2009 IEEE Aerospace Conference “Spacecraft Jitter Prediction using 6-DOF Disturbance Measurements” Bryce Carpenter Oliver Martin Jason Hinkle Sierra Nevada Corporation Space Systems Group IEEE Aerospace Conference March 2009

2009 IEEE Aerospace Conference 2 Problem Statement Beijing-1 Launch Oct meter resolution, 24-kilometer swath agriculture, city planning, hydrology, 2008 Olympics, … Challenges Flexibility Lower Cost Rapid Development Increased Agility … Power availability Smaller aperture Decreased pointing stability … Demand for Small Satellites

2009 IEEE Aerospace Conference 3 Paper Contribution Presentation Overview 4. System-Level Jitter Prediction An analytical technique for system-level jitter characterization prior to system integration 3. Structural Response Analysis 2. Frequency Domain Analysis 1. Hexapod Reaction Balance

2009 IEEE Aerospace Conference 4 Historical Background 2005 – 2007 Distributed Sensing Experiment (DSE) Missile Defense Agency (MDA) February 2008 Trailblazer Operationally Responsive Space (ORS) August 2, 2008 Falcon 1, Flight 3 launches from Omelek Island in Kwajalein Atoll SpaceX

2009 IEEE Aerospace Conference 5 Hexapod Reaction Balance Measurement device for accurately recording a wide range of dynamic force and torque responses PropertyValue Torque resolution0.2 mN-m Force resolution2 mN Maximum static torque100 Nm Maximum static force1300 N Transducer bandwidth kHz Stiffness normal to interface plate200 N/μm Unloaded first resonance800 Hz Steel Flexures Force Transducers Kinematic Transformation

2009 IEEE Aerospace Conference 6 Previous Hexapod Uses

2009 IEEE Aerospace Conference 7 Frequency Domain Analysis Convert time-series to frequency domain using Discrete Fourier Transform:

2009 IEEE Aerospace Conference 8 +Y Torque Waterfall Plot

2009 IEEE Aerospace Conference 9 Power Spectral Density Convert DFT to PSD:

2009 IEEE Aerospace Conference 10 Structural Frequency Response Analysis Conduct frequency response analysis in NASTRAN to determine camera motion due to RW disturbance Comm Deck Avionics Deck Payload Bay 28,339 Nodes 33,895 Elements

2009 IEEE Aerospace Conference 11 System Jitter Prediction Reaction Wheel Disturbance Flexible Body Response Predicted Payload Jitter

2009 IEEE Aerospace Conference 12 Payload Jitter Results

2009 IEEE Aerospace Conference 13 Conclusion SNC has developed the Hexapod to accurately measure high frequency forces and torques Analysis of Hexapod data can be combined with a FEM frequency response analysis to determine system pointing stability

2009 IEEE Aerospace Conference 14 Acknowledgments This material is based upon work supported by the U.S. Army Space and Missile Defense Command under Contract No. HQ D-0002.”

2009 IEEE Aerospace Conference 15 Outline Problem Statement –Demand for smaller spacecraft –Lower inertia causes the spacecraft to be most suseptable to disturbances, jitter is a particular issue Paper contribution (presentation outline) –Characterizing system level jitter prior to system integration Empirically measure actuator induced disturbances Determine flexible-body modes Background History –DSE -> Trailblazer -> Launch -> Bottom of the Ocean –Analyses was conducted during DSE phase to determine the affect of reaction wheel jitter on the target tracking camera Hexapod Reaction Balance –Device developed to accurately record wide range of dynamic responses –Description (2 plates, 6 piezoceramic force transducers with steel flexures) and mapping between forces and force/moments Measures time-series forces at 10kHz –Performance characteristics –Original and previous program uses, as well as DSE RW Frequency Domain Analysis –DFT, PSD, Waterfall Plots (theory and waterfall plots) Structural Frequency Response Analysis –Determines the structural response of the payload camera given a sinusoidal input from the RWs –Frequency Response Analysis (similar to Normal Modes Analysis) conducted in NASTRAN –FEM Model contained 28,339 nodes System Jitter Prediction –Combine component disturbances with flexible-body response to determine system-level jitter –Flow chart Conclusion –Acknowledgments (Funding and personnel)