design_final_e

design_final_e - EMFFORCE OPS MANUAL Space Systems Product...

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EMFFORCE OPS MANUAL Space Systems Product Development-Spring 2003 E Reaction Wheel Design (LW, WF) E.1 Role of RWA (LW) The spin-up process requires equating the centripetal force on a vehicle with the electromagnetic force generated by the magnets. This process is depicted in Figure E.1-A and in Figure E.1-B. Figure E.1-A shows the initial configuration of the dipoles. Although the finalized design of the system uses two large, coreless electromagnets, the electromagnets are represented here as effective dipoles. The dipoles begin perpendicular to each other. Figure E.1 -A: Initial Dipole Configuration Figure E.1-B depicts the two dipoles as they begin to spin up. As soon as a current is applied to the electromagnets, forces and moments are induced in the dipoles. The moments are due to the perpendicular geometry of the system at this point. These moments must be counteracted by applied torque from the RWA. The dipoles initially move in the directions of their respective net forces. As they begin to move, the applied torque from the RWA is decreased to induce centripetal motion of the system. As centripetal force increases, the applied torque continuously decreases, allowing the rotating dipoles to slowly align along the same axis. At the point where the dipoles are perfectly aligned and the centripetal force is equal to the total magnetic force, no more applied torque is necessary. At this point, the system is in steady-state rotation Figure E.1 -B shows the process of spin-up. Massachusetts Institute of Technology 1 Dept of Aeronautics and Astronautics
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EMFFORCE OPS MANUAL Space Systems Product Development-Spring 2003 Figure E.1 -B: Spin-up Configuration The RWA consists of a flywheel and a motor. The motor powers the flywheel and must provide the necessary torque to balance the moments that are produced by the electromagnets. The spinning wheel stores the system’s angular momentum, balancing the system and guiding the system through spin-up to steady-state rotation. The RWA functions on the principle of the conservation of angular momentum. Angular momentum is conserved because the spin-up maneuver is performed entirely using torques and forces that are internal to the system. Therefore, the sum of the angular momentum that accumulates in the wheels on the (in this case) two vehicles is equal and opposite to the angular momentum associated with the spinning of the system about its own center of mass. Massachusetts Institute of Technology 2 Dept of Aeronautics and Astronautics
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EMFFORCE OPS MANUAL Space Systems Product Development-Spring 2003 E.2 Requirements Wheel o As a minimum, the flywheel must store the angular momentum necessary to operate a two-vehicle system in a steady state maneuver. The vehicles will perform the maneuver at a separation distance (between vehicle centers) of two meters and a rotation rate of one rotation per minute. o
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This note was uploaded on 11/08/2011 for the course AERO 16.810 taught by Professor Olivierdeweck during the Winter '07 term at MIT.

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design_final_e - EMFFORCE OPS MANUAL Space Systems Product...

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