Solid Propellant Micro-rockets: Application, Design and Fabrication

1
Solid Propellant Micro-rockets Application,
Design and Fabrication

• ME 381 Final Presentation
• 12/12/02
• Northwestern University
• Nik Hrabe
• Albert Hung
• Josh Mehling
• Arno Merkle

2
Motivation

• Mechanical-based MEMS
• High thrust-to-weight ratio
• Guidance systems
• Miniature satellites
• Integrated sensing systems (Smart Dust)

3
Outline

• Microrocket Comparisons
• Turbine Engine
• Gaseous Propellant Rocket
• Solid Propellant Rocket
• Case Study Solid Propellant Rocket
• Fabrication
• Materials Considerations
• Geometric Considerations
• Performance
• Conclusions

4
3 Major Categories of Micro-Rocket

• Turbine Engine
• Gaseous Propellant Rocket
• Solid Propellant Rocket

5
Micro Gas Turbine Engine

• Characteristics
• 2 cm x 2 cm x 4 mm
• Advantages
• Well Tested
• Disadvantages
• Moving parts
• External Fuel Supply Required
• Complicated Design and Fabrication
• Space Applications are Limited

6
Micro Gas Turbine Engine
7
Gaseous Propellant Rocket

• Characteristics
• 18 mm x 13.5 mm x 3 mm
• Thrust-to-Weight Ratio 851
• Advantages
• No Moving Parts
• Efficient and Powerful
• Disadvantages
• External Fuel Supply Required
• Slow Fabrication Process

8
Gaseous Propellant Rocket
9
Solid Propellant Rocket

• Characteristics
• 1 mm x 1 mm x 1 mm
• Energy Density 5 J/mm3
• Advantages
• No Moving Parts
• Self Contained Fuel Supply
• Preliminary Space Tested (STS-93, July 1999)
• Straightforward Fabrication Process
• Disadvantages
• 1 Time Use Only

10
Solid Propellant Rocket
11
Case Study Solid Propellant Microrocket
12
Fabrication

• Microheater/ Convergent
• Propellant Chamber
• Divergent
• Assembly of Parts
• propellant filling
• epoxy bonding of components

Rossi, C., et al., Design, fabrication and
modeling of solid propellant microrocket-applicati
on to micropropulsion, Sensors and Actuators A,
vol. 99, (2002) pgs. 125-133
13
Microheater/Convergent
Highlights

• Microheater
• Wet oxide growth
• LPCVD SiN1.2
• LPCVD Poly-Si for resistor
• CVD gold electrical pads
• Convergent
• KOH anisotropic etch

Microheater
14
Propellant Chamber
Highlights

• DRIE
• ASE (SF6, C4F8)

15
Divergent
Highlights

• Oxide growth
• Anisotropic Etch
• 45wt KOH
• 80C

Si
16
Assembly of PartsPropellant Filling
Highlights

• Localized Vacuum
• consideration of air pockets

Rossi, C., et al., Realization and performance
of thin SiO2/ SiNx membrane for microheater
applications, Sensors and Actuators A, vol. 64,
(1998) pgs 241-245
17
Assembly of Parts Epoxy Bonding
Highlights

• Epoxy
• EPO TEK H70 glue
• cured at 60C for 15 hours
• Array Fabrication Note

Rossi, C., et al., Design, fabrication and
modeling of solid propellant microrocket-applicati
on to micropropulsion, Sensors and Actuators A,
vol. 99, (2002) pgs. 125-133
18
Material Considerations Propellant Chamber

• Silicon
• Amenable to established microfabrication
  techniques
• High thermal conductivity (124W/mK)
• Ceramic (Macor)
• Low thermal conductivity (1.46W/mK)
• Adaptable to microfabrication

19
Material Considerations Propellant

• Heterogeneous solid propellant
• Polymeric binder (PB), metal catalyst (Al, Mg),
  oxidizer (NH4ClO4)
• Relatively high energy density
• Stable and viscous
• Adaptable properties

20
Modeling Geometric Parameters Chamber-to-Throat
Area Ratio

• Determines pressure in propellant chamber and
  flow speed at throat
• Maximize thrust when flow at throat is sonic
• Ac/At 16 (chamber diam. 1.0mm)
• Subsonic under atmospheric, sonic under vacuum
• Thrust force 1.5 5.0mN
• Burn time 350ms
• Ac/At 60 (chamber diam. 0.85mm)
• Sonic under all conditions
• Thrust force 4.8 5.8mN
• Burn time 250ms

Ac
At
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Modeling Geometric Parameters Divergent

• Guides expansion of exhaust gas from throat
• Unnecessary under atmospheric conditions (chamber
  pressure too low)
• Helpful under vacuum

Underexpanded
Optimal
Overexpanded
22
Conclusions

• Three microrocket designs
• Turbine Engine
• Gaseous Propellant Rocket
• Solid Propellant Rocket
• Significant advantages exist for the
  solid-propellant design
• energy density
• fabrication techniques
• lifetime