# Presentation: 666880

**TPS Enhancement Options**
**September 16, 2003**

## Issue

**STS-107 accident has shown that Thermal Protection System (TPS) design is vulnerable to impact damage for conditions outside of current design criteria**
- Decreasing that risk for damage (Orbiter Hardening) is can be addressed by making the structure less vulnerable to impact damage
- Design modification options can address changes which are expected to make the Orbiter less vulnerable to the risk, not abate the overall external risk

## Six Critical TPS Areas Targeted For TPS Enhancements

- WLESS Redesign
- Gear and ET Door Redesign
- Carrier Panel Upgrades To Eliminate Bonded Studs
- Durable Tile (BRI 8, BRI 20)
- Elevon Leading Edge Carrier Panel Redesign
- White TUFI and Vertical Tail AFRSI High Emittance Coating

## 1.  Wing Leading Edge Subsystem– Areas of Concern

**1.  Wing Leading Edge Subsystem– Areas of Concern**

**Lower Access (Carrier) Panel-Box Beam**

- 22 Wing LE RCC & Lower Access
- Panels per wing

## 1. WLESS Redesign TIM Actions 

**Lower Access Carrier Panel Redesign**** **
- Four options require trade study
- Option 1 Stronger Access Panel Fasteners
- Option 2  WLESS Extended Carrier Panel
- Option 3 Box Beam Removal
- Option 4 Simplified Leading Edge Access Panel Installation

**Redesign Insulators to Add High Temperature Insulation  **
**Add Front  Spar Protection**
**Incoflex Insulator Redesign**
**Evaluate use of ****Yttria Zirconia Coating on Surfaces of Insulation Panels**

**Integrated solution can provide additional protection against impact & plasma flow vulnerability:**

## 1.  WLESS Redesign Forward Plan

## 4. Lower Surface Acreage Tile - Issues

**Example of Critical Subsystems with rough overlay of OV-102 STS-87 impacts > 1 inch**
**(overlay scale not exact)**

**Impact damage at adjacent tiles beyond 1 tile and/or at a critical location can result in LOV**
**Post-flight TPS repair is the second longest flow task**
- Lower surface tile average ~ 100 impacts/flight
**Contingency EVA inspection & repair will be difficult & complex**
**Contingency EVA operations will need to be minimized for crew safety**
**Need to assess other available methodologies**

## 4. Tougher Lower Surface Tile (BRI 8/12/20) 

**Complete tougher tile (BRI-8 and BRI-20) development **
- BRI-8 development funded by Upgrades + X-37 (complete December 2003)
- BRI-20 development fully funded by X-37 (complete August 2003)
- Delta Orbiter certification required
- BRI-8 replaces HRSI LI-900
- BRI-20 intended to replace HRSI LI-2200 and HRSI FRCI-12 type tiles
**Complete Ballistic SIP development (partially funded by Shuttle IRAD)**
- Requires additional development funding
- Requires full Orbiter certification
- Goal to keep BRI-8 and Ballistic SIP schedules in parallel
**Define lower acreage tile implementation plan**
- Define methodology to prioritize implementation
- Address low velocity (ascent) impact risk areas
- Address high velocity (MMOD) impact risk areas
**Implement tougher tiles (BRI-20) **
- ET Door periphery, MLGD periphery, NLGD periphery, Elevon Leading Edge and Wing Trailing Edge carrier panel tiles and Window Frames
**Complete BRI-12 development (current minimal dev funding from Orbiter)**
- Requires full Orbiter certification

## 4.  Tougher Lower Surface Tile

## 4.  Tougher Lower Surface Tile (BRI 8/12/20) Forward Plan

## 2.  Landing Gear & ET Door TPS - Issues

**Impact damage to door, frames, TPS & thermal seals can cause LOV**
**Contingency EVA inspection & repair will be difficult & complex**
**Contingency EVA operations will need to be minimized for crew safety**

**2.  Landing Gear & ET Door TPS - Issues**

## 2. Door (MLGD, NLGD, ETD) Redesign

**Door (MLGD, NLGD, and ET Door) seal requirements need to be verified ****- UA Closure Team Recommendation **
- Verified intent to be a pressure seal
- Study required to determine if seals can be verified with existing design
- Potential design modification or other method required to allow seal verification every flight
**MLGD Redesign **
- Fill MLGD corner void
- Thermal Barrier System Redesign
- Redesign MLGD seal design to be similar to Modified NLGD Thermal Barrier Design Approach
- Bond in redundant thermal barriers
- Add preformed insulation to existing and new thermal barriers
- Upgrade thermal barrier material to higher temperature Nextel fabrics
**NLGD Redesign **
- Existing Thermal Barrier Simple Upgrades
- Change thermal barrier batting material to preformed insulation
- Upgrade thermal barrier material to higher temperature Nextel fabrics
**ET Door Redesign**
- Existing Thermal Barrier Simple Upgrades
- Add preformed insulation to existing thermal barriers
- Upgrade thermal barrier material to higher temperature Nextel fabrics

## 2. Door (MLGD, NLGD, ETD) Redesign - MLGD Redesign to Add Redundant Bonded in Thermal Barriers

**NLGD Thermal Barriers are a Redundant System unlike MLGD**
- Multiple Thermal Barriers Provide Backup Capacity
**NLGD Thermal Barriers are bonded to the STR side tile sidewalls, chin panel RCC, and to the Inconel ET Bearing plate bracket located in the center AFT of the door**
- The OML Thermal barriers are bonded with ceramic based adhesive due to high bondline temperature.  IML and Primary Thermal barriers are mainly installed with RTV

- Door Frame
- Upgrade to BRI20

- Thermal Barrier

- Door Tile upgrade to BRI 20

- FRSI

- SIP

- Frame Structure

- Thermal Barrier Support Structure

- SIP

- Door Structure

_**MLGD**_

**Silicone Sponge Seal**

**Environmental Seal**

**Structure Side Tile**

**Door Side Tile**

**IML**

**IML Thermal Barrier**

**Primary Thermal Barrier**

**OML Thermal Barrier**

_**NLGD Thermal Barriers**_

**Implement This NLGD **
**Feature (bonded on thermal barriers) **
**on MLGD**

## 2. Door (MLGD, NLGD, ETD) Redesign – Thermal Barrier Upgrade To Enhance Heat Resistance of TPS

**Use Higher Temperature Capability Fabric in Existing Thermal Barrier Locations **
**Applies to MLGD, NLGD, and ETD**
**Replace Thermal Barrier Fabrics with advanced Nextel (Service Temperature 2900°F)**
- AB312 Fabric is currently used and has a Service Temperature of 2600°F
- Nextel 440 is used on a Rudder Speed Brake Thermal Barrier, Some NLGD areas, and the Chin Panel Gap Filler
- Higher temperature materials increase contingency margins
**Use Preformed Insulation**
- Reduces Variability and Turnaround time
- MLGD and ETD Thermal Barriers do not have Insulation and would Benefit from the use of Preformed Insulation as a Flow Restrictor

**NLGD**

**MLGD**

**ETD**

**ADD INSULATION**

**CHANGE INSULATION**

## 2.  Door (MLGD, NLGD, ETD) Redesign Forward Plan

## 3.  Carrier Panel Redesign To Eliminate Bonded Studs 

**FRCS TPS Carrier Panels - Issues**

**Impact damage to TPS carrier panels or attachments can cause LOV**
**Lost carrier panels can impact critical vehicle areas**
- E.g. FRCS panels into windows during ascent
**In contingency situations:**
- Bonded studs may not respond to impact loads without failure
- Fasteners that have lost torque may release
- Nut plates & inserts that have limited self-locking life may lose torque
- Panels with only 2 fasteners are not fail-safe** **
**No back-up or redundancy if TPS or panel damaged**
**Contingency EVA inspection & repair will be difficult & complex**
**Contingency EVA operations will need to be minimized for crew safety**

## 3. Carrier Panel Redesign TIM Actions

**Eliminate use of bonded studs for future design – UA Closure Team recommendation**
**Perform analysis to ensure positive margins exist if studs are completely de-bonded -– UA Closure Team recommendation**
- Boeing Structures team confirmed bonded studs added since installation was negative margin without
**Define all bonded stud locations installed by MR;  PRCA search currently in-work **
**Redesign if cannot “return to print” to  threaded fasteners for location studs bonded by MR  - UA Closure Team recommendation **
**Determine if increasing fastener size will maintain positive margin if current bonded studs missing**
**Where not possible, study redesign of FRCS carrier panel attachment to add threaded fastener in place of design bonded studs**
- Redesign Tile array pattern as required
- Investigate use of self locking bolts** **
- Investigate feasibility of increasing carrier
- 	panel thickness and/or fastener diameter to
- 	gain margin in lieu of bonded stud elimination

## 3.  Carrier Panel Redesign Forward Plan

## 5.  Elevon Cove Leading Edge Carrier Panel- Issues

**5.  Elevon Cove Leading Edge Carrier Panel- Issues**

**Elevon Coves**

**Example damage on OV-103 STS-51D**

**Elevon Cove & Hinge**

**LE carrier panels are fastened to seal panel using self locking thin wall inserts.  Mods to carrier panels have added tension preload to fasteners**
**Failure of insert or fastener due to impact of other reasons would expose primary seal panel to direct hot gas during entry**
**Contingency EVA inspection & repair will be difficult & complex**
**Contingency EVA operations will need to be minimized for crew safety**

## 5. Elevon Cove Leading Edge Carrier Panel Redesign - Elevon LE Carrier Panel Instl – Redesign TIM Actions

**View A-A Looking Down at Elevon Leading Edge Carrier Panel Installation with Seal Retainer Omitted (Rotated 90° CW)**

**Section B-B Between Elevon Carrier Panels Looking Forward**

**C**

**C**

**Section C-C Between Elevon Carrier Panels Looking Outboard**

**Ablator vs. FRSI between carrier panels & seal retainer panels**

**Nextel Fabric Sleeving in all Leading Edge locations & between panels**

- Seal Retainer Panels

- Carrier  Panel (0.080 inch thick aluminum)

- SIP

**Nextel Fabric Sleeving**

**Gap Filler**

- Tile

**Increase  Original Attachment Bolt Diameter (2/panel)**

**Add 3rd Bolt in Optional Locations (Fwd or Aft)**

_**Design Changes**_
- Increase attachment bolt diameter
- Increase number of  bolts
- Add high temp Nextel fabric sleeving in all Leading Edge locations
- Replace Filler Bar between Carrier Panels with compressible high temp sleeving system
- Investigate filling cavity with Ablator or FRSI

**Support Bracket between panels (0.040 inch thick Inconel)**

## 5.  Elevon Cove Leading Edge Carrier Panel Forward Plan

## 6.  White TUFI – Issues - OMS Pod Fwd Dome & Aft Outboard Corner

- Upgrade to harder White TUFI tile development on-going
- Impact protection can still be increased with thinner 5th-generation tile systems
**“****Cadillac” fitting has low margin at high temperature**
- Does not have heat-sink capability if tile lost

**6.  White TUFI – Issues - OMS Pod Fwd Dome & Aft Outboard Corner**

**OMS Pod Aft Outboard Corner LI-900 and FRCI-12 Tile**

**Tile over “Cadillac” Fitting**

**OMS Pod Dome / Leading Edge LI-900 and FRCI-12 Tile**

## 6. Current LRSI Tile Are Delicate, Frequently Damaged, And Difficult To Access For Repair

**OV-103 & Subs have approximately 700 LRSI tile on upper surface of crew compartment and OMS pods**
- OV-103 & subs have 325 LRSI tiles (average)
- Each OMS (orbital maneuvering system) pod has 196 LRSI tiles
**White RCG (reaction-cured glass) tile coating is used on upper surface to reflect solar energy.  Black RCG is used on lower surface to emit radiation during reentry**
**White RCG coating is more delicate than black RCG on the lower surface tiles, making it more susceptible to damage**
**Forward-facing surfaces of the canopy and the OMS pods are subject to impact damage during ascent**
- OV-102 STS-93 had 31 damages to upper surface, 5 > 1”
- OV-103 STS-102 had 44 damages to upper surface, 4 > 1”
- OV-104 STS-104 had 18 damages to upper surface, 2 > 1”
- OV-105 STS-108 had 14 damages to upper surface, 5 > 1”
**Upper surface locations are more difficult to access for repair and risk tool drop damage**

## 6.  White TUFI TIM Forward Plan

## 6.  Vertical Tail AFRSI High-Emittance Coating

**Vertical tail is limiting factor in contingency trajectories**
- Add current gray high emittance coating to side AFRSI blankets
_**BENEFITS:**_
**Expanded contingency low-alpha reentry  trajectory limits**
**Guidance control assessment for contingency trajectories required in study**
**Impacts of contingency limits to other systems required in study**