Orbiter Passive Thermal Protection System

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

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

Orbiter passive thermal tile types 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).

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

Leading Edge Structural Subsystem (LESS)

Leading Edge Structural Subsystem (LESS)

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

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

Reinforced Carbon-Carbon (RCC)

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 Low porosity

TPS - RCC Coating Substrate

TPS - RCC RCC panels and T-seal

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

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

Leading Edge RCC Frank Jones NASA, KSC Fixed Upstream Gap Between Panel and Tee Seal A A E E HRSI Tiles Section A-A Variable Downstream Gap Between Panel and Tee Seal For Thermal Expansion Allowance Upper Wing B B Detail D Interface Gap Between RCC and HRSI Tiles Section B-B 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 Upper Left Wing Wing Spar 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

TPS – LESS RCC Flight Damage Pinhole formation Sealant loss Convective mass loss Micrometeoroid / orbital debris impact damage

RCC Repair/Replacement

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

High-temperature Reusable Surface Insulation (HRSI)

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

HRSI Tiles - Black RCG Coating 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

Tile Configuration

HRSI tiles range in thickness from about one inch to five inches 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

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

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

HRSI tile count on each Orbiter (as of 2002) 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

Toughened Unipiece Fibrous Insulation (TUFI)

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

Low-temperature Reusable Surface Insulation (LRSI)

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

Advanced Flexible Reusable Surface Insulation (AFRSI)

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

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

AFRSI Fibrous Insulation Blankets Quartz OML Fabric Quartz OML Thread A RTV Transfer Coated Surface on IML Quartz Batting OML Thread B B D View B-B OML Thread OML Fabric Folded Over To IML and Stitched Through Thickness D 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 Section D-D Detail E

Fibrous Refractory Composite Insulation (FRCI)

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

Felt Reusable Surface Insulation (FRSI)

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

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

Gap Fillers

Several examples of the gaps requiring protection 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

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

Thermal Barriers and Seals

Examples of the thermal barrier regions are: 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

Thermal Barrier and Seal Locations

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

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

Waterproofing

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

TPS Processing

Orbiter Processing at KSC Frank Jones NASA, KSC

Tile Processing

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

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

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.

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

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

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