wheels have a fixed maximum amount of angular momentum. This is a function of the speed of the wheels themselves since the mass/moment of inertia is fixed.

Over time external forces continue to add momentum to the system (from drag/solar radiation pressure). In order to maintain a desired pointing direction this means the wheels must increase in velocity to "absorb" this momentum.

Eventually you need to "dump" the momentum using another external force, such as thrusters, or in this case the same solar radiation pressure.

Goal is to orient spacecraft such that external forces can be used to spin down the various reaction wheels, thereby "dumping" momentum out of the wheels.

This is pretty common on all spacecraft, but gets complicated/innovative when you have to do it in an emergency or if you don't have a full set of reaction wheels.

[jcims]

Just adding it because I think it's a cool use of the word. When reaction wheels are operating at maximum speed and can no longer exchange momentum with the spacecraft in both directions, they are considered 'saturated'.

[taneq]

'Saturated' is used in control systems engineering for any value (sensor input, drive output etc.) that has reached maximum or minimum value and can't be further increased/decreased. It's the same sense of the word as used in the HSV colour space in computer graphics.