NASA Crew Exploration Vehicle, Thermal Protection System, Lessons Learned 6th International Planetary Probe Workshop, June 26th, 2008 CEV TPS Advanced Development Project Office Ethiraj Venkatapathy & James Reuther National Aeronautics & Space Administration Ames Research Center 1 Orion System Elements Orion consists of four functional modules Launch Abort System -- emergency escape during launch Crew Module – crew and cargo transport Service Module – propulsion, electrical power, fluids storage CEV TPS Advanced Development Project Office Spacecraft Adapter – structural transition to launch vehicle 2 Orion vs. Apollo • Orion shape is derived from Apollo, but approximately 30% larger – Presents challenges to the TPS, including: • Increased heat loads • Manufacturing challenges CEV TPS Advanced Development Project Office Comparison of Apollo to Orion floating in still water 3 The Orion TPS Objective Enable the CEV Project Office and the Prime to develop Back shell a CEV heat shield… Heat shield ... by initiating a Orion Lunar direct return (LDR) conditions: Advanced Development • 11 km/s atmospheric entry Project to raise the TRL 2 • peak heat rate > 750 W/cm and reduce the risk of a Orion Low Earth Orbit (LEO) return conditions: Lunar return capable CEV TPS Advanced Development Project Office • 8 km/s atmospheric entry ablative TPS materials • peak heat rate > 150 W/cm2 and heat shield systems 4 Background • The Exploration Systems Architecture Study (ESAS) commissioned in the summer of 2005 settled on a new Constellation (Cx) human space transportation architecture. • At the core of the ESAS recommended architecture was a new Crew Exploration Vehicle (CEV – Orion) that would serve as the US human transportation system for Low Earth Orbit (LEO) as well as lunar missions • A top risk identified by ESAS for CEV was the development of a heat shield and applicable Thermal Protection System (TPS) materials meeting both LEO and Lunar return requirements – Ablative TPS materials required to support LEO and Lunar missions – The US had focused little attention on ablative materials since Apollo era. – All applicable ablative TPS materials were at low technology readiness levels (TRL ~ 3-4) • In Oct 2005, the CEV Project commissioned the CEV TPS CEV TPS Advanced Development Project Office Advanced Development Project to address the heat shield development risk 5 Heat Shield Operating Environments CEV TPS Advanced Development Project Office 6 Orion Heat Shield Components • Carrier structure – Dish section – Shoulder section • Ablative acreage TPS – Block layout – TPS material thickness • Compression pads • Separation mechanism • Main seal CEV TPS Advanced Development Project Office 7 Scope of TPS ADP Primary Objectives • TPS materials fabrication and characterization – Development of material constituent, processing and properties specifications – Detailed mechanical and thermal material properties testing • TPS materials thermal performance capabilities for LEO & Lunar returns – Nominal & emergency entry trajectories – Aerothermal environments – Screening and comprehensive TPS materials thermal performance testing – TPS materials thermal response models – TPS thermal performance margins policy • TPS materials thermal-mechanical performance capabilities – Ground, launch, on-orbit, nominal and emergency entry, descent & landing loads – Thermal-structural integrated (carrier structure + TPS) testing – FEM analysis and design of TPS materials • Design for all heat shield components – TPS acreage, carrier-structure, TPS bonding, compression pads, main seals, gap/seams, close-outs, repairs • Integrated heat shield design and performance capabilities – Integrated design of all components – TPS material lofting and thermal, MMOD and integration sizing – Integrated thermal-structural analysis and design of complete heat shield CEV TPS Advanced Development Project Office • Manufacturing for an integrated 5 meter heat shield – Infrastructure and equipment for full-scale heat shield production (e.g. full scale oven) – Production staffing and resources to produce materials meeting spec. at volume – Demonstration of full-scale heat shield manufacturing procedures 8 Other TPS ADP Objectives • Revitalize the ablative TPS industry: – For the past 25+ years, NASA-sponsored R&D has focused mostly on reusable TPS materials • Ceramic tiles, coatings, blankets (e.g., Shuttle acreage) • Oxidation-resistant carbon-carbon (e.g., shuttle WLE) • Ultra High Temperature Ceramics (UHTCs) – Little work completed on advanced ablative materials, as a consequence, the ablative TPS materials community in the U.S. (very robust in the 60s and 70s) has significantly diminished – NASA is really the only customer for this industry – thus it is vital for NASA to make investments not only internally but also in industry • Train the next generation of NASA entry systems developers – Prior to the CEV development NASA efforts were focused on either basic TPS materials R&D or performing TPS operational support – Limited efforts were applied to perform end-to-end development of a new heat shield systems for flight vehicles CEV TPS Advanced Development Project Office – NASA in house staffing lacked training to perform flight hardware development 9 Initial Materials Development & Selection - Block 2 (lunar), Phase I, Materials - Block 1 (LEO), Phase I, materials CEV TPS Advanced Development Project Office 10 Heat Shield Materials • Block 2 TPS Materials Critical Path for CEV No longer considered for CEV – Boeing / FMI: PICA (Baseline) – Textron: Avcoat (Primary Alternate) – Textron: 3DQP (Alternate) – Boeing: BPA (Alternate) – ARA: PhenCarb 28 – Lockheed Martin / CCAT: Advanced Carbon-Carbon / Calcarb • Block 1 TPS Materials – Lockheed Martin: SLA-561V – Shuttle tile materials: LI-2200, BRI-18 • Carrier Structure – Titanium / Titanium honeycomb (Baseline) – GR-BMI Composite / Titanium honeycomb (Alternate) • Compression Pads – Carbon phenolic CEV TPS Advanced Development Project Office – Fiberglass phenolic – Silica phenolic 11 Candidate Heatshield Ablator Materials for Lunar Return (Block 2) Conditions Vender Heritage Local TPS System TPS ADP Image Material Mission & Approach Construction Contracts Diameter TTT IP Density ARA MDU, TRL = 4 Uniform TTT – Segmented Phase I PhenCarb 28 (2007) 1 m in Honeycomb with seams 450 kg/m3 Boeing / FMI Stardust, TRL = 4 Uniform TTT Blocks/Tiles w/ Phase I, Phase II PICA (2006) 0.9 m bonded with filled 270 kg/m3 RTV/SIP/RTV gaps/seams LM / LCAT Genesis, TRL = 4 Dual layer Monolithic or Phase I ACC / (2004) 1.35 m system segmented 1500 / 180 kg/m3 CalCarb Textron AS-501, TRL = 4 Uniform TTT – Monolithic w/ Phase I, Phase II Avcoat (1967) 3.9 m in Honeycomb honeycomb 540 kg/m3 seams Textron DoD ?, TRL = 3 Dual layer with Segmented w/ Phase I, Phase II 3DQP (?) ? integration tongue & 1600 / 220 kg/m3 layer groove CEV TPS Advanced Development Project Office Boeing Coupons, TRL= 3 Uniform TTT – Monolithic or Phase II BPA (2005) 1 m in Honeycomb segmented 540 kg /m3 12 5 Materials Selected for Block 2 Phase I Screening Tests Coupons Boeing PICA ARA PhenCarb 28 Textron Avcoat CEV TPS Advanced Development Project Office Textron 3DQP Lockheed Martin ACC/CalCarb 13 Block 2, Phase I Testing in Arcjet CEV TPS Advanced Development Project Office 14 Block 2 Phase I Stagnation Arcjet Testing Three arcjet test series were performed • Block 2 peak heating - 1000 W/cm2 @ 30 sec --- Ames IHF • Block 2 skip dual-pulse 400 / 150 W/cm2 --- Ames AHF • Block 1 nominal entry – 130 W/cm2 @ 200 sec --- Ames IHF CEV TPS Advanced Development Project Office 15 Block 1 SLA-561V & Shuttle Tile Status • SLA-561V TPS material performance issues – MSL stagnation thermal ablation testing showed excellent stagnation heating performance up to 300 W/cm2 – However, arcjet tests at low heating (90 – 150 W/cm2), high shear and high pressure (medium enthalpy) conditions showed material failures – Material was dropped from consideration for CEV (7/07) – Mars Science Laboratory (MSL), which had baselined SLA-561V, switched their baseline material to PICA (11/07) • CEV testing of SLA-561V revealed the performance problems for MSL • If it were not for the PICA work by the TPS ADP, MSL would not have had an alternate material system, and would not be flying in 2009 • Shuttle tile material performance issues – Initial coupon testing of Shuttle tiles indicated excellent performance for BRI-18 (coated), LI-2200 (coated & uncoated) – Stagnation arcjet tests of gap/seam articles showed that at LEO heating and pressure conditions the material exhibits gap performance problems – Material was dropped from consideration for CEV heat shield utilization CEV TPS Advanced Development Project Office • Both candidate Block 1 materials have been eliminated from consideration for the heat shield 16 Baseline PICA Development Status CEV TPS Advanced Development Project Office 17 PICA Heat Shield Overview • PICA – Local thickness tailored to heat load • 232 individual sizing points • PICA blocks mounted to axisymmetric carrier structure – Uses +/- 1” OML deviation – Block layout design • RTV-SIP-RTV bond to carrier structure • Gap/Seam configuration not finalized – 16 pcf CEV TPS Advanced Development Project Office 20 inch 10 inch tiles tiles Current ADP Block Layout PICA HS MDU 18 Block 2 PICA Status • Boeing / FMI production of PICA materials – All PICA coupons / panels for NASA testing completed on schedule and within specs – Initially planned PICA material properties testing completed – PICA full-scale