Thrusters and Thrust Measurement

1. By: Michael White Thrusters and Thrust Measurement

2. Agenda • Definitions 3 Slides • Common Methodologies 7Slides • Capacitive Pendulum 4 Slides • Works Cited • Questions

3. What is Thrust? • Newton's Third Law • For every action there is an equal and opposite re-action. • Newton’s Second Law • Force = change in momentum with time

4. Thrust Con’t

5. Thrusters • Used for controlling orientation • Requires less thrust than propulsion system

6. Direct Force Measurement • Strain Gauge • Piezoelectric Sensor

7. Strain Gauge Force Measurement • Uses predictable elastic properties of materials • Change in resistance • Useful for measuring large forces • Commonly used in scales

8. Strain Gauge Thrust Measurement • Commonly used for more powerful propulsion systems • Difficult to isolate frictional losses and mechanical noise and vibrations

9. Piezoelectric Force Measurement • Material generates an electric potential when a force is applied • Shares the same pitfalls as strain gauge measurement

10. Position Measurement • Typically optical sensors are used • Uses the principles of Work and Energy

11. Position Measurement Con’t • Difficult to overcome mechanical noise and vibrations as well as frictional losses

12. Balance is Essiential

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

14. Noise Filtering Details • Needle point fulcrum • Reduced Contact Area = Reduced Friction • Double Pendulum • Identical pendulums react identically to stimulation

15. Calibration Details • Generate a mathematical model to define the forces acting on the pendulum • Simple Form • Fg = mg cosΘ • More advanced math required

16. Signal Processing • Series of amplifiers and filters used to measure the change in signal

17. Works Cited • http://www.grc.nasa.gov • http://images.machinedesign.com • www.answers.com/topic/piezoelectricity • 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 • A Double Pendulum Precision Thrust Measurement Balance, T.F. Yang, Ping Liu, F.R. Chang-Diaz, Harvey Lander, R.A. Childs, H.D. Becker and S.A. Fairfax, Plasma Fusion Center, Massachusetts Institute of Technology

18. Questions?