Transcript Material Selection: Propellant Chamber

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
Motivation
•
•
•
•
•
Mechanical-based MEMS
High thrust-to-weight ratio
Guidance systems
Miniature satellites
Integrated sensing systems (Smart Dust)
Outline
•Microrocket Comparisons
–Turbine Engine
–Gaseous Propellant Rocket
–Solid Propellant Rocket
•Case Study: Solid Propellant Rocket
–Fabrication
–Materials Considerations
–Geometric Considerations
–Performance
•Conclusions
3 Major Categories of Micro-Rocket
• Turbine Engine
• Gaseous Propellant Rocket
• Solid Propellant Rocket
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
Micro Gas Turbine Engine
Gaseous Propellant Rocket
Characteristics
– 18 mm x 13.5 mm x 3 mm
– Thrust-to-Weight Ratio = 85:1
Advantages
– No Moving Parts
– Efficient and Powerful
Disadvantages
– External Fuel Supply Required
– Slow Fabrication Process
Gaseous Propellant Rocket
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
Solid Propellant Rocket
Case Study:
Solid Propellant Microrocket
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 microrocketapplication to micropropulsion”, Sensors and Actuators A, vol. 99, (2002) pgs. 125-133
propellant
chamber
convergent/
microheater
divergent
Microheater/Convergent
Highlights:
• Microheater
– Wet oxide growth
– LPCVD SiN1.2
– LPCVD Poly-Si for
resistor
– CVD gold electrical
pads
• Convergent
– KOH anisotropic etch
Poly-Si
Gold
SiN1.2
SiO2
Si
SiO2/SiN1.2 membrane
Microheater
Poly-Si resistor
Gold electrical
pad
Propellant Chamber
Si
Highlights:
• DRIE
– ASE (SF6, C4F8)
Divergent
Highlights:
• Oxide growth
• Anisotropic Etch
– 45wt% KOH
– 80°C
Si
Assembly of Parts:Propellant 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
Assembly of Parts: Epoxy Bonding
Highlights:
propellant
chamber
• Epoxy
– EPO TEK H70 glue
– cured at 60°C for 15
hours
convergent/
microheater
divergent
• Array Fabrication
Note
Rossi, C., et al., “Design, fabrication and modeling of solid propellant microrocket-application to micropropulsion”, Sensors and
Actuators A, vol. 99, (2002) pgs. 125-133
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
Material Considerations:
Propellant
• Heterogeneous solid propellant
– Polymeric binder (PB), metal catalyst (Al, Mg),
oxidizer (NH4ClO4)
– Relatively high energy density
– Stable and viscous
– Adaptable properties
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
Ac
– Burn time: 350ms
• Ac/At = 60 (chamber diam. = 0.85mm)
– Sonic under all conditions
– Thrust force: 4.8 – 5.8mN
– Burn time: 250ms
At
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
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