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Miniaturisation of Miniaturisation of SolidSolid PropellantPropellant ThrustersThrustersfor for SpaceSpace ApplicationApplication

D. Briand, P. Q. Pham, C. Rossi*, N. F. de RooijSensors, Actuators and Microsystems Laboratory (SAMLAB)

Institute of MicrotechnologyUniversity of Neuchâtel

Switzerland

*LAAS-CNRS, Toulouse, France

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Outline

• Introduction – MicroPyros project

• MicroPyros demonstrator– Millimeter-scale DEMO

• Microscale device– Design, fabrication, assembling– Characterisation

• Conclusion & outlook

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Introduction

• MicroPyros project objectives (2000-2003)

– Integration of energetic material, MEMS device and electronics to realise new performing PowerMEMS

– Application of Micropyrosystems to propulsion• Nanosatellite: micropropulsion for station keeping

• Solid propellant concept– Combustion of a solid material stored

in a micromachined chamber

nozzle

igniter

chamber

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Introduction

• Solid propellant technology

– Combustion : large quantity of energy from small volume

– Solid fuel : no leakage, stability in time

– No moving parts, eliminating frictional force and makingtechnological fabrication easier

– The chamber is not pressurised, the reservoir does not need to be massive

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Introduction

From B. Larangot, Conception, fabrication, caractérisation de matrices de micropropulseurspyrotechniques sur silicium, Thesis, LAAS/CNRS, 2004

Cold gasSolid propulsion

Thrust

Min

imum

Spe

cific

impu

lse

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Introduction

Solid

Monoliquid

Biliquid

Cold G

as

From B. Larangot, Conception, fabrication, caractérisation de matrices de micropropulseurspyrotechniques sur silicium, Thesis, LAAS/CNRS, 2004

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Microthrusters : mm-scale DEMO

• Single shot microthruster Array of 4 x 4 microthrusters (16 thrusters)

Nozzles

Igniters

Chambers

Glass seal

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Challenges

• Compromises between the reduction of the dimensionalfeatures and combustion process considerations

• Management in a very small volume of high temperatureand pressure that could lead to mechanical failure

• Limits of silicon and the introduction of best appropriatematerials implying to bond different materials together

• Compatibility of processing and assembling with the

propellant

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DEMO Design

– Array of 4 x 4 microthrusters– Chip size : 14.65 mm x 14.65 mm

Nozzle (IMT)

2 mm

~10°

1500 µm

500 µm

Ø 250, 500 µm

350 µm

1 mm

50 µm250 µm

Igniter (LAAS)

Chamber (IMT)

Seal (LAAS)

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DRIESiChamber(IMT)

RIE, DRIESi, polySi

Igniter(LAAS)

HF10%Foturan

Diverging angle : conic DRIECavity : KOH

SiNozzle(IMT)

TechnologyMaterial

DEMO Fabrication Technology

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DEMO Assembling

• Filling of the parts with propellant– Igniter– Sealed chamber

• Assembling– Anodic bonding– Thermal gluing (epoxy glue)

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DEMO: Tests• Set-up

– Source I, measure V(t) => power, energy calculated– Thrust balance : thrust force measurement (LAAS)

• Ignition tests (GAP / GAP)– Ignition power : 100–150 mW– Ignition time : 20–130 ms– Combustion time : ~ 320 ms

GAP

GAP

intermediatechamber

chamber

igniter

• Ignition tests (ZPP / GAP)

ZPP

GAP

intermediatechamber

chamber

igniter

– Ignition power 150–200 mW– Ignition time : 80–130 ms– Combustion time : ~ 270 ms

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DEMO: Thrust Force– Force without nozzle :

• ZPP : 1.2 mN• GAP : 0.28 mN

without nozzle

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with nozzle

– Force with nozzle (Ø500 µm)• ZPP : 13.5 mN• GAP : 2.3 mN

DEMO: Thrust Force

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Microscale Device

• Objective– Investigation of the limit of integration– Miniaturisation– Reduction of the number of parts

• Microthruster dimensions– MicroPyros DEMO (macro-scale device)

1500 µm x 1500 µm– Microscale device

1040 µm x 1040 µm and 500 µm x 500 µm(275 µm x 275 µm)

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Microscale Device Design

Nozzle

Igniter

Chamber

Seal

– Igniter on membrane(Design 1)

• Same design thanMicroPyros with smallerdimensions

– « Free standing » igniter(Design 2)• New design

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Igniters

• Heaters characteristics:

–3340 Ω720 x 720 µm2

1730 Ω1975 Ω390 x 390 µm2

830 Ω1020 Ω180 x 180 µm2

500 µm1 mmArea

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Nozzles

• Throat diameters

• Silicon bulk micromachining: DRIE and KOH

–X500 µm

XX375 µm

X–275 µm

500 µm1 mmDiameter

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Chamber Fabrication

• Technology developped for the mm scale design– DRIE of silicon wafers

– Wet etching of Foturan glass wafers

Si: 500 µm chambers50 µm grooves

Si: 500 µm chambers250 µm grooves

Foturan: 500 µm chambers

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Assembling

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Ignition and Combustion

–200-375 mW720 x 720 µm2

125-200 mW130-200 mW390 x 390 µm2

65 to 105 mW60-90 mW180 x 180 µm2

500 µm1 mmArea

• Constant current of 7.0 to 7.75 mA

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Ignition and Combustion

• Ignition time: 27 to 37 ms

• Ignition energy: 4.9 to 7.9 mJ

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Ignition and Combustion

-5

0

5

10

15

30 35 40 45 50 55 60

Time (ms)

Thru

st (m

N)

Chamber = 500 µm, Nozzle = 275 µm

-5

0

5

10

15

20

25

0 10 20 30Time (ms)

Thru

st (m

N)

Chamber = 1mm, Nozzle = 500 µm

-10-505

10152025

10 15 20 25 30 35 40 45 50

Time (ms)

Thru

st (m

N)

Chamber = 1mm, Nozzle = 500 µm

• Combustion time: 10 to 15 ms

• Thrust force: 12 to 23 mN

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Microscale Device: Compact design

– Array of 4 x 4 microthrusters, chip dimension of 8 x 8 mm2

Igniter - nozzle

Igniter

Chamber

Solidpropellant

275-500 µm

∆Φc500

µm

100 - 13050225

275175475

200

50

groove[µm]

180- 240

nozzle diameter[µm]

250

500

∆[µm]

Φc

[µm]

500

5

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SOI Igniters Fabrication• SOI igniters

Si suspended resistorsSi suspended resistors

- SOI- Si doping- Si DRIE- LPCVD Si3N4- conic DRIE- release : HF 50%- Al contacts

Nozzle

Without pn junctions

With pn junctions

nozzle

heaters

heaters nozzles

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SOI Igniters

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SOI Igniter Characterisation

– Maximum electrical power controlled by a limitation on the current delivered

0

20

40

60

80

100

0 2.5 5 7.5 10 12.5voltage [V]

curr

ent I

r [m

A]

0200400600800100012001400

pow

er [m

W]

I (V)

P (V)

400 µm

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Assembled SOI Thrusters

• One step filling procedure

• One bonding step (epoxy gluing)

• Heater: 200 to 400 ohms2 x 1 or 2 x 2 beams

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Ignition SOI Thrusters

• Ignition time: 6 to 24 ms• Ignition power: 225 to 400 mW• Ignition energy: 1.6 to 11.8 mJ

Constant Current of 10 to 24 mA / beam

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Conclusion

• Micrometer scale device– Design and specification of a micrometer scale device

– Processing development to fabricate smaller igniterswith integrated nozzles

– Successful ignition of ZPP stored in sub-mm cavities

– Key points:• reproducibility of the propellant filling

• Development of propellant, igniters, filling and assembling are strongly linked

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Outlook

– Complete the characterisation of the ignition and combustion in smaller dimensions

– Optimised designs and fabrication processes • Nozzles• Igniters• Assembling

Validation of the technology in a space mission

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MicroPyros

• Project funded by theEuropean Commission

• Involved partners: