Dynamic disturbance Sources o Reaction Wheel assemblies RWA Radial Force Disturbance PSD: B Wheel (xdirection) (RWAS are comprised typically of four wheels Applying torque to the wheels za0 creates equal and opposite torques on the spacecraft As a result, the wheels spin Static and dynamic imbalances in Wheel Speed(RPM) equency(Hz) wheels cause 6-DOF forces/torques to be imparted on the structure at the frequency of the wheel rPm Typically place on isolators and operate in frequency regions where structural response is low o System design requires careful Ithaco rWa,s trade between wheel balancing, Isolator corner frequency, vibration (www.ithaco.comp control etc roducts. html)Dynamic Disturbance Sources Dynamic Disturbance Sources  Reaction Wheel Ass emblies (RWAs) are comprised typically of four wheels — Applying torque to the wheels creates equal and opposite torques on the spacecraft — As a result, the wheels spin — Static and dynamic i mbalances in wheels cause 6-DOF forces/torques to be i mparted on the s tructure at the frequency of the wheel RPM. — Typically place on isolators and operate in frequency regions where structural response is low  System design requires careful trade between wheel balancing, isolator corner frequency, vibration control, etc. 0 50 100 150 500 1000 1500 2000 2500 3000 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 Frequency (Hz) RWA Radial Force Disturbance PSD: B Wheel (xdirection) Wheel Speed (RPM) PSD (N2 /Hz) Ithaco RWA’s (www.ithaco.com/p roducts.html)