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MCE Jon Thermal Protection - Coggle Diagram
MCE Jon Thermal Protection
Re-entry
Apollo
Epoxy-novalac resin reinforced with quartz firbres and phenolic microballoons
TPS: Avcoat applied in honeycomb matrix, bonded to stainless steel structures
Ablative TPS
Rejects heat through:
Energy absorption during polymer pyrolysis
Gas flow in boundary layer
Formation of char layer and re-radiation
Char erodes away
Space Shuttle :rocket:
Multiple types of TPS
RCC - reinforced carbon-carbon
HRSI - High tmeperature reusable insulation (coated silica tiles)
LRSI - Low temp reusable surface insulation (fibrous silica tiles, excellent TSR but weak)
AFRSI - Advanced flexible reusable surface insulation (flexible fibrous blanket used instead of LRSI)
FRSI - Coated nomex felt reusable surface insulation
Reusable TPS: No ablation, rejects heat via:
re-radiation from surface and internal storage during high heating conditions
re-radiation and convective cooling under post-flight conditions
Reusable TPS Tiles
Coating
- black-glazed coating of borosilicate, shead 95% of heat, 5% absorbed by tile interior
Composition
- 90% air, 10% silica fibres few mm thick, feels like plastic foam.
Glue
- silicon rubber glue, like mastic, bonds tile to felt pad and then onto orbiters skin
Advanced TPS
TUFROC
Lightweight
Dimensionally stable
High total hemispherical emittance
Low catalytic efficiency
Thermal response similar to shuttle fibrous insulation
Consists of:
ROCCI Carbonaceous Cap
Silicon-oxycarbide phase slows oxidation
HETC treatment near surface slows oxidation and keeps emissivity high
Coated with borosilicate reaction cured glass for oxidation resistance
AETB Silica insulating Base
Solved thermo-structural issues by adding boron oxide and alumino-borosilicate fibres which also improved mech strength
Increased temp capability to >1370C by adding alumina fibre
Rockets :rocket:
Rocket nozzle
De Laval Nozzle
Shaped like a bell
Combustion chamber behind pinched neck
Exhaust reaches highest possible velocity before exiting
Gasses choke at the neck and expand into second bell, causing acceleration beyond speed of sound
:red_cross:Throat increases in diameter during use due to ablation of hot gasses
Acceleration is maximised when flow is perfectly expanded (exit pressure exactly equals the ambient pressure)
Nozzle optimised for launch will be less efficient at high altitude
Can be cooled by circulationg cryogenic liquid fuel or oxidiser on board
Variety of materials e.g. Copper alloy/steel, Grapite/tungsten/aluminium, carbon/carbon composites, Niobium (Spenny but v good, used on SpaceX)
UHTCMCs
Fibre preforms
Stacked 2D
Needled 2.5D
Woven 3D :moneybag:
Infiltrate
With slurries
With melt
Processing
Sinter (HP or SPS to densify matrix)
Pyrolyse (convert polymer-based matrix)
CVI (Fill porosity with matrix)
Dry: Powder filtered into fibre
Wet:
Stacking, vacuum bagging and HP
Homogeneization, vacuum bagging and HP (chopped fibre incorporated into slurry)
Fibre Pull out - good as consume energy when pulling out
RMI
Reactive Melt Infiltration: preform reacts with injected matrix
PIP
Polymer Infiltration Pyrolysis: Infiltration of a low viscosity polymer into the reinforcing ceramic structure (e.g. fabric) followed by pyrolysis
CVI
Chemical Vapour Infiltration: material is infiltrated into fibrous preforms using reactive gases at high temp to form fiber-reinforced composites
:check: Net shape, wide range compositions, processing T<1000C, matrix is pure and fine grained, can deposit interfacial layers in-situ
:red_cross: Very slow, requires repeated maching of surface to re-open porosity
Radio-frequency-CVI
:check: best microstructure, low temp, changing gas can deposit fibre coatings or change matrix, dense
:red_cross: Still slow, ~10% porosity, unknown costs
Inverse temp = inside-out infiltration, reduction of premature pore closure, shorter processing times
Testing
Stagnation tests
Stagnation temp: value at stagnation temp, when fluid speed is zero and all kinetic energy is converted into internal energy in combination with local static enthalpy
Rocket propulsion tests
Hypervelocity Flight
Speed >mach 5
Thermo-ablative testing
Self heating
Electric current through a bar shaped sample
:check: Upper temp and heating rate only limited by sample resistance
:red_cross: Hottest temp in centre of bar, difficult to know heat flux, no gas flow
OAT & OPT
Sample is rotated into a flame
Can adjust flame/sample distance
Arc Jet Testing
Gasses heated and expanded by continuous electrical arc between two electrodes
:check: Most realistic test, large samples can be tested
:red_cross: Not cheap, relatively few
UHTC Powder
OAT Tested
Powder near max-temp sinters and protects carbon fibres, liquid HfO2 formed is viscous enough to survive high velocity
Partial wetting of C fibres, full wetting is best
Melt Viscosity testing to prove theory
Drop of liquid oscillated
