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Explore a comprehensive presentation on designing an advanced microthruster test platform, covering methods for accurate thrust measurement, system overview, direct vs. indirect sensing, mechanical design, signal processing, and software integration. Gain insights into testing procedures, transfer function calculations, and project management strategies for efficient development. References sources from renowned institutions and researchers included.
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Erik Mueller Michael White Microthruster Test PlatformDesign Presentation II
Introduction • Problem • Solution • Load-cell • Paddle-sensors • Testing • Q&A • Sources Contents
Background • Microthrusters: Produce <1N of thrust (mN range) • Various propulsion systems (fuel/oxidant, monopropellant, ion drive)
The Problem • Thruster and forces involved are minute • Must be rugged and durable • Modular design preferable
Our Solution • Two methods of thrust measurement • Direct – load cell • Indirect – capacitive plate • Importance of two – better results, redundancy
System Overview Indirect Thrust Plume Pendulum Sensor FM Modulator Circuit Fire Control Load Cell Amplifier Circuit DAQ NI USB-6008 Lab View Software
Direct vs. Indirect Definition
Direct vs. Indirect • Direct • Measurement of the net forces acting on thruster and any attached devices. • Indirect • Measures only reactive forces from the thrust plume.
Construction • Aluminum thruster bracket mounted directly to load cell • Mounting Chassis • Load cell will be mounted directly to an aluminum chassis to provide a stable platform free of mechanical vibration • Load cell mounted vertically to reduce the effect of gravity on the test.
Direct Force Measurement • Load Cell • Strain Gauge • Signal Amplification • Gain = 1000
Indirect Thrust Measurement • Capacitive Plate System • Exhaust plume exerts force on a plate • Deflection corresponds to a change in capacitance Induced Force Thruster
Capacitive Pendulum • Uses electronic principle of capacitance • Two plates, moving and reference • Needle point fulcrums mechanically isolate
Calculations • Given a distance of 2cm between plates • C = A ε/d = 4.43pF • A Frequency-Modulated system system is sensitive enough at this range
Signal Processing • Using an FM generator, plates are a capacitor • Compare frequency shifts to determine deflection. • Advantage – more resistant to noise and distortion, very accurate • Disadvantage –more complex
fIN(t) IN(t) Low-Pass Filter Phase Detector VCO Circuit concept • Using a PLL to detect deviations in frequency, which are then read by a DAQ fOUT(t) Error signal Error voltage OUT(t) ve(t) vDC
Software • The NI USB-6008 DAQ will tie into a computer, along with the rocket ignition circuitry. • Both subsystems will be integrated into a single user-controlled program, using Labview
Testing • One rocket test has been performed to gauge ignition methods & rocket plume. • A calibration test was performed to verify strain subsystem linearity and determine transfer function. • A subsequent test was performed evaluate the strain subsystem. • Currently testing and revising software with the strain subsystem.
Transfer Function Calculation • y = 0.001x – 0.629 (x = Force in grams) • x = (y + 0.629/0.001) x 9.81 mN/g • x = y + 0.629 x 9810 (x = Force in newtons)
Work Breakdown Structure • Week 5-6 Subsystem and structure prototype • Week 6-7 Electrical circuit schematics • Week 5-9 Software composition and test • Week 7-10 Revision, second subsystem test • Week 9-12 Assembly, testing, revisions if needed • More details on website
Works Cited • http://www.grc.nasa.gov • http://images.machinedesign.com • www.answers.com/topic/piezoelectricity • http://www.boeing.com/defense-space/space/bss/factsheets/xips/xips.html • Traceable calibration of the 3-axis thrust vector in the millinewton range, EB Hughes and S Oldfield, National Physical Laboratory • Direct Thrust Measurement of In-FEEP Clusters, IEPC-2005-235, K. Marhold and M. Tajmar, ARC Seibersdorf research GmbH • Rocket Thrust Measurement For an Estes B6-2 Model Rocket Engine, Peter Hyatt, Jeremy LeFevre, Russell Dibb, Bringham Young University • Thrust stand for ground tests of solid propellant microthrusters, S. Orieux and C. Rossi and D. Esteve, Review of Scientific Instruments, Volume73, Number 7, July 2002 • A Ground Test Rocket Thrust Measurement System, Mary Fran Desrochers, Gary W. Olsen, M. K. Hudson, Department of Applied Science and the Graduate Institute of Technology, University of Arkansas • MilliNewton Thrust Stand Calibration Using Electrostatic Fins, Allen H. Yan, Bradley C. Appel, Jacob G. Gedrimas, Purdue University