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The Zero G Propellant Measurement Problem

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The Zero G Propellant Measurement Problem Modal Propellant Gauging of Spacecraft Propellant Tanks using Piezoelectric Transducers Rudy Werlink MS PE (NASA/KSC) AST Fluids (NE-M5) Nehemiah Joel Williams, Ph.D. (NASA/JSC) AST, Liquid Propulsion Systems (EP-4) The zero g propellant measurement problem Long term use and transfer of propellants including cryogenic fluids in space is required for many deep space travel technologies but there are several unsolved problems including- Propellant gauging in Space (very low gravity) all current methods have large disadvantages. Further, the lack of robust low-gravity gauging methods generates significant added costs to satellite mission plans. Background for Modal Propellant Gauging • The idea to use active vibration responses to measure mass of a vessel especially in zero g came from a discussion about a another zero g experiment being planned at KSC NASA to study the flow of 2-phase liquids in space using several tanks. The NASA PZT active vibration modal system was already being developed to provide a health monitoring system on structures, composite tanks, etc. • NASA KSC put a request to the Flight Opportunities program with Carthage College in Kenosha, Wisconsin wining the proposal. The first experiment using the PZT modal system on the Zero g aircraft was in 2010. The results were very encouraging. MPG principal of operation Modal Analysis Modal analysis is a commonly used technique in the analysis of structures. Acoustic forces are applied to the structure and the vibrational response of the structure is recorded through sensors affixed to the surface of the structure. Natural vibrational modes of the structure are excited resulting in increased amplitude in sensor response at the excited mode frequencies. Resonant modes are calculated by means of a Frequency Response Function (FRF). The FRF is the ratio of the Fourier Transform of the response signal to the Fourier Transform of the input signal. The FRF produces peaks at the natural vibrational mode frequencies of the structure. Changing the volume of liquid in the tank lowers the resonant mode frequencies by increasing the effective mass. The essential signal chain is illustrated in schematic form in Fig. 1. The basic equation is: 퐾 Frequency = 푀 Where K is the material stiffness which is affected by the type, geometry, temperature of the material and external stress such as pressure, M is the modal mass of the system. NASA (Lead Zirconate Titanate )* PZT modal active vibration technology for non-invasive fluid mass measurement • Experiment concept. A PZT patch actuator is adhered to an experimental tank partially filled with water. Broadband white noise is introduced to the tank through the actuator. The Frequency Response Function is computed from the FFTs derived from the sensor and monitor signals. (PZT refers to the type of Piezoelectric sensor/actuator Pb[ZrxTi1-x]O3 , I also use the abbreviation loosely to Refer to the active vibration system) 4/5/2016 5 PZT sensor/actuator background The MFC consists of rectangular piezo ceramic rods sandwiched between layers of adhesive, MFC P1 type (d33 effect), Elongator electrodes and polyimide film. The electrodes are attached to the film in an interdigitated pattern which tranfers the applied voltage directly to and from the ribbon shaped The P1 type MFCs, including the F1 and S1 types are utilizing the d33 effect for actuation and rods. This assembly enables in-plane poling, actuation and sensing in a sealed and durable, ready will elongate up to 1800ppm if operated at the maximum voltage rate of -500V to +1500V. The P1 type MFCs are also very sensitive strain sensors. to use package. As a thin, surface conformable sheet it can be applied (normally bonded) to various types of structures or embedded in a composite structure. If voltage is applied it will MFC P2, P3 type (d31 effect), Contractor bend or distort materials, counteract vibrations or generate vibrations. If no voltage is applied it can work as a very sensitive strain gauge, sensing deformations, noise and vibrations. The MFC is also an excellent device to harvest energy from vibrations. The MFC is available in d33 and d31 operational mode, a unique feature of the Macro Fiber Composite. The P2, P3 type MFCs are utilizing the d31 effect for actuation and will contract up to 750ppm if operated at the maximum voltage rate of -60V to +360V. The P2 and P3 type MFCs are mostly used for energy harvesting and as strain sensors. Overview of Typical Properties: 28N to 1kN depending Max. blocking Force on width of MFC P,S,F1: -500 to +1500V Max. operating Voltage P2, P3: -60V to 360V Actuator: 10kHz Max. operating Frequency Sensor,Harvester:<3MHz Zero G plane flight experiments (Flight Opportunities Program) – Carthage College participant 2010-2016 Modal Propellant Gauging Data is based on a 20 second , 10-2g, the fluid is not stable (sloshing occurs), However with multiple averaged FRF data sets very good results are still obtained Actual FRF Peaks from previous 1 G data Zero G and one G Percent fluid volume vs. frequency 4/5/2016 8 Potential Launch opportunities for longer duration zero-G Experiments 1. Virgin Galactic return to flight : SpaceShipTwo is designed to offer 3-4 minutes of 10-3 to 10-5 g Payload experiment no larger than 18.50” W x 46.50” H x 21.50” D and less than 200 lbs. Use less than vehicle-provided power (24-28 V, ~50 W payload free of hazardous materials 2. LEO launch vehicles including Lockheed, Boeing, SpaceX, Blue Origin, ESA: to demonstrate MPG as a piggy-back technology for existing tank/fluid payloads Non-intrusive, low power (<50 watts), small size/weight <10 lbs. , 10 by 5 by 3 inches and reasonable data requirements - raw data can be processed to small FRF files and transmitted to Earth. 3. ISS and Orion Payload Space vehicle Requirements: In stable Zero G vary fluid volume by known amounts to establish MPG performance High interest in cryogenic fluids volume measurements in space : Suggest launching light weight LN2 filled composite tank with non-intrusive PZT sensors/actuator on sides and allowing liquid to change phase under zero-g. Venting to space thus allowing a single tank , simple design/controls and high quality data for nearly full-empty accurate calibration (by pre-determining the rate of change of fluid weight due to boiling) .
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