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THE MODAL PROPELLANT GAUGING EXPERIMENT SEEKS TO DEMONSTRATE THE INFUSION POTENTIAL OF A NON-INVASIVE INEXPENSIVE AND ROBUST METHOD FOR GAUGING BOTH SETTLED AND UNSETTLED PROPELLANT AT GAUGING RESOLUTIONS OF 1% FOR SETTLED PROPELLANTS AND 2-4% FOR UNSETTLED SLOSHING PROPELLANTS. THE PROPOSED WORK REPRESENTS A SIGNIFICANT EXPANSION OF THE PREVIOUSLY FUNDED PROGRAM OBJECTIVES TO ADDRESS IMMEDIATE NEEDS IN THE ORION/SLS EXPLORATION MISSION ARCHITECTURE. SPECIFICALLY WE ADDRESS TWO CENTRAL OBJECTIVES IN THE PROPOSED WORK. (1) WE INTEND TO DEMONSTRATE 1% ZERO-G GAUGING RESOLUTIONS OF BAFFLE-SETTLED REALISTIC PROPELLANT SIMULANT IN MODEL PROPELLANT TANKS WITH INTERNAL PROPELLANT MANAGEMENT STRUCTURES. (2) WE INTEND TO VERIFY A CENTRAL HYPOTHESIS OF THE MPG APPROACH WHICH IS THAT THE MASS-LOADING OF TANK WALLS (AND THEREFORE THE MODAL FREQUENCIES) IS UNIQUELY DETERMINED BY THE ADHERED LIQUID LAYER. IN ORDER TO MEET THE PROPOSED OBJECTIVES TWO DISTINCT EXPERIMENTS WILL BE CARRIED OUT. THE FIRST OBJECTIVE WILL BE ACCOMPLISHED USING THE MPG PARABOLIC FLIGHT RIG WITH BAFFLE-SETTLED PROPELLANT SIMULANT. WE LL USE ISOPROPYL ALCOHOL (IPA) TO BETTER REPRESENT THE BOND NUMBER AND OTHER LIQUID-STRUCTURE PARAMETERS OF CRYOGENIC PROPELLANTS IN REAL TANKS. THE EXISTING COMPOSITE OVERWRAPPED VESSEL (COPV) TANKS WILL BE OUTFITTED WITH PROPELLANT MANAGEMENT DEVICES AND RING BAFFLES TO ACCURATELY REPRODUCE THE INTERNAL STRUCTURES OF THE ORION PROPELLANT TANKS. THE BAFFLES WILL BE DESIGNED AND TESTED TO PRODUCE SETTLED LIQUIDS WITHIN SECONDS AFTER THE ONSET OF ZERO-G PORTION OF THE PARABOLIC FLIGHT TRAJECTORY. THE TEST PLAN FOR OBJECTIVE 1 IS TO ACQUIRE 24 DATA POINTS AT 1% FILL-FRACTION INTERVALS AT 5 DATA POINTS PER FILL LEVEL (4X PARABOLIC FLIGHTS). THE SECOND OBJECTIVE WILL BE ACCOMPLISHED BY ESTABLISHING A ZERO-G EQUILIBRIUM LIQUID SURFACE AT THREE DIFFERENT FILL FRACTIONS IN SIMPLIFIED MODEL TANKS. WE WILL CORRELATE THE MODAL FREQUENCY SPECTRUM AT EACH FILL FRACTION TO THE ADHERED LIQUID LAYER MASS USING CAMERAS TO VERIFY SURFACE EQUILIBRIUM AND TO MEASURE ADHERED LIQUID MASS FRACTION AND BY USING OUR STANDARD MODAL SENSORS AND COMPUTATIONAL HARDWARE TO MEASURE MODAL RESPONSE. WE HAVE CARRIED OUT COMPUTATIONAL FLUID DYNAMICS (CFD) CALCULATIONS TO DETERMINE THE TANK SIZE AND FILL FRACTION SUCH THAT AN EQUILIBRIUM SURFACE CAN BE OBTAINED WITHIN THE FIRST MINUTE OF THE 2.5 MINUTES OF ZERO-G AFFORDED BY THE BLUE ORIGIN NEW SHEPARD SUBORBITAL VEHICLE. THE REMAINING 1.5 MINUTES WILL BE USED TO ACQUIRE MODAL DATA OF THE THREE TANKS WITH SETTLED LIQUID SURFACES.THE TEST PLAN FOR OBJECTIVE 2 IS TO UTILIZE A DOUBLE-LOCKER PAYLOAD EXPERIMENT ON BLUE ORIGIN S NEW SHEPARD VEHICLE. WE PROPOSE A SINGLE FLIGHT WITH AN EXPERIMENT CONSISTING OF THREE 6-INCH DIAMETER MODEL TANKS AT THREE DIFFERENT FILL FRACTIONS FOR WHICH SETTLED SURFACES CAN BE ACHIEVED IN<1 MINUTE OF CLEAN 0-G. PROPELLANT IS THE PRIMARY LIFE-LIMITING RESOURCE ON SPACECRAFT. ACCURATE GAUGING OF PROPELLANT VOLUME IN A MICROGRAVITY ENVIRONMENT HAS BEEN IDENTIFIED BY THE NASA EXPLORATION SYSTEMS ARCHITECTURE STUDY (ESAS) FINAL REPORT AS AN AREA REQUIRING SIGNIFICANT FURTHER DEVELOPMENT. THE MICROGRAVITY ENVIRONMENT RENDERS DIRECT VOLUME MEASUREMENT USING TRADITIONAL BUOYANCY- AND LEVEL-BASED TECHNIQUES INEFFECTIVE. INSTEAD INDIRECT METHODS ARE CURRENTLY USED TO ESTABLISH PROPELLANT VOLUME. THESE METHODS INCUR CONSIDERABLE ADDITIONAL MASS AND EXPENSE TO MISSION ARCHITECTURES. ADDITIONALLY TRADITIONAL METHODS OF PROPELLANT GAUGING SUFFER FROM DECREASING ACCURACY AS THE TANK EMPTIES SO THAT MASS-GAUGING ACCURACY IS LOWEST AT THE END OF MISSION LIFE WHEN GAUGING ACCURACY IS MOST IMPORTANT. FINALLY PREVIOUS WORK ON MPG HAS ATTRACTED IMMEDIATE INFUSION INTEREST FROM ORION PROGRAM MANAGERS AND THEIR SUPPORT FOR THIS PROPOSAL HAS HELPED SHAPE THE DIRECTION OF THE TECHNOLOGY MATURATION PLAN FOR THIS PROJECT.

THE MODAL PROPELLANT GAUGING EXPERIMENT SEEKS TO DEMONSTRATE THE INFUSION POTENTIAL OF A NON-INVASIVE INEXPENSIVE AND ROBUST METHOD FOR GAUGING BOTH SETTLED AND UNSETTLED PROPELLANT AT GAUGING RESOLUTIONS OF 1% FOR SETTLED PROPELLANTS AND 2-4% FOR UNSETTLED SLOSHING PROPELLANTS. THE PROPOSED WORK REPRESENTS A SIGNIFICANT EXPANSION OF THE PREVIOUSLY FUNDED PROGRAM OBJECTIVES TO ADDRESS IMMEDIATE NEEDS IN THE ORION/SLS EXPLORATION MISSION ARCHITECTURE. SPECIFICALLY WE ADDRESS TWO CENTRAL OBJECTIVES IN THE PROPOSED WORK. (1) WE INTEND TO DEMONSTRATE 1% ZERO-G GAUGING RESOLUTIONS OF BAFFLE-SETTLED REALISTIC PROPELLANT SIMULANT IN MODEL PROPELLANT TANKS WITH INTERNAL PROPELLANT MANAGEMENT STRUCTURES. (2) WE INTEND TO VERIFY A CENTRAL HYPOTHESIS OF THE MPG APPROACH WHICH IS THAT THE MASS-LOADING OF TANK WALLS (AND THEREFORE THE MODAL FREQUENCIES) IS UNIQUELY DETERMINED BY THE ADHERED LIQUID LAYER. IN ORDER TO MEET THE PROPOSED OBJECTIVES TWO DISTINCT EXPERIMENTS WILL BE CARRIED OUT. THE FIRST OBJECTIVE WILL BE ACCOMPLISHED USING THE MPG PARABOLIC FLIGHT RIG WITH BAFFLE-SETTLED PROPELLANT SIMULANT. WE LL USE ISOPROPYL ALCOHOL (IPA) TO BETTER REPRESENT THE BOND NUMBER AND OTHER LIQUID-STRUCTURE PARAMETERS OF CRYOGENIC PROPELLANTS IN REAL TANKS. THE EXISTING COMPOSITE OVERWRAPPED VESSEL (COPV) TANKS WILL BE OUTFITTED WITH PROPELLANT MANAGEMENT DEVICES AND RING BAFFLES TO ACCURATELY REPRODUCE THE INTERNAL STRUCTURES OF THE ORION PROPELLANT TANKS. THE BAFFLES WILL BE DESIGNED AND TESTED TO PRODUCE SETTLED LIQUIDS WITHIN SECONDS AFTER THE ONSET OF ZERO-G PORTION OF THE PARABOLIC FLIGHT TRAJECTORY. THE TEST PLAN FOR OBJECTIVE 1 IS TO ACQUIRE 24 DATA POINTS AT 1% FILL-FRACTION INTERVALS AT 5 DATA POINTS PER FILL LEVEL (4X PARABOLIC FLIGHTS). THE SECOND OBJECTIVE WILL BE ACCOMPLISHED BY ESTABLISHING A ZERO-G EQUILIBRIUM LIQUID SURFACE AT THREE DIFFERENT FILL FRACTIONS IN SIMPLIFIED MODEL TANKS. WE WILL CORRELATE THE MODAL FREQUENCY SPECTRUM AT EACH FILL FRACTION TO THE ADHERED LIQUID LAYER MASS USING CAMERAS TO VERIFY SURFACE EQUILIBRIUM AND TO MEASURE ADHERED LIQUID MASS FRACTION AND BY USING OUR STANDARD MODAL SENSORS AND COMPUTATIONAL HARDWARE TO MEASURE MODAL RESPONSE. WE HAVE CARRIED OUT COMPUTATIONAL FLUID DYNAMICS (CFD) CALCULATIONS TO DETERMINE THE TANK SIZE AND FILL FRACTION SUCH THAT AN EQUILIBRIUM SURFACE CAN BE OBTAINED WITHIN THE FIRST MINUTE OF THE 2.5 MINUTES OF ZERO-G AFFORDED BY THE BLUE ORIGIN NEW SHEPARD SUBORBITAL VEHICLE. THE REMAINING 1.5 MINUTES WILL BE USED TO ACQUIRE MODAL DATA OF THE THREE TANKS WITH SETTLED LIQUID SURFACES.THE TEST PLAN FOR OBJECTIVE 2 IS TO UTILIZE A DOUBLE-LOCKER PAYLOAD EXPERIMENT ON BLUE ORIGIN S NEW SHEPARD VEHICLE. WE PROPOSE A SINGLE FLIGHT WITH AN EXPERIMENT CONSISTING OF THREE 6-INCH DIAMETER MODEL TANKS AT THREE DIFFERENT FILL FRACTIONS FOR WHICH SETTLED SURFACES CAN BE ACHIEVED IN<1 MINUTE OF CLEAN 0-G. PROPELLANT IS THE PRIMARY LIFE-LIMITING RESOURCE ON SPACECRAFT. ACCURATE GAUGING OF PROPELLANT VOLUME IN A MICROGRAVITY ENVIRONMENT HAS BEEN IDENTIFIED BY THE NASA EXPLORATION SYSTEMS ARCHITECTURE STUDY (ESAS) FINAL REPORT AS AN AREA REQUIRING SIGNIFICANT FURTHER DEVELOPMENT. THE MICROGRAVITY ENVIRONMENT RENDERS DIRECT VOLUME MEASUREMENT USING TRADITIONAL BUOYANCY- AND LEVEL-BASED TECHNIQUES INEFFECTIVE. INSTEAD INDIRECT METHODS ARE CURRENTLY USED TO ESTABLISH PROPELLANT VOLUME. THESE METHODS INCUR CONSIDERABLE ADDITIONAL MASS AND EXPENSE TO MISSION ARCHITECTURES. ADDITIONALLY TRADITIONAL METHODS OF PROPELLANT GAUGING SUFFER FROM DECREASING ACCURACY AS THE TANK EMPTIES SO THAT MASS-GAUGING ACCURACY IS LOWEST AT THE END OF MISSION LIFE WHEN GAUGING ACCURACY IS MOST IMPORTANT. FINALLY PREVIOUS WORK ON MPG HAS ATTRACTED IMMEDIATE INFUSION INTEREST FROM ORION PROGRAM MANAGERS AND THEIR SUPPORT FOR THIS PROPOSAL HAS HELPED SHAPE THE DIRECTION OF THE TECHNOLOGY MATURATION PLAN FOR THIS PROJECT.