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Microthruster Test Platform Design Presentation II

Erik Mueller Michael White. Microthruster Test Platform Design Presentation II. Introduction Problem Solution Load-cell Paddle-sensors Testing Q&A Sources. Contents. Background. Microthrusters : Produce <1N of thrust ( mN range)

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Microthruster Test Platform Design Presentation II

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  1. Erik Mueller Michael White Microthruster Test PlatformDesign Presentation II

  2. Introduction • Problem • Solution • Load-cell • Paddle-sensors • Testing • Q&A • Sources Contents

  3. Background • Microthrusters: Produce <1N of thrust (mN range) • Various propulsion systems (fuel/oxidant, monopropellant, ion drive)

  4. The Problem • Thruster and forces involved are minute • Must be rugged and durable • Modular design preferable

  5. Our Solution • Two methods of thrust measurement • Direct – load cell • Indirect – capacitive plate • Importance of two – better results, redundancy

  6. System Overview

  7. System Overview Indirect Thrust Plume Pendulum Sensor FM Modulator Circuit Fire Control Load Cell Amplifier Circuit DAQ NI USB-6008 Lab View Software

  8. Direct vs. Indirect Definition

  9. 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.

  10. Sensing - Direct

  11. 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.

  12. Direct Force Measurement • Load Cell • Strain Gauge • Signal Amplification • Gain = 1000

  13. Mechanical Design

  14. Sensing - Indirect

  15. Indirect Thrust Measurement • Capacitive Plate System • Exhaust plume exerts force on a plate • Deflection corresponds to a change in capacitance Induced Force Thruster

  16. Capacitive Pendulum • Uses electronic principle of capacitance • Two plates, moving and reference • Needle point fulcrums mechanically isolate

  17. 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

  18. 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

  19. 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

  20. Software

  21. 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

  22. Software

  23. Software

  24. Testing

  25. 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.

  26. 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)

  27. Testing

  28. Testing

  29. Testing – Rocket Test #2

  30. Project Management

  31. 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

  32. Budget

  33. Questions?

  34. 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

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