Erik Mueller Michael White

Introduction Problem Solution Load-cell Paddle-sensors Testing Q&A Sources

 Microthrusters produce <1N of thrust (mN range)  Various propulsion systems (standard, mono, ion drive)

 Thruster and forces involved are minute  Must be rugged and durable  Modular design preferable

 Two methods of thrust measurement  Direct – load cell  Indirect – capacitive plate  Importance of two – better results

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

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.

 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.

 Load Cell  Strain Gauge  Signal Amplification  Gain = 1000

 Capacitive Plate System  Exhaust plume exerts force on a plate Induced Force Thruster

 Uses electronic principle of capacitance  Needle point fulcrums eliminate frictional losses  Double pendulum plates eliminate mechanical noise

 Given a distance of 2cm between plates  C = A ε/d = 4.43pF  A Frequency-Modulated system system is sensitive enough at this range

 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

 Using a PLL to detect deviations in frequency, which are then read by a DAQ Phase Detector Low-Pass Filter VCO f IN (t)  IN (t) Error signal v e (t) Error voltage v DC f OUT (t)  OUT (t)

 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

 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.

 y = 0.001x – (x = Force in grams)  x = (y /0.001) x 9.81 mN/g  x = y x 9810 (x = Force in newtons)

 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

ItemCost($) Estes motors120 DAQ150 Pipe clamps20 Metal stock500 Strain gauges80 Electronic components100 Paddle Sensors100 Misc fund50 Total1120

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 , 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