1. Orbiter Passive Thermal Protection System

2. 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

3. 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

4. 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).

5. 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

6. Leading Edge Structural Subsystem (LESS)

7. Leading Edge Structural Subsystem (LESS)

8. 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

9. 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

10. Reinforced Carbon-Carbon (RCC)

11. 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

12. TPS - RCC
Coating
Substrate

13. TPS - RCC
RCC panels and T-seal

14. 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

15. 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

16. 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

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

18. RCC Repair/Replacement

19. Bonded TPS HRSI tiles on the Orbiter ~19,700 (9 lb), 525 (22 lb)
TUFI tiles on the Orbiter (8 lb)
FRCI tiles on the Orbiter ,950 (12 lb)
LRSI tiles on the Orbiter (9 lb), 77 (12 lb)
FIB blanket area on the Orbiter ,123 sq ft
FRSI sheet area on the Orbiter ,024 sq ft

20. High-temperature Reusable Surface Insulation (HRSI)

21. 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

22. 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

23. Tile Configuration

24. 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

25. 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

26. 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

27. 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

28. Toughened Unipiece Fibrous Insulation (TUFI)

29. 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

30. Low-temperature Reusable Surface Insulation (LRSI)

31. 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 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

32. Advanced Flexible Reusable Surface Insulation (AFRSI)

33. 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

34. 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

35. 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

36. Fibrous Refractory Composite Insulation (FRCI)

37. 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

38. Felt Reusable Surface Insulation (FRSI)

39. 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

40. 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

41. Gap Fillers

42. 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

43. 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

44. Thermal Barriers and Seals

45. 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

46. Thermal Barrier and Seal Locations

47. 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

48. 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

49. Waterproofing

50. 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

51. TPS Processing

52. Orbiter Processing at KSC
Frank Jones NASA, KSC

53. Tile Processing

54. 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

55. 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

56. Labor Time per TPS Type
Tile = hours/sq.ft.
FIB = hours/sq.ft.
FRSI = hours/sq.ft.
ET SOFI = 0.70 hours/sq.ft.

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

58. 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

59. 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