1. Advances in Thermal Protection System Instrumentation for Atmospheric Entry Missions Johnny Fu Sierra Lobo, Inc. NASA Ames Research Center Presentation for the University of Idaho April 24, 2008

2. Outline What is thermal protection system (TPS) instrumentation? TPS instrumentation past, present, and future What are the day-to-day activities for TPS instrumentation? Summary Questions

3. What is TPS Instrumentation? Thermal protection system – The material used to protect a spacecraft from the heat encountered when entering an atmosphere – Most well-known example are Space Shuttle tiles – Any spacecraft entering an atmosphere requires TPS to survive – Temperatures can get up to 2300° F for the Space Shuttle TPS tiles on the space shuttle wing Mars Exploration Rover during entry into Mars’ atmosphere

4. Role of Instrumentation The use of instrumentation helps answer some fundamental questions about TPS and atmospheric entry: – How did the material perform in flight? – How hot did the vehicle get? – What was the pressure on the spacecraft? Answering these questions helps improve the design of spacecraft for future missions Without knowing the answers, a future mission carries risks for flight – risks that can be reduced with data returned from instrumentation

5. History of TPS Instrumentation - 60’s Fire II mission - launched in 1964 – Calorimeters to measure heating rate – Radiometers to measure shock layer radiation Fire II capsule – 0.67m diaCross-section showing radiometer location

6. History of TPS Instrumentation - 60’s Apollo IV and VI - launched in 1967 and 1968 – Unmanned test flights for Apollo program – Used ablative TPS material (Avcoat) – Radiometers to measure shock layer radiation – Pressure ports to measure local pressures on the vehicle Diagrams of Apollo TPS instruments (NASA TN D-6843)

7. The Galileo Probe Galileo probe launched in 1989 and descended into Jupiter in 1995 Entered into the atmosphere at > 47 km/s experiencing heating rates on the order of 35 kW/cm 2 - 70 times that of Apollo! TPS contained Analog Resistance Ablation Detectors (ARAD) to measure TPS performance

8. Space Shuttle The Space Shuttle is unique compared to other vehicles described because it uses non-ablative TPS material and has a different shape Instrumentation of early test flights had many thermocouples to measure temperature response Aerodynamic performance of the vehicle determined through arrangement of pressure ports known as a flush air data system Key challenge was to design a way to penetrate the shuttle nosecap without compromising the vehicle Penetration provided pathway to measure surface pressure

9. Mars Science Laboratory Mars Science Laboratory (MSL) is the next-generation Mars rover scheduled to launch in 2009 Instrumentation package known as MSL Entry, Descent, and Landing Instrumentation (MEDLI) Data gathered will help to support design of future missions Increase knowledge of atmospheric data, aerothermal heating models, and TPS performance through use of thermocouples, TPS recession sensors, and pressure sensors Recession sensor AIAA-2008-1219 Pressure sensor NASA 20080013510 MEDLI components NASA 20080013510

10. Future Missions Most prominent mission for TPS instrumentation in the near- future is the Crew Exploration Vehicle – Orion – Flight tests for Orion will need to demonstrate that TPS is certified for use by astronauts returning from the moon Missions to outer planets and moons will require TPS and are also candidates for instrumentation

11. Future Sensor Designs Wireless sensors Micro-meteor impact detection Ultrasonic recession sensors Fiber-optic based spectral measurements

12. Challenges for TPS Instrumentation Instruments need to survive harsh space environments Electronics can undergo extreme exposure to radiation (possibility to induce latch-up on active components) Temperature limits for TPS instruments are extreme indeed – Cruising through space at ~-150 °C – Entering atmosphere at > 1000 °C Mechanical and structural loads during launch and entry are severe as well (3000g of shock) Planetary protection concerns

13. Case Study – Recession Sensor Hollow aErothermal Ablation Temperature (HEAT) sensor Measures recession through change in resistance Patent-pending design: hollow polyimide tube filled with TPS core of choice Requires external constant current source excitation Initial electrical connection formed with resistance weld operation Lead wires are welded; polyimide tube slid over the top for insulation

14. How is this Work Carried Out at NASA? Aerial photo of NASA Ames Research Center Moscow NASA Ames

15. Disciplines Involved Mechanical and electrical design Manufacturing Testing Modeling Project management Many others…

16. Design Engineers and scientist develop requirements for instruments and translate these into a detailed design – interative process Common tools include SolidWorks for mechanical models, MS Office for communication and documentation Example of SolidWorks design for TPS sensor

17. Manufacturing People involved in assembly perform hands-on work to build sensors Use variety of materials including epoxy, bonding agents, wiring, and TPS Work with microscopes, welders, and precision hand tools

18. Testing Arc Jet facilities simulate the severe heating environments of atmospheric entry Variety of disciplines required to support testing including test engineers, mechanical technicians, instrumentation specialists, electricians, and photographers Photos of the Ames Arc Jet facility and testing

19. Modeling Computational modeling of entry environment conditions performed by personnel working in computational fluid dynamics, supercomputers, and software development CFD plot for MEDLI NASA Ames Columbia supercomputer facility

20. Managing it All Project managers develop the project plans, schedules, budgets, and provide the organization to successfully complete the mission Must communicate with all the different variety of disciplines described earlier and more

21. Summary TPS protects a space vehicle from the harsh environments of atmospheric entry TPS instruments measure the environments and performance of the material Integrating TPS instruments onto a space vehicle poses unique challenges not found on the ground Successful use of instruments requires the contribution of all kinds of personnel at NASA

22. Acknowledgements In-Space Propulsion program (ISP) CEV TPS Advanced Development Project Mars Science Laboratory Entry, Descent, and Landing Instrumentation Lunar re-Entry Experiment

23. Questions Questions? Johnny Fu, Electrical Engineer, johnny.fu@nasa.gov johnny.fu@nasa.gov NASA Ames Research Center - www.arc.nasa.gov www.arc.nasa.gov