Thermal performance evaluation of ultra-light space solar power satellite for GEO and LEO orbits

Transcription

1 Thermal performance evaluation of ultra-light space solar power satellite for GEO and LEO orbits IEEE WiSEE, December, 2018 T. Vinogradova, PhD M. Milligan, M. Kruer, A. Messer NGAS Space System Division, Military and Civil Space

2 Thermal performance evaluation of SSP satellite Agenda Background SSP Thermal Model overview Model details and assumptions Model optical and material properties Thermal analysis results for LEO and GEO orbits Conclusions Collaborators Pilar Espinet-Gonzalez, Nina Vaidya, Tatiana A. Roy, Emily C. Warmann, Ali Naqavi, Samuel P. Loke, Jing-Shun Huang, Christophe Leclerc, Terry Gdoutos, Ali Hajimiri, Sergio Pellegrino, and Harry A. Atwater 2

3 Past and Current SSP Concepts Mono concepts Modular concepts 3 Recent 5.8 GHz Derivative of original NASA 1979 Reference System Concept Sandwich module concept Ref: J. Mankins, P. Jaffe SSP concept, Integrated symmetrical concentrator: Two reflectors assembles Sunlight is directed to PV array, which is adjusted to transmitter NASA 2012 SSP Arbitrarily Large Phased Array (ALPHA) Concept, J. Mankins Modular concepts with concentrators: Pro: Improved economy via mass production Reduced launch mass and PV cost ultra-light approach Con: Thermal challenge

4 Space Solar Power Ultra-light approach Summary: Space Solar Power concept aims to collect the solar power on board of the satellite, convert it to microwave energy, and wirelessly transmit to earth for on-ground collection Ultra-light approach: Enabling technologies High efficiency ultra-light photovoltaic (PV) Ultra-light deployable space structures Phased Array and Power Transmission Integration of concentrating PV, radiators, MW power conversion and antennas in single cell unit (SSPI tile) Localized electronics and control for system robustness, electronic beam steering Identical spacecraft flying in formation Specific power >1000W/kg to be cost competitive Thermal management of such a system is among key factors for optimal operation to maximize power density (W/kg). 4

5 SSPI Tile Functionality & Structure SSPI Functionality Sun light collected by top surface of tile IC converts DC power to RF controlling phase and polarity Antenna on bottom surface transmits RF power Single tile prototype was build and tested at ambient in 2016 Compact Design Concentrating photovoltaic (CPV) unit Structural support Integrated Circuit (IC) Ground plane with patch antennas Power Collection Each parabolic trough concentrator focuses light onto the adjacent concentrator. A photo-voltaic cell at the end of the concentrator converts the incident light into DC power. DC power is carried to the backplane through electrical traces on the back of each concentrator. Figure: SSPI Tile unit schematics Ref: M. Kelzenberg et al., Ultralight Photovoltaic Concentrator Tiles for the Space Solar Power Initiative, International Space Power Workshop, Aerospace Corporation, 2016 CPV unit Thin parabolic concentrating mirrors: Membrane or carbon fiber materials High efficiency PV cells located on the back of the neighboring mirrors: Spectrolab XTJ cells were used for tile prototype and initial thermal modeling Tile prototype demonstrated successful end-to-end operation at ambient conditions in the laboratory environment 5

6 SSPI Power Collection Thermal management challenge SSPI Concentrating Photovoltaic Tile Concept Pro: Reduced mass and PV cost Con: Thermal management challenge 6 Cover glass development Rad hard cell design Thermal management material development Advanced Concentrators and concentrators thermal and management technology thermal management development Thermal Management Challenge: Heat path from the solar cell with thin, light weight structures Solution: High reflectance inband, high emissivity out-ofband, high thermal conductivity materials Technology focus areas: III-V Multi Junction Solar cells advanced design Advanced glass coating options Concentrators design Flexible thin film specular reflectors optical properties and long term performance Thermal management solution

7 Thermal management Thermal Balance Concentrator absorbs a small amount of sun light. ( W/m 2 ) Reflected Light is absorbed by the PV. What is Solar not converted to DC power is Concentrated converted Irradiance to heat. ( W/m 2 ) DC power is carried to the IC. What is not converted to RF power for Absorbed transmission is converted to heat. ( W/m 2 ) Thermal Management DC Power Heat RF Power Heat 7 Solar irradiance is 1366 W/m 2 at the top of the atmosphere Challenge to get heat away from solar cell and integrated circuit with thin, light weight structures Concentrator material must be multifunctional to maintain cell temperature below 100 C and include: Front and rare emissive surface (e > ) Broadband, specular reflector Heat spreader PV cell interconnect traces

8 SSPI Tile thermal simulation Introduction Thermal model was developed for optimization and trade studies of initial SSPI tile unit (NG Caltech collaboration effort) Tile mockup in Thermal Desktop We prioritized understanding the key material and component selection and its effect on the temperature tolerance and overall system mass SSP satellite was modeled as a large repetitive structure of single tile units, simulating a center tile with a higher fidelity to incorporate proper boundary conditions Model assumed SSP satellite trackers on X and Y axis for precise sun pointing aligned with Z axis Final results were summarized as maximum temperatures and gradient profiles for the center tile unit Model provides an initial estimation of thermal performance for the key tile components and interfaces for trade decisions and future design update 8

9 SSPI Thermal Model Overview Modeling Software Thermal Desktop / SINDA 5.8 Model Model is constructed with carbon fiber and membrane mirrors for comparison Reflector supports, springs, ground & antenna plane frames are from carbon fiber Traces to IC and interconnects are in the preliminary design Orbits analyzed Low Earth orbit (LEO) Geosynchronous orbit (GEO) CFRP materials analyzed T800 4-ply ( configuration) T800 8-ply (( )s configuration) YSH-70A-60S 4-ply ( ) configuration Figure. Fabricated CF mirror, Caltech Ref: N. Vaidya et al., Carbon fiber mirrors for Solar applications, PVSC, 2017 Material Property k W/m- K C p J/kg- K ρ g/cc T800 Carbon Fiber YSH-70A-60S Carbon Fiber

10 LEO Orbit Results LEO orbital parameters Orbit Inclination 98.7, RAAN 90 Altitude 833km, period sec Beta angle 81.3 (no eclipse) Preliminary electrical power contacts are considered Lower reflector temperature for YSH- 70A60S CF mirror material YSH-70A-60S CFRP Heating Rates Solar Flux 1366 W/m² Albedo IR Planet shine 262W/m² +Z face tracking sun Higher ground plane temperature remains T800 CFRP 10

11 GEO Orbit GEO orbital parameters Geosynchronous Altitude km, period 24hr Beta angle -8.7 (no eclipse) Preliminary electrical power contacts are considered Smaller temperature gradient remains for YSH-70A60S CF mirror material YSH-70A-60S SSPI Tile with CF mirrors Heating Rates Solar Flux 1366W/m² Albedo 0.2 IR Planetshine 279W/m² +Z face tracking sun T800 CFRP 11

12 SSPI Tile thermal simulation Summary results Table below shows summary results for SSPI tile 3D thermal simulation. Temperatures are shown as a maximum temperatures at key tile locations. Results are preliminary, and provided for initial trade studies. Case Reflector Type PV cell Reflector Ground Plane LEO Orbit T800 4-ply 398K (125 C) 396K (123 C) 366K (93 C) YSH-70A-60S 4-ply 384K (111 C) 382K (109 C) 375K (102 C) T800 4-ply 391K (118 C) 389K (116 C) 359K (86 C) GEO Orbit YSH-70A-60S 4-ply 377K (104 C) 375K (102 C) 368K (95 C) Membrane mirror with high emissivity front coating 398K (124 C) 396K (122 C) 364K (90 ) Per initial thermal simulation maximum temperatures are in a tolerable range for continuous operation at GEO and LEO orbits 12

13 Conclusions We present simulation results for thermal analysis of ultra-light space solar power satellite operating on GEO and LEO orbit The effort includes characterization of membrane and carbon fiber mirrors for two types of materials Major focus was on two CF reflectors: T800 carbon fiber and YSH-70A-60S carbon fiber Temperatures and temperature gradients: PV cell temperature is ~2 degrees greater than reflector max and ~104 C for YSH-70A-60S 8-ply improved T800 reflector temperature by 7 degrees It was found that maximum temperatures for CPV mirrors, solar cells, IC and ground plane are in tolerable ranges for two types of carbon fiber materials used in initial assessment The simulation successfully demonstrated potential for acceptable thermal performance for ultralight SSPI approach for a set of materials and provided initial estimation for trade decisions in the thermal design 13

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