Small Satellite Dynamics Test Bed (SSTD): RWA Isolation Concept Oscar S. Alvarez-Salazar 11/17/2014

Background Reaction Wheel Actuators (RWA) generate harmonic forces and moments resulting from static and dynamic imbalances These disturbances can severely limit the fine pointing capability of a cube-sat given their small inertia Isolation of the RWAs offers a well understood strategy for improving pointing stability of a cube-sat – About a factor of 10 or better rejection per axis per layer of isolation Sample RWA Disturbance Model vs. Wheel SpeedEffect of Isolation on transmissibility

Target Isolation Performance > 4% damping Desired Isolation Envelope Primary Flex Modes: 3<f o <10 Surge ~10*f o

Isolator Design Considered isolation for – BCT XACT, – BCT 100 mNMs wheel – BCT 15 mNms wheel Requirements: – degrees of freedom isolation – Volume constrained for isolators – 3 – 10Hz isolator bandwidth – Damping of 4 – 10% – Testable in 1 g Design: – Blade isolators with 3 leaf spring configuration – S shape, angle varies between 30 to 60 degrees – Springs made out of Beryllium Copper, shaped then cured into spring shape – Constraint layer damping using visco-elastic material

RWA RWA D1D1 L D RWA 1-unit-cube-sat 10cm X 10cm Notional Isolator Design: 3-Leaf Spring Configuration (Bottom View)

RWA 1-unit-cube-sat 10cm X 10cm Notional Isolator Design: 3-Leaf Spring Configuration (Side View)  h

Beryllium-Copper Leaf Spring with VEM constraint-Layer treatment

Isolator Status Sized leaf springs to evaluate performance over a range of designs – Width 0.5cm – 2cm – Thickness 0.4 mm – 1mm – Length 5cm – 10cm Spring material purchased. Aluminum tape with polyethylene treatment identified for damping material. In talks with vendor for samples of three different thickness.