2. PURPOSE, OBJECTIVE, AND BACKGROUND OF WORK TO BE PERFORMED: CONTROL MOMENT GYROSCOPES (CMGS) ARE DEVICES…

Public award description

2. PURPOSE, OBJECTIVE, AND BACKGROUND OF WORK TO BE PERFORMED: CONTROL MOMENT GYROSCOPES (CMGS) ARE DEVICES FOR PRODUCING TRANSIENT REACTION TORQUES FOR VEHICLE CONTROL. AT ITS SIMPLEST, A CMG CONSISTS OF A SPINNING FLYWHEEL MOUNTED IN A FRAME, WHICH IS ITSELF FASTENED TO A FIX BASE VIA A PIVOT THAT PERMITS THE FRAME OR "GIMBAL" TO ROTATE ABOUT A FIXED AXIS THAT IS ORTHOGONAL TO THE FLYWHEEL'S SPIN AXIS. THE REACTION TORQUE IS PRODUCED BY ROTATING THE GIMBAL WHILE THE FLYWHEEL IS SPINNING, AND ITS MAGNITUDE IS THE PRODUCT OF THE THE FLYWHEEL MOMENT OF INERTIA, THE SPIN RATE OF THE FLYWHEEL, AND THE ROTATION RATE OF THE GIMBAL. CMG SYSTEMS THAT ARE INTENDED TO PRODUCE TORQUES IN THREE AXES FOR FREE-FLYING VEHICLES ARE FREQUENTLY BUILT UP FROM A SET OF FOUR GIMBALLED FLYWHEELS, ARRANGED SO THAT THE GIMBALS' FOUR ROTATION AXES REDUNDANTLY SPAN THREE DIMENSIONS. THE PURPOSE OF THIS TASK IS TO DEVELOP A PROTOTYPE CMG SUITABLE FOR CONTROLLING SMALL AERONAUTICAL VEHICLES FOR FLIGHT CONTROL RESEARCH, INCLUDING THRUST-LEVITATED VEHICLES CAPABLE OF VERTICAL TAKEOFF OR LANDING (VTOL) AND FIXED-WING AIRCRAFT. THERE ARE DECADES OF EXPERIENCE IN THE DESIGN AND APPLICATION OF CMGS FOR SPACECRAFT; HOWEVER, THE USE OF CMGS FOR CONTROLLING AERONAUTICAL VEHICLES IMPOSES A UNIQUE PERFORMANCE ISSUE UNADDRESSED IN THE SPACECRAFT-BASED STATE OF THE ART: THE VEHICLE HAS TO CONTINUOUSLY EXPEND ENERGY THROUGHOUT FLIGHT IN ORDER TO LIFT THE CMG AGAINST GRAVITY. THIS MAKES IT CRITICAL THAT THE CMG SYSTEM COMPRISE ONLY THE SMALLEST PRACTICAL FRACTION OF THE VEHICLE'S OVERALL MASS BUDGET. ALTHOUGH THE IDEAL AERONAUTICAL CMG WOULD BE CAPABLE OF SUPPLYING ANY DESIRED REACTION TORQUE TIME HISTORY WITH NEGLIGIBLE SYSTEM MASS, SUCH A SYSTEM WOULD BE VERY TECHNICALLY CHALLENGING. THE CMGS THAT ARISE FROM THIS EFFORT ARE TO BE USED IN SMALL, HIGH-RISK, FLIGHT EXPERIMENTS, THEY SHALL RELATIVELY INEXPENSIVE TO BUILD, RELYING ON COMMERCIAL OFF-THE-SHELF (COTS) COMPONENTS TO REDUCE COST. FINDING THE RIGHT DESIGN COMPROMISES BETWEEN PERFORMANCE AND COST IS CRITICAL IN THIS EFFORT, AND IT IS COMPLICATED BY THE FACT THAT THE BEHAVIOR OF THE CMG'S TORQUES IS CLOSELY COUPLED TO THE MOTION OF THE AIRFRAME ON WHICH IT OPERATES. BECAUSE OF THIS, THE CONTROL STRATEGY TO BE USED IN THE AIRFRAME/CMG SYSTEM IS, IN TURN, CLOSELY COUPLED TO THE CMG CHARACTERISTICS AND - IN TURN - CONTRIBUTES TO DEFINING THE CMG PERFORMANCE REQUIREMENTS. THE CONTROL ISSUES ARISING IN ATMOSPHERIC FLIGHT USING CMGS HAVE BEEN INVESTIGATED IN DETAIL OVER THE PAST SEVERAL YEARS IN THE DYNAMICAL SYSTEMS AND CONTROL BRANCH AT LANGLEY RESEARCH CENTER (LARC.)