Orbiter Passive Thermal Protection System

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Orbiter Passive Thermal Protection System
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Passive Thermal Protection System

• The Orbiter's passive Thermal Protection System
  (TPS) that covers nearly all of its surface
  consists of seven types of insulation
• The TPS insulation applied depends on the highest
  temperatures on a surface, the aerodynamic load
  and impact resistance at that region, and the
  density of the material
• For other applications such as movable joints and
  tile gaps, other protective methods are used that
  include thermal barriers and gap fillers

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Orbiter Passive Thermal Protection System

• Orbiter TPS original design requirements
• Limit aluminum alloy structure to a maximum
  temperature of 350 F
• 100 mission capability with cost-effective
  unscheduled maintenance/replacement
• Withstand surface temperatures from -250 to
  2,800 F
• Maintain the moldlines for aero and aero-thermo
  requirements
• Attach easily to aluminum structure
• Economical weight and cost

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Orbiter TPS

• Orbiter passive thermal tile types
• Reinforced Carbon-Carbon (RCC) - Used on the nose
  cap and wing leading edges where reentry
  temperatures exceed 1,260 C (2,300 F)
• High-temperature Reusable Surface Insulation
  (HRSI) - Used primarily on the Orbiter belly
  where reentry temperatures are below 1,260 C
• Toughened Unipiece Fibrous Insulation (TUFI) - A
  stronger, more durable tile that is replacing
  high and low temperature tiles in high-abrasion
  areas
• Low-temperature Reusable Surface Insulation
  (LRSI) - Originally used on the upper fuselage,
  but now mostly replaced by AFRSI
• Advanced Flexible Reusable Surface Insulation
  (AFRSI) - Quilted, flexible surface insulation
  blankets used where reentry temperatures are
  below 649 C (1,200 F)
• Fibrous Refractory Composite Insulation (FRCI) -
  FRCI tiles that have replaced some of the HRSI 22
  lb tiles provide improved strength, durability,
  resistance to coating cracking
• Felt reusable surface insulation (FRSI) - Nomex
  felt blankets that are used on the upper regions
  of the Orbiter where temperatures are below 371
  C (700 F).

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TPS Surfaces
Lower Surface
Upper Surface
TPS Legend
HRSI (Black) Tiles LRSI (White) Tiles AFRSI
Blankets
Side View
FRSI RCC
Glass Exposed Metallic Surfaces
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Leading Edge Structural Subsystem (LESS)
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Leading Edge Structural Subsystem (LESS)
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Leading Edge Structural Subsystem (LESS)

• Orbiter LESS consists of various reinforced
  carbon/carbon (RCC) parts
• Nose cap, 3 expansion seals, and 5 tee seals
• 44 wing leading edge panel/seal sets
• Chine panel located between the nose landing gear
  door and the nose cap
• Forward external tank attachment plates

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Leading Edge Structural Subsystem (LESS)

• LESS also consists of metallic attachments,
  internal insulation, and interface reusable
  surface insulation (RSI) tiles
• Basic design goals and purposes for the LESS are
  to provide thermo-structural capabilities for
  regions of the orbiter that exceed 2,300 F

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Reinforced Carbon-Carbon (RCC)
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TPS Reinforced Carbon Carbon

• RCC material functions
• SiC coating
• Oxidation resistance prevents oxygen flow in to
  substrate
• Graphite fibers
• Provide high strength at high temperature
• Thermal stability
• Carbon binder
• Provides rigidization
• High strength at high temperature
• Thermal stability
• Low porosity

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TPS - RCC

• Coating
• Substrate
• Coating

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TPS - RCC

• RCC panels and T-seal

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TPS - RCC

• Reinforced carbon-carbon material is fabricated
  in a number of steps that begins with the
  production of the carbon-carbon substrate
• Graphite-impregnated rayon cloth and phenolic
  resin are heat-cured in a vacuum
• A second application is made of alcohol furfural,
  then heat-treated in a vacuum to produce a shaped
  section of the carbonized composite substrate

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TPS - RCC

• The alcohol furfural is converted to a carbon
  layer and repeated two more time with vacuum
  heating
• The RCC substrate surface is coated with a
  mixture of aluminum, silicon, and silicon carbide
  then heat-treated with argon gas in several
  temperature cycle to prevent oxidation of the
  substrate which would shorten its lifetime
• The outer layer of silicon carbide is
  heat-treated with tetraethyl orthosilicate to
  eliminate thermal expansion difference with the
  RCC substrate

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Leading Edge RCC
A
Fixed Upstream Gap Between Panel and Tee Seal
A
E
E
HRSI Tiles
Section A-A
Variable Downstream Gap Between Panel and Tee
Seal For Thermal Expansion Allowance
B
Upper Wing
B
Detail D
Section B-B
Interface Gap Between RCC and HRSI Tiles
Upper LESS Access Panel HRSI Tiles
Upper Wing AFRSI
D
RCC Tee Seal Web (In Background)
Thermal Barrier
Section C-C
I nconel Attachments
C
ACSS Hardware
C
I nconel Insulators
Wing Spar
Upper Left Wing
RCC Panel (In Foreground)
Lower Wing HRSI Tile
Horsecollar Peripheral Gap Filler
Frank Jones NASA, KSC
Lower LESS Access Panel HRSI Tile
Section E-E
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TPS LESS RCC Flight Damage

• Pinhole formation
• Sealant loss
• Convective mass loss
• Micrometeoroid / orbital debris impact damage

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RCC Repair/Replacement
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Bonded TPS
HRSI tiles on the Orbiter 19,700
(9 lb), 525 (22 lb) TUFI tiles on the Orbiter
306 (8 lb) FRCI tiles on the
Orbiter 2,950 (12 lb) LRSI tiles
on the Orbiter 725 (9 lb), 77 (12
lb) FIB blanket area on the Orbiter
2,123 sq ft FRSI sheet area on the Orbiter
2,024 sq ft
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High-temperature Reusable Surface Insulation
(HRSI)
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TPS - HRSI

• High-temperature Reusable Surface Insulation
  tiles are used to insulate the Orbiter's
  underside aluminum alloy structure from the
  reentry heat that ranges from -157oC to 1,260 C
  (-250oF to 2,300 F)
• Like the other rigid Orbiter insulation tiles,
  the HRSI tiles are designed withstand
• On-orbit cold soaking
• Repeated thermal shock from heating and cooling
• Extreme acoustic environment during launch and
  reentry which can reach 165 decibels

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Tile Configuration
HRSI Tiles - Black RCG Coating
Gap
LRSI Tile White Glass Coating
Step
Densified IML Surface
Koropon-Primed Structure
Silicone RTV Adhesive
SIP
Uncoated Tile
Filler Bar
Coating Terminator
Frank Jones NASA, KSC
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Tile Configuration
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TPS - HRSI

• HRSI tiles range in thickness from about one inch
  to five inches
• HRSI tile thickness generally decreases rearward
  on the Orbiter since reentry thermal loads
  decrease rearward
• Each of the HRSI tiles has unique dimension
  specifications
• Must be machined individually
• Fitted by hand
• Typical replacement time for each of the HRSI
  tiles is about two weeks

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Wing Tiles Discovery (STS-114)
HRSI Tiles - Black RCG Coating
Gap
LRSI Tile White Glass Coating
Step
Densified IML Surface
Koropon-Primed Structure
Silicone RTV Adhesive
SIP
Uncoated Tile
Filler Bar
Coating Terminator
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TPS - HRSI

• HRSI Notes
• Surface coating on hard tiles including HRSI is
  reaction-cured glass (RCG)
• Sometimes referred to as RCG tiles
• Two different densities of HRSI tiles are used on
  the Orbiter
• HRSI tile density is based on heat loads - higher
  heat loads require higher density insulation tile
• 22 lb/ft3 is used for higher temperature regions
  around the nose and main landing gears, nose cap
  interface, wing leading edge, RCC/HRSI interface,
  External Tank/Orbiter umbilical doors, vent doors
  and vertical stabilizer leading edge
• 9 lb/ft3  is used on the remaining areas

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TPS - HRSI

• Each tile and blanket (but not RCC panels) is
  treated with a silicate waterproofing before each
  flight
• HRSI tile count on each Orbiter (as of 2002)
• 9 lb 19,700
• 22 lb 525

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Toughened Unipiece Fibrous Insulation (TUFI)
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TPS - Toughened Unipiece Fibrous Insulation
(TUFI) Tiles

• A newer tile called the Toughened Unipiece
  Fibrous Insulation is composed of the same silica
  fiber on the interior, but with a more durable
  surface coating
• These TUFI tiles are replacing some of the HRSI
  in regions requiring greater durability

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Low-temperature Reusable Surface Insulation
(LRSI)
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TPS - Low-temperature Reusable Surface Insulation

• LRSI tiles are of the same construction and have
  the same basic functions as the 99.8-percent-pure
  silica HRSI tiles
• Placed in areas that are exposed to lower
  temperatures and loads
• LRSI tiles are also thinner - 0.2 to 1.4 inches
• Typically made in 8 x 8 squares
• Like the HRSI tiles, thickness requirements for
  the LRSI are determined by the maximum
  temperature and heat load during reentry

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Advanced Flexible Reusable Surface Insulation
(AFRSI)
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TPS - Advanced Flexible Reusable Surface
Insulation

• AFRSI blankets have replaced the majority of the
  LRSI tiles on the Orbiter's upper surfaces
  because of their superior insulation properties
  and lower weight per surface area
• AFRSI consists of a low-density fibrous silica
  batting made up of the same 99.8-percent silica
  fiber content as the HRSI, LRSI, and TUFI
• An outer woven silica high-temperature fabric
  overlays an inner woven lower-temperature glass
  fabric similar to fiberglass
• Fabric covers both the inside and outside of the
  silica fiber batting by sewing the layers
  together with silica thread
• Sewn fabric produces the quilt-like appearance of
  the AFRSI blankets

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TPS - Advanced Flexible Reusable Surface
Insulation

• Density of the AFRSI blankets is approximately
  8-9 lb/ft3
• Temperature range up to 1,200o F
• Thickness ranges from 0.45 to 0.95 in.
• Like the RCG silica tiles, the thickness of the
  blanket depends on the highest temperatures
  encountered on the surface during reentry

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AFRSI Fibrous Insulation Blankets
A
Quartz OML Fabric
Quartz OML Thread
A
RTV Transfer Coated Surface on IML
OML Thread
Quartz Batting
B
B
D
View B-B
OML Thread
D
OML Fabric Folded Over To IML and Stitched
Through Thickness
C
C
Glass IML Fabric
Section A-A
IML Thread
View C-C
OML Thread
OML Thread
OML Fabric
Batting
IML Fabric
IML fabric
Glass IML Thread
IML Thread
E
Detail E
Section D-D
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Fibrous Refractory Composite Insulation (FRCI)
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TPS - Fibrous Refractory Composite Insulation
(FRCI)

• The FRCI-12 HRSI tiles are a higher strength tile
  than the pure silica HRSI tile
• Derived by adding AB312 (alumina-borosilicate
  fiber), called Nextel, to the pure silica tile
  slurry

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Felt Reusable Surface Insulation (FRSI)
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TPS - Felt Reusable Surface Insulation (FRSI)

• FRSI is the same Nomex material as SIP pads used
  to bond the HRSI, LRSI, TUFI and FRCI tiles to
  the Orbiter's skin
• The FRSI varies in thickness from 0.16 to 0.40
  inch depending on the heat load encountered
  during reentry
• Consists of sheets 3 to 4 feet square, except for
  closeout areas, where it is cut for an exact fit
• FRSI is bonded directly to the Orbiter surfaces
  by high-temperature RTV adhesive

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TPS - Felt Reusable Surface Insulation (FRSI)

• The  normally porous Nomex felt is waterproofed
  by a silicon elastomer coating impregnated with a
  white pigment to provide required thermal and
  optical properties
• FRSI blankets that cover nearly 50 of the
  Orbiter's upper surfaces has an emittance of 0.8
  and solar absorptanace of 0.32

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Gap Fillers
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TPS - Gap Fillers

• Gaps in the TPS tiles and tile boundaries are
  protected from high-pressure, high-temperature
  reentry plasma by braided fiber or cloth
  containing alumina-borosilicate fiber (AB312, or
  Nextel)
• Several examples of the gaps requiring protection
• HRSI, FRCI and TUFI intratile gaps
• Nose cap outer edge
• Windshield edges
• Escape hatch edges
• Elevon trailing edges

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Gap Fillers
Nextel Ceramic Fabric
Nextel Sleeving
Saffil Alumina Batting
Nextel Ceramic Fabric
Saffil Alumina Batting
Inconel Foil
Inconel Foil
Pillow With Sleeving
Pillow or Pad Type
Nextel Ceramic Fabric
Nextel Ceramic Fabric
Saffil Alumina Batting
Saffil Alumina Batting
Nextel Ceramic Sleeving
Inconel Foil
Inconel Foil
Pillow Captive Type (Single Lip)
Pillow Captive Type (Double Lip)
RTV or Ceramic Coated Nextel Fabric
Ames Type
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Thermal Barriers and Seals
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TPS - Thermal Barriers

• Thermal barriers are used in the areas between
  various components and the TPS protective tiles
• Used to prevent hot plasma generated by the
  reentry heating from entering the interior
  through movable components
• Examples of the thermal barrier regions are
• Rudder/speed brake
• Landing gear doors
• Vent doors
• Payload bay doors

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Thermal Barrier and Seal Locations
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Typical Thermal Barrier
Nextel Sleeving
Nextel Fabric
Inconel Spring Tube
RTV-Stiffened Fabric Tail
Typical Thermal Barrier Detail
Thermal Barrier Support
Thermal Barrier Carrier Plate
Structure Side Tile
Thermal Barrier
Main landing Gear Door Side Tile
Main Landing Gear Door Thermal Barrier
Frank Jones NASA, KSC
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Elevon Cove Seal
Upper Wing TPS
Flipper Door Seal
Flipper Door
Elevon Rub Panel
Uncoated AFRSI Blankets
Hinge Pins
Elevon Rub Tube
Lower Wing TPS
Lower Elevon TPS
Pillow Gap Filler
Spanwise Polyimide Primary Seal
0.5 Gap
HRSI Tiles
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Waterproofing
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TPS - Waterproofing/Rewaterproofing

• Each of the Orbiter's TPS tiles and blankets are
  waterproofed when manufactured before delivery,
  and again before each launch, to reduce water
  absorption from the atmosphere and from rain
• The process uses dimethylethoxysilicane (DMES)
  fluid which is injected into each of the tiles
  with a needleless gun
• Blankets are injected with DMES from a needle gun

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TPS Processing
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Orbiter Processing at KSC
Frank Jones NASA, KSC
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Tile Processing
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TPS Repair and Replacement
Out of Tolerance 3.18
Misc. Sector 13.27
Modification 26.30
Access 31.73
Flight 20.42
Ground Handling 5.10
Frank Jones NASA, KSC
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TPS Discrepancies
FRSI, Filler Bar, and All Others 3.56
Gap Fillers, Thermal Barriers, and O/T
Conditions 16.30
FI Blankets 3.50
Re Water Proofing 2.88
RSI Tiles 73.75
Frank Jones NASA, KSC
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Labor Time per TPS Type

• Tile 2.27 hours/sq.ft.
• FIB 0.16 hours/sq.ft.
• FRSI 0.02 hours/sq.ft.
• ET SOFI 0.70 hours/sq.ft.

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Discipline Comparison
Operations 8
Quality Assurance 15
Logistics 3
Engineering 18
Maintenance Technicians 37
Manufacturing Technicians 19
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Beyond Shuttle

• Internal vehicle health monitoring
• RF replaces ground connections
• No penetrations
• No windows
• Self healing TPS

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References
Lance Erickson, Space Shuttle Operations and
Technology, 2007 Donald Curry, David Johnson,
Space Shuttle Development Conference, Thermal
Protection System Technical Session, NASA/Ames
Research Center, July 28-30, 1999 Frank Jones,
NASA-KSC