design_final_a

design_final_a - EMFFORCE DESIGN APPENDIX Space Systems...

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EMFFORCE DESIGN APPENDIX Space Systems Product Development VOLUME II: DESIGN APPENDIX PROJECT: EMFFORCE Spring 2003 Space Systems Product Development Professor David Miller Massachusetts Institute of Technology 1 Dept of Aeronautics and Astronautics
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EMFFORCE DESIGN APPENDIX Space Systems Product Development A Control Algorithm Development (LS/AB) A.1 Control Requirements (LS) Electromagnets and reaction wheels are used to provide the forces and torques necessary to control position and attitude of the vehicles. The interaction between electromagnets of different vehicles can be controlled to either attract or repel the vehicles. The reaction wheels can rotate either clockwise or counterclockwise, providing control to either accelerate or decelerate the vehicles rotationally. Varying the current through the magnets and changing the speed of the wheels control the actuators. Controlling these accurately allows for maneuvering the vehicles and disturbance rejection. The responsibility of the control team was to build a robust controller for the project that will command maneuvers and provide disturbance rejection. The controller is located on the avionics computer, and processes metrology inputs in order to calculate the necessary commands to send to the actuators. This is depicted in the block diagram in Figure A.1-A . Figure A.1-A: Block Diagram of Controller The control team designed controllers to meet the following requirements, derived from the requirements document. 1. Exhibit control in two modes a. Spin-up/spin-down b. Steady state 2. Build a robust controller for two types of maneuvering a. Trajectory following b. Disturbance rejection 3. Maximum allowable error in separation distance is 15 centimeters for a separation distance of 2 meters between vehicles + _ Controller Preprogrammed Trajectory Plant Σ Sensors Actual Trajectory Metrology Algorithm Actuators Massachusetts Institute of Technology 2 Dept of Aeronautics and Astronautics
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EMFFORCE DESIGN APPENDIX Space Systems Product Development 4. Maximum allowable error in angular position is 5 degrees for each vehicle’s orientation 5. Rotation rate in steady state must be one revolution per minute The first requirement specifies the modes in which the test-bed operates. This is derived from the test case in which two vehicles are at rest, spin-up to steady state, and then spin- down to rest. Spin-up consists of controlling two vehicles initially at rest and positioned so that the electromagnet of the first vehicle is perpendicular to that of the second, as shown in Figure A.1-B. When the electromagnets are turned on, the vehicles rotate and shear in the directions of the arrows. By controlling the electromagnets and reaction wheels, thereby applying appropriate forces and torques on the vehicles, the vehicles will follow the trajectory specified in Figure A.2-C, where the arrows point to the “north pole” of the magnets.
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design_final_a - EMFFORCE DESIGN APPENDIX Space Systems...

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