Attitude control compensator for flexible spacecraft

Claim 1

An attitude controller for a spacecraft having a body defining at least a primary self-resonant frequency, comprising: torquing means coupled to the spacecraft body for generating torques for changing the attitude of said spacecraft; sensing means coupled to said body for sensing the attitude thereof and for generating deviation signals indicative of the deviation of the attitude away from a desired attitude; PID control means for operating on attitude error signals for summing first, second and third products, said first product being formed by multiplying a first constant by said attitude error signals, said second product being formed by multiplying a second constant by the time derivative of said attitude error signals, and said third product being formed by multiplying a third constant by the time integral of said attitude error signals; coupling means coupled to said torquing means, said sensing means and said PID control means for coupling said PID control means in a control path responsive to said attitude error signals, and extending from said sensing means to said torquing means, for stabilizing said attitude, said coupling means further including compensation means cascaded with said PID control means, said compensation means having a transfer characteristic including a gain function which is substantially constant below a frequency of about ω/7, which gain function includes (a) a component representing a monotonic decrease in gain with increasing frequency from said frequency ω/7, superimposed upon (b) a notch component at a frequency of ω, where ω is selected to be slightly below the self-resonant frequency of said spacecraft, said transfer function including a phase response which tends toward zero degrees as frequency decreases from said frequency of ω/7, and which progressively lags toward -180 degrees with frequency increasing from ω/7 toward ω, and which from a value of +180 degrees at ω becomes monotonically more negative and tends toward -90 degrees at frequencies far above ω, whereby said compensation means cascaded with said PID control means responds to said deviation signals for driving said torquing means.