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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
2
Outline
• Introduction – MicroPyros project
• MicroPyros demonstrator– Millimeter-scale DEMO
• Microscale device– Design, fabrication, assembling– Characterisation
• Conclusion & outlook
3
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
4
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
5
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
6
Introduction
Solid
Monoliquid
Biliquid
Cold G
as
From B. Larangot, Conception, fabrication, caractérisation de matrices de micropropulseurspyrotechniques sur silicium, Thesis, LAAS/CNRS, 2004
2
7
Microthrusters : mm-scale DEMO
• Single shot microthruster Array of 4 x 4 microthrusters (16 thrusters)
Nozzles
Igniters
Chambers
Glass seal
8
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
9
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)
10
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)
12
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
3
13
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
17
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
4
19
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
21
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
25
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
26
SOI Igniters
27
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
28
Assembled SOI Thrusters
• One step filling procedure
• One bonding step (epoxy gluing)
• Heater: 200 to 400 ohms2 x 1 or 2 x 2 beams
29
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
30
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
6
31
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
32
MicroPyros
• Project funded by theEuropean Commission
• Involved partners: