A Gigawatt-Level Solar Power Satellite Using Intensified Efficient Conversion Architecture Brendan Dessanti Shaan Shah Narayanan Komerath Experimental Aerodynamics and Concepts Group School of Aerospace Engineering

2 Conference Papers from Our Team B. Dessanti, R. Zappulla, N. Picon, N. Komerath, “Design of a Millimeter Waveguide Satellite for Space Power Grid” N. Komerath, B. Dessanti, S. Shah, “A Gigawatt-Level Solar Power Satellite Using Intensified Efficient Conversion Architecture” N. Komerath, B. Dessanti, S. Shah, R. Zappulla, N. Picon, “Millimeter Wave Space Power Grid Architecture 2011”

3 Outline The Space Power Grid Architecture Girasol Converter Satellite Conceptual Design Gas Turbine Comparison with Broadband PV Girasol Satellite Mass Summary and Design Conclusions Mirasol Reflector Satellites Girasol Effect on Architecture Analysis Conclusions

4 Space Power Grid Architecture Phase I Constellation of LEO/MEO Waveguide Relay Sats Establish Space as a Dynamic Power Grid Phase II 1 GW Converter Satellites – “Girasols” Gas Turbine Conversion at LEO/MEO Phase III High Altitude Ultra-light Solar Reflector Satellites – “Mirasols” Direct unconverted sunlight to LEO/MEO for conversion

5 Space Power Grid Architecture Deviations from Traditional Approaches Use Primary Brayton Cycle Turbomachine Conversion of highly concentrated sunlight (InCA: Intensified Conversion) Specific Power, s Separate the collection of sunlight in high orbit from conversion in low orbit Antenna Diameter Millimeter Wave Beaming at 220GHz Antenna Diameter Use Tethered Aerostats Efficiency Through Atmosphere Power Exchange with terrestrial renewable energy Cost to First Power Barrier

6 Girasol Converter Satellite Conceptual Design Conceptual Design of a 1-GW Converter Satellite What it must do? Receive large quantities of directed sunlight, convert, and beam power as millimeter wave Maximize efficiency of conversion Minimize heat that must be radiated Maximize specific power (power beamed /unit mass) launch costs

7 Gas Turbine vs. Broadband PV Conversion Potential for Order of Magnitude Improvement Using Gas Turbine

8 Gas Turbine vs. Broadband PV Conversion Broadband PV scales linearly Specific Power of High Intensity PV arrays limited by heat radiation problem Why? Sun Intensity = Heat That Must Be Radiated = ATCS Mass Fundamental Broadband PV issue: Broadband energy must penetrate a solid surface layer before photons can drive electrons through the semiconductor array

9 IηCA Intensified Efficient Conversion Architecture 1.Primary Brayton Cycle Conversion 2.Optional Narrowband PV Conversion Attempt to achieve 50% efficiency at ground, thus each girasol collects 2GW directed sunlight Given high Brayton Cycle efficiency and high specific mass of mechanical to electrical converter not cost effective to use narrowband PV conversion

10 Girasols

11 Closed Helium Brayton Cycle Helium High and Constant Specific Heat High Thermal Conductivity Low Mass Flow Rate Required Closed Helium Brayton Cycle Operating In Space Starting Point: Intercooled Helium Brayton Cycle Liquid Fluoride Nuclear Power Plant Cycle (DOE - ORNL) Eight 125MW Sections – Dimensions similar to jet engines Alloys exist that can meet 3650K Operating Temperature Advantages over terrestrial jet engines: 1.Predictability of orbit 2.No atmosphere 3.Temperature in space

12 Girasol Turbomachinery 1)300m Collector 2)Intensified Feed 3)Heater 4)Compressor 5)Turbine and Generator 6)Radiator 7)Phase Array Antenna Components:

13 Thermodynamic Cycle Analysis Efficiencies Based on Jet Engine Efficiencies

14 Girasol Satellite Mass Budget and Cycle Analysis ElementMass, kgPercent Collector3, Cooling Sys.168, Brayton Cycle20, AC Generator50, Cryogenics20, GHz Amp.17, Antennae20, Propulsion170, Misc.30, Structure56, Total Girasol567,000 Total Mirasol53,000 Total Mass620, K He Gas Turbine Cycle Analysis

15 Mirasols High Altitude (GEO or Near GEO), Ultralight Reflector Satellites direct sunlight to girasols Utilize technology similar to solar sails Optical linking between mirasols/girasols Sunlight wavelengths on order of μm very little beam divergence, even over large distances

16 Girasol Satellite Design Conclusions 1.By separating solar spectrum, narrow band PV conversion can extract roughly 14% of total solar power as DC 2.Narrowband conversion of pre-separated spectrum minimizes active thermal control requirement 3.Closed Brayton Cycle can achieve over 80% conversion of remaining solar spectrum to AC electrical power 4.Given high Brayton Cycle efficiency and high specific mass of mechanical to electrical converter, not cost effective to use narrowband PV conversion 5.Superconducting generators needed to achieve high power per unit mass needed for mechanical to electric power 6.IηCA Architecture with Brayton Cycle converter and superconducting AC generator offers specific power >1.6 kW/kg vs. <0.2 kW/kg for PV architectures 7.Future Improvements and refinements could lead to >3.4 kW/kg –A potentially revolutionary impact 8.If roadblocks encountered with heat rejection systems, could use spectral separation and narrowband conversion with PV to increase specific power

17 Technical and Economic Results Analysis: Breakeven vs. Selling Price Baseline: SPG Architecture presented at March 2011 IEEE Aero Conf IηCA: Current architecture including Iηca Concept For Given Price of Power, Significant Improvement in Viability

18 Technical and Economic Results Analysis: Girasol Effect on NPV Trough Amount of Investment Required Reduced Significantly from Baseline

19 Conclusions: Girasol Effect on Architecture Summary 1.Girasol Brayton Cycle IηCA offers far better efficiency and specific power, and shorter technology path, than previously considered direct conversion options 2.Girasol Brayton Cycle IηCA greatly improves SSP viablity 3.IηCA can achieve breakeven by Year 31, with NPV trough <$3T, at $0.11/kWh

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