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