It takes huge amounts of deliberately applied energy to change their orbit. This is about the influence of the radiation on the sensors and systems which help to control the orientation of the satellites. In particular, magnetorquers use the magnetic field of the earth to (very slowly) dump excess angular momentum from the reaction wheels and control moment gyros.

Solar storms can also add a weak torque onto the satellite, depending on the orientation and shape of its body and solar panels. Again, the satellite has an attitude control system to handle such things, but it will still suffer the impulse response from the transient.

For the most part, orientation is measured optically or thermally - with sun sensors, earth sensors, and star trackers.