Post on 19-Dec-2015
MICROTHRUSTER TEST PLATFORM
DESIGN PRESENTATION
Erik Mueller
Michael White
Contents
•Introduction•Problem•Solution•Load-cell•Paddle-sensors•Testing•Q&A•Sources
Background
New type of small satellite Common subtypes are Cubesats and
nano-satellites Traditional thrusters designed to have
high power to weight ratio Minaturized thrusters replace
compressed gas attitude systems
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 plates Importance of two – better results,
redundancy
System Overview
System OverviewLoad Cell
Amplifier Circuit
DAQ NI USB-6008
Lab ViewSoftware
FM ModulatorCircuit
Fire Control
Indirect Thrust Plume Pendulum Sensor
Excel Data File
Excel Data File
DefinitionDirect vs. Indirect
Direct vs. Indirect
DirectMeasurement of the net forces acting on
thruster and any attached devices. Indirect
Measures only reactive forces from the thrust plume.
Sensing - Direct
Construction
Aluminum thruster bracket mounted directly to load cell
Mounting ChassisLoad 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
Mechanical Design
Sensing - Indirect
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
Capacitive Pendulum
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
Calculations
Given a distance of 1cm between plates C = A ε/d = 8.86pF A Frequency-Modulated system system
is sensitive enough at this range
Electrical Concept
Phase-locked loop is used to produce a discrete voltage signal, which is read by the DAQ.
Signal varies in amplitude, directly proportional to plate movement.
Phase Detector
Low-Pass Filter
VCO
fIN(t)
IN(t)
Error signal
ve(t)
Error voltage
vDC
fOUT(t)
OUT(t)Primary Oscillator
DAQ
Sensor
Schematic
Sensor Input
To PLL
Primary OscillatorPhase-Locked LoopFrom
Primary Oscillator
To signal processing
Signal Processing
To DAQ
Difference amp
From PLL
Software
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
Software
Software
Testing
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)
0 200 400 600 800 1000 1200-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
f(x) = 0.000983214285714287 x − 0.628952380952382
Calibration Test
Vout
Linear (Vout)
Grams, g
Vo
lts,
V
Testing
0 50 100 150 200 250 300 350 400 450 5002.017
2.067
2.117
2.167
2.217
2.267
2.317
2.367
2.417
2.467
2.517
f(x) = 0.000968723981900453 x + 2.01597586726998
Mass Calibration Test
Voltage, V
Linear (Voltage, V)
Mass, g
Vo
ltag
e, V
Testing
0.640000000000003 0.840000000000003 1.04-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
400 Hz Sample Frequency
Series1
Moving average (Series1)
Time, S
Vo
lts,
V
Testing – Rocket Test #2
Project Management
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
TimelineNov Dec Jan Feb Mar April May
Brainstorming X X
Research X X X X
Concept &Development
X X X
Sub-systemAssembly
X X X
Sub-systemTest
X X
Full systemTest
X X
Version 2.0 X
BudgetItem Cost($)
Estes rocket motors 50DAQ 150
Metal stock 40Strain gauges 40
Electronic components 100Paddle Sensors 100
Misc fund 50Total 530
Questions?
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