Thermal Wadis: Using Regolith for Thermal Energy Management

Transcription

1 Thermal Wadis: Using Regolith for Thermal Energy Management Kurt Sacksteder, NASA Glenn Research Center Robert Wegeng, Battelle Memorial Institute Nantel Suzuki, NASA Headquarters Annual Meeting of the Lunar Exploration Analysis Group November 16-19, 2009 USRA Lunar and Planetary Institute Houston, TX

2 Thermal Wadis Concept Thermal Wadis use modified regolith as a thermal mass to: Store solar energy for nighttime use and/or Function as a radiator for daytime heat rejection Radiant Energy Reflector Sunlight Radiant Energy Reflector (Heat-Loss Shield) Rover Rover Thermal Mass Thermal Mass 2

3 Outline Performance at Equatorial Sites Performance near the South Pole Lunar Simulant Thermal Property Measurements Thermal Wadi Application Issues Conclusions 3

4 Thermal Wadi Performance Simulations 4

5 Thermal Performance Simulation Thermal properties of native regolith and modified regolith Heat conduction with surface radiative boundary conditions, bounded on bottom/sides with native regolith properties. Solar illumination models specific to location Provisions for steering sunlight and limiting cooling radiative emissions to space Provisions for providing heat to lunar surface assets Properties Native regolith Basalt Rock Thermal diffusivity 6.6 x 10-9 m 2 /s 8.7 x 10-7 m 2 /s Density 1800 kg/m kg/m 3 Specific heat 840 J/(kg K) 800 J/(kg K) Thermal conductivity 0.01 W/(m K) 2.1 W/(m K) 5

6 FY09 Thermal Performance Simulations Equatorial Surface Temperatures q/q max T(K) T max,regolith = 387 K T min,regolith = 117 K t(hr) Solar Illumination of the Lunar Surface: Equatorial Thermal Wadis store solar energy flux in thermal mass then provide nighttime thermal protection Modified regolith: α = Basalt Rock Sun-tracking reflector (1300W/m 2 ) Night-time heat-loss shield Robotic rover heating (25W/m 2 ) Surface Temperature > 247K t(hr) Surface Temperature of Native Regolith T(K) T min, regolith t(hr) T min, nominal T max = 388 K T min = 247 K Surface Temperature of 50cm deep Wadi 6

7 FY09 Thermal Wadi Performance Shackleton Crater Rim Surface Temperatures Solar illumination near the south pole (from H.J. Fincannon) Annual cycle provides many months without eclipse Longest eclipse is 52 hours q/q max q/q m Thermal Wadis can be configured to provide a continuous, moderate temperature heat source Sun Tracking, Heat-Loss Shield, Rover Heating Modest temperatures achieved with managed solar flux input Performance margins Most forgiving location for wadi demonstration T(K) t(hr) T max = 320 K T min = 273 K t(hr) T touch T electronic T min, nominal T min, regolith 7

8 FY09 Thermal Wadi Performance Thermal Animation of Schematic Rover on Equatorial Wadi 8

9 FY09 Thermal Wadi Performance Effect of Lunar Dust Layer on Wadi Surface Temperature Dust layer thickness 0 mm (no dust) 1 mm 2 mm 5 mm Dust layer of small thickness mitigates thermal mass surface temperature swing Dust may actually be beneficial! 9

10 Processed Lunar Simulant Thermal Property Measurements 10

11 FY09 Thermal Property Measurements Informing Thermal Mass Production Methods Native Regolith Apollo Measurements Measurements of sintered and melted JSC-1AF, produced using various process conditions Instrument: Laser-Flash Thermal Diffusivity System 11

12 FY09 Thermal Property Measurements 1150 C Sample, Processed in Argon Atmosphere Scanning Electron Microscopy Crystalline Phases via X-Ray Diffraction: Hematite (Fe 2 O 3 ) Anorthite (CaAl 2 Si 2 O 8 ) Diopside (MgCaSi 2 O 6 ) Fosterite (MgSiO 4 ) Elemental Constituents per Energy Dispersive Spectroscopy 12

13 FY09 Thermal Property Measurements Thermal Radiation/Emissivity Changes during Processing Data informs thermal mass production energy requirements Values calculated using data from a 137 GHz Heterodyne Dual- Receiver Millimeter Wave Radiometer Interferometer 13

14 Thermal Wadi Application Issues 14

15 Issues 1. What thermal mass manufacturing techniques lead to reliable, affordable thermal wadi systems? 2. What is the potential to produce electrical power using energy stored in the thermal wadi? 3. What science experiments and technology demonstrations can be operated from a thermal wadi? 4. What are appropriate interfaces between thermal wadis and lunar assets (e.g., thermal connection, comm, power, etc)? 5. Are there opportunities to utilize natural thermal wadis? 6. Can rovers without radioisotopes survive extensive periods of darkness without an external heat source? 7. Can compact rovers carry instruments that will yield data of interest with regard to lunar science and resource prospecting objectives? 8. Can the cost of rovers be reduced by offloading functions that can be provided by a simple lunar infrastructure? 9. Would a thermal wadi infrastructure enhance the business models of Lunar X- Prize participants? 10. Are investments in thermal wadis or other thermal energy storage modes for the Moon relevant to terrestrial energy storage? 11. What is an appropriate way to structure a wadi/rover development and application program so that Education stakeholders are served? 12. What is an appropriate way to structure a wadi/rover development and application program so that Global Partnerships are served? 15

16 National Aeronautics and Space Administration Thermal Mass Production In-Situ Vitrification/ Joule heating Reduction of Regolith/ O2 Production Lightweight Solar Concentrators 16

17 Bi-Modal Rover Courtesy of Heather Jones, Carnegie-Mellon University Lunar Day Radiator rejects heat to space Rover insulated from high temperature regolith Lunar Night Rover absorbs heat from Wadi Reflector retains heat from robot and Wadi Multi-Layer Insulation Regolith Wadi 17

18 Additional Applications of Thermal Wadis A thermal mass can be configured in an artificial PSR to serve as a daytime heat sink. Thermal mass pairs can be configured as high-temp/ low-temp reservoirs, joined with a Sterling generator for electrical power. Insulating Regolith Cooled Thermal Mass 18

19 Resource Characterization: Paving the Way for Humans to Return to the Moon Robotic prospectors, based from thermal wadis, identify resource concentrations & sites Promising sites are selected for near-term lunar resource extraction demonstrations Oxygen from regolith Water and other Volatiles ISRU technology demonstrators, operated at thermal wadis, further reduce cost and performance risks Architectural and engineering studies evaluate the economic potential of lunar resources Humans return to the Moon with clear value driven goals: Site location, work objectives, necessary infrastructure, tools and instruments. 19

20 Conclusions Thermal Wadis use modified lunar regolith as a thermal energy storage medium for nighttime support or daytime heat rejection Thermal Wadis are one way to extend the useful lifetime of lunar surface assets in the face of extreme thermal loading Thermal Wadis can be part of an infrastructure placed on the moon to support both precursor robotic missions and subsequent human operations 20