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Design and Testing of a Microthruster Test Platform for Accurate Thrust Measurement

This presentation explores the design and testing of a microthruster test platform capable of measuring thrust in the millinewton range. We address the challenges of measuring minute forces generated by microthrusters, emphasizing the importance of a rugged, modular design. Our solution employs two thrust measurement methods: direct using load cells and indirect using capacitive plates. The presentation details construction, sensor technology, signal processing, and testing procedures, aimed at improving accuracy and reducing noise in microthruster force measurements.

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Design and Testing of a Microthruster Test Platform for Accurate Thrust Measurement

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Presentation Transcript

  1. Erik Mueller Michael White Microthruster Test PlatformDesign Presentation II

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

  3. Microthrusters • Microthrusters produce <1N of thrust (mN range) • Various propulsion systems (standard, mono, 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

  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. Definition Direct vs. Indirect

  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 Induced Force Thruster

  16. Capacitive Pendulum • Uses electronic principle of capacitance • Needle point fulcrums eliminate frictional losses • Double pendulum plates eliminate mechanical noise

  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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