The document discusses the technical challenges facing the development of space solar power (SSP). Key points include: 1) SSP could help address global energy needs and climate change by providing large-scale carbon-neutral energy from geostationary orbit. 2) Major challenges include developing technologies for very large solar arrays and wireless power transmission over long distances from space to Earth. 3) Significant improvements have been made, but constructing multi-gigawatt SSP systems will require overcoming challenges in areas like lightweight structures, high-power wireless power transmission, and modular satellite assembly and deployment.

1. The Technical Challenges for Space Solar Power Neville I. Marzwell, Ph.D. Advanced Concepts - Technology Innovations NASA- Jet Propulsion Laboratory [email_address] September 2007

6. GLOBAL CARBON FUEL REPLACEMENT- 2005 AD Estimated values primarily from EIA projections

7. DoD, National, and International Impact Invest, Survive, Flourish and Grow – A Future History Export Markets SBSP Stable Population Wireless Power Transmission OMV Industrialization Tourism Stellar Probe Hurricane Diversion Asteroid Defense Space Radar Traffic Control “ Dredge Harbor” Beamed Propulsion Sustainable Civilization Nations develop Less Poverty Demographic Transition Reduce GHG Reduce Conflict Stable Climate Tether Telecom Travel Reusable Launch Vehicle Directed Energy ISRU Energy Infrastructure Clean Energy Growth in GDP

8. Capabilities and Challenges If this has been looked at before, what’s changed?

11. SSP - Technology Subsystem Elements 1.2 GW Power to Local Distribution Overall Dimensions: ~5 km x ~15 km 6.5 km x 8.5 km Rectifying Antenna (Rectenna at 5.8 GHz) High Power Density Microwave Beam Structural Elements Solid State WPT Multi-Bandgap PV Optical Elements RF Elements Power System Elements Logistical Materials Low Power Density Microwave Beam Placed in Earth Geo-stationary Orbit Typical Scenario Large SPS in GEO (e.g., 24 Satellites & ~30 GW Total) Microwave Power Transmission (2.45 GHz or 5.8 GHz) Power ~ 1.2 GW (Delivered on the Ground at Remote Locations)

12. Launch Challenge: Costs Will Benefit From Economies of Scale Courtesy of Mr. Gordon Woodcock Disregard this curve, it was added by someone else Expendable Launch Vehicles Fully Reusable Launch Vehicles

13. Solar Power Satellite can be Modular

14. Technology has improved, even more since 1989, oil is now over $75 per barrel and rising Size and Structural Challenge: Technology is maturing fast for possible size reduction

16. Base and Peak Loads…Need Power Storage

18. Orbits : SPS in Geosynchronous orbit. ~ 1980 Reference System

20. GEO, LEO vs. MEO (Part 1) • GEO: Proposed 1980 - Higher launch cost versus MEO/LEO - Very large path distance requiring antenna/rectenna sizes which far exceed the state of the art frequencies (2.35 GHz, 5.8 GHz) • LEO Benefits: Proposed IAF 2006 - Lower launch cost (7 times cheaper per Kg) - Shorter beam path distance (500 km vs. 35,680 km) - Antenna sizes 70 times smaller • LEO Challenges - Orbit used by communication satellites - Adaptive beam steering, requiring a sophisticated phase array antenna to track rectenna on the Earth with very large relative motion velocity, while simultaneously tracking the sun - Lack of solar illumination (50% darkness), difficulty rejecting heat - Only a small area of the Earth can be covered which necessitates large number of satellites (12) compared to (3) for GSO • MEO offers the benefits of GEO at lower cost - Altitude of 11,000 - 12,000 km : radiation level low, costs are modest, orbital period of about 6 hrs, so sun synchronous orbit can be achieved with 4 orbits per synodic day - Minimum constellation of 4 satellites in 2 orbital planes. Each orbital plane is orthogonal to the ecliptic, and orthogonal to the orbit plane. Each satellite orbit is inclined at 66.7 degrees to the equator. The ecliptic is the Earth’s orbit around the sun which is at an angle of 23.3 degrees to the Earth’s equator

23. Rectenna from above

24. CHALLENGE: SSP Wireless Power Transmission Technology Accomplishments : 1. Developed WPT Link Budgets for three 5.8 GHz Systems using Klystrons, Solid State Devices and Locked Magnetrons. 2. Formed NASA WPT Working Group with weekly telecons involving up to 6-NASA Centers, 4-Univ., 4-Industry members, covering Microwave, Laser and Redirected Sunlight WPT systems. Most emphasis on microwaves, but some Lasers. 3. Began NRAs on circularly polarized rectennas, Texas A&M, GaN Class-E amplifier, Rockwell Science Center, Light weight phased array module study, Boeing Phantom Works and a table-top retrodirective phased array demo for public demo, JPL. Demo phased array at JPL terminated due to X3-cost growth. Low-cost phased arrays is an oxymoron. 4. Developed white-paper on SSP spectrum allocation issues as follow on to SSP Question submited to ITU from Study Group 1A. 5. Performing detailed investigation into high-power microwave waveguide and filters multipacting breakdown margins. (Multipacting=RF synchronous, reinforced multiple electon impacts into parallel electrodes in a hard vacuum yielding secondary emission cascade resulting in an RF short circuit. Fixes are to modify secondary multiplication surface, fill or pressurize guides) 6. Investigating systems for power beam safety and wrote a paper on Space Policy Issues of SSP WPT beams. 7. Provided estimates of areal mass density, specific power, system element efficiencies, voltages, operating temperatures, etc. to the SSP System Study Group. Inputted pointing errors, required surface errors, subarray sizes, etc. to the Structures Group. Operating voltages, currents and regulation required to the PMAD Group. Land area required and biota interactions to the Environmental Group. Assembly, maintenance and phase calibration interface data supplied to the Robotics Group. 8. Identified key problems in the RF-Spectrum-EMC, thermal, and grating-lobe control areas, in addition to RF-breakdown. State of the art (SOA), but applicable quantitative numbers and examples ( mostly Raytheon, ground-based) are given below with corresponding SSP in-space requirements for comparison of the required technology challenges .

25. 5.8 GHz GEO WIRELESS POWER TRANSMISSION SYSTEM DESIGN EXAMPLE DC Power Distribution DC-RF Power Conversion Efficiency Waste Heat Removal Source PMAD Subarray Aperture Efficiency Subarray Failures Amplitude Errors & Taper Quantization Phase Errors Electronic Beam Steering Scan Loss Transmitter Monitor & Control System BEAM SAFETY SUBSYSTEM Beam Coupling Efficiency Propagation Impairments Polarization Mismatch Rectenna Aperture Scan Loss Rectenna Aperture Efficiency Rectenna RF-DC Power Conversion Efficiency Waste Heat Removal DC Power Collection Load PMAD Rectenna Monitor & Control System D t = 500m D r = 7500 m  m  km   b = 0.9182 Edge Taper = -10.02 dB Peak/Ave P.D. = 2.35 Clear Air = -0.05 dB = 0.9885 4mm/hr Rain @ 0.01 dB/km X 2.5 km = -0.025 dB = 0.994 0.90 -0.458 dB 0.95 -0.706 dB 0.96 2% Random Failures 0.986 10-Step & +/- 1 dB 0. 97 10 deg rms 0..977 -0.1 dB max 0.933 0.918 0.999 +/- 2 deg 0.999 -0.0 dB max 0.95 0.86 EMC & Diplexing Filters 0.794 -1 dB EMC Filtering 0.891 -0.5 dB Rectenna Element Failures 0.99 -1% 0.395 Overall WPT Efficiency RADIATE RECEIVE PROPAGATE WPT SYSTEM PARAMETERS

26. 5.8 GHz Magnetron Directional Amplifier (MDA) SSP Subarrays* Richard M. Dickinson, JPL 4m X 4m Edge Subarray 3 X 3 = 9-MDAs Yielding ~ 2.8 kW/m 2 PFD and thus -9.5 dB Aperture Taper Portion of 4m X 4m Central Subarray with 9 X 9 = 81-MDAs Yielding ~ 25 kW/m 2 PFD for 1.2 GWe System Slotted Waveguide Transmitting Antenna ~ 6 kg/m2, 0.5 mm (.02’) Aluminum (~ 1100slots/m 2 ) ~ 3.2 cm thick (Cross Feeds + Radiating Waveguides) * Var. of Brown, W. C.,”Satellite Power System (SPS) Magnetron Tube Assessment Study, “ NASA Contract NAS-8-33157, for MSFC, 7/10/80. Two Central Devices Diplexed for Retrodirective Pilot Beam Receiver Function MLI Blankets Over 95 deg C Electronics Peak Mass Density = Transmitter@ 5.7 kg/m 2 Antenna @ 6 kg/m 2 Absorptive & Reflective Filters @ 2 kg/m 2 HVDC Distribution Lines@0.263 kg/m 2 TOTAL RF Peak Density = 14 kg/m 2 Edge Subarray Density = 7.7 kg/m 2 Total “Average” Mass Density ~ 32 kg/m2 NOTE: Not To Scale Est. PMAD@1.5kg/kW ~20kg/m 2 5 kW RF out, 85.5% efficient Magnetron, ~1kg, 6 kV, 1A & 70 W, 5s-Starting Filament & Off 44 cm dia., 350 deg C Pyrolytic Graphite Radiator Dumping 850W Waveguide Phase-Reference, Circulator, Filters, ASIC- MMIC, Buck-Boost Coil, Guide- Tuner and Power Distribution

27. SSP Wireless Power Transmission Technology-I 1 . SOA DC-RF Conversion -%/W/ GHz /C .76/6.9/ 8.0 /125 .83/900/ 2.45 /135 .75/50kW/ 2.45 /100 SSP Required = .90/6-60/ 5.8 /300 .855/6kW/ 5.8 /350 .83/26kW /5.8 /500 2 . SOA Large Phased Arrays (non Retrodirective) PAVE PAWS@UHF Cobra Dane@L-Band THAAD ~2mX5m, 25,344 X-Band Elements 31m dia(twin)-3/4MW 29m dia-1MW(TWTs) TRW- Capistrano HPM 48-6ft S-Band Dishes 1,792 active elements of 5354 15,3600 elements SSP @5.8GHz, 500m dia, ~2 GW CW out, #elements= 83,841,253 381,618 82,589 3 . 2.45 EMC dBc/Hz@50MHz & 2ndHarmonic= -150 & -40dBc -190 & -60dBc -160 & -30dBc SSP EMC Requirement @ 5.8 GHz+/- 75 MHz & Fleet of ~ 100 SSP in View= -174dBW/m 2 /Hz? 4 . SOA Spacecraft Filter Multipacting Breakdown Margin= 6-10dB at C & Ku-Band 10-50W, 13 yrs. SSP @ 5.8GHz Margin Requirement >6 dB for 40 years= 60W 6 kW 26kW Solid State Magnetron Klystron Phase Injection Locked Richard M. Dickinson, JPL

28. SSP Wireless Power Transmission Technology-II 5 . SOA CW Microwave Power $/W, GHz, Quan.= $3, 1.9,100s $.025,2.45,100Ks $1.25,UHF,2s SSP Required CW Microwave Power at 5.8 GHz, Fleet of 100 Quantity = $1-2/W, 10 5 -10 9 6 . SOA Microwave Device, Thermal & PMAD kW/kg= .01 .2 .02 SSP WPT Array System Specific Power (kW/kg) .42 .34 .3 Key Technology Item s GaN@300C PLL-ASIC 5-Stage MDC@500C Solid State Magnetron Klystron Phase Injection Locked The near term technology to be developed is the ASIC/MMIC for using modified cooker tube magnetrons as phased array sources for retrodirective power transmitting phased arrays in beaming power to station keep geostationary stratospheric platforms for telecommunication and scientific observation applications. ( ~ $ 1-2M/ 1 yr) 50-100V 3.5-6kV 28kV ASIC=Applicaion Specific Integrated Circuit GaN=Gallium Nitride MDC=Multiple Depressed Collector PLL=Phase Locked Loop PMAD=Power Management & Distribution dBc=Decibels Below the Carrier Level dBW=Decibels Relative to a Watt Richard M. Dickinson, JPL

29. SSP Wireless Power Transmission Technology-III To Lower the Barriers to SSP, Technology is Needed to Permit: 1. Electromagnetic Compatibility (EMC) - A . Power Beam Frequency Allocation at wavelengths with less than 5% (0.2 dB) atmosphere propagation impairment for 99.5% of a year. Bandwidth at auction for less than $100/Hz? WPT Service definition in the International Telecommunicaton Union (ITU) by over 50% of the 182 member countries. B. Close-In Carrier Noise and Harmonic Filtering in GEO, with less than 10% (0.5 dB) insertion loss and greater than a safety factor of 2 (Voltage ratio, 6 dB Power) multipacting breakdown margin for less than 2 kg/m 2 areal density. Less than 15% (0.7 dB) insertion loss for ground based rectennas at less than $0.2/W. 2. Lifetime - 40 year lifetime for high power microwave devices and parts in GEO. 3. Beam Safety Perception - The “fear of frying” must be overcome by working demos and public education of beam safety marking and intrusion detection with safe beam interruption and restoration, for less than $.005/kWh delivered energy. Richard M. Dickinson, JPL

30. Bill Brown’s* M agnetron D irectional A mplifier Using A Modified Cooker Tube Amplitude Comparator- Driver Buck-Boost Coil Modified Cooker Magnetron Waveguide Reactance Tuner Ferrite Circulator Directional Couplers To Antenna Phase Comparator RF Driver Amplifier 5- Bit Phase Shifter Phaser Driver Phaser Commands Power Output Ref. 2.45 GHz Ref. Signal React- ance Driver WCB MDA MMIC-ASIC (TBD) Power Converter Supply Voltage * Brown, William C.,”Development of Electronically Steerable Phased Array Module (ESPAM) with Magnetron Directional Amplifier (MDA) Power Source,” Final Report, Microwave Power Transmission Systems, Weston MA, Texas A&M Research Foundation Subgrant No. L300060, Project RF-2500-95, Sept. 1995. ** McDowell, Hunter L.,”Magnetron Simulation Using a Moving Wavelength Computer Code,”IEEE Trans. Plasma Science, Vol. 26, No. 3, pp.733-754, June 1998. 300-1000 W 3.35-3.85 kV ~ 300mA ~ 1 W -20dB ~ 30 dB Gain -50 dB Notes: By not powering the magnetron, the low power level RF driver signal can be reflected through the circulator to the antenna, yielding a two-level unit. Filament turned off after start for clean spectrum**. ~ 2-3 W ~10 mW ~ 1/3500 V/W 0.0024 H, 8.6 Ohms ~ 75% Efficient ASIC/MMIC Needs Developing Richard M. Dickinson, JPL

31. Slotted Waveguide Subarray Low Cost Manufacture (With Built In Filtering and Multipaction Inhibiting) Concept by Bill Brown[1] Punch Registration Cut Tab Relief Bend Tab Form Inter- W/G Wall Punch Radiating Waveguide Slots Form End Walls Heavy Reynolds Wrap or Equiv. Aluminum Sheet Stock Integrate Halves & Spot Weld Assy. Add Feed Guide-Filter to Assy. with Magnetron Flange 1. Brown, W. C.,”Microwave Beamed Power Technology Development,” Final Report JPL Contract No. 955104, Raytheon PT-5613, May 15, 1980. Punch Registration 8-Slot X 8-Stick W/G Subarray (front view) W/G TOOLING NEEDS TO BE DEVELOPED! (back view) Dielectric Cladding Richard M. Dickinson, JPL ..... ..... ..... ..... ..... .....

32. WIRELESS POWER TRANSMISSION NEEDS I. In order to obtain a service definition and frequency allocation for SSP use, it will be necessary to show the ITU that the SSP can be designed and maintained Electromagnetically Compatible with other users of the Radio Spectrum. II. Because of the GW power levels and the rain of electromagnetic energy falling to Earth from a fleet of SSP spacecraft functioning under various operational and environmental conditions, it is required to filter the carrier noise outside the ISM band, to filter the harmonics, to provide notch filters on the spacecraft and possibly on ground radio and radar equipment functioning at certain sensitive frequencies outside the ISM bands. III. There still exist large uncertainties in the WPT performance and the cost impacts due to the lack of analysis, measurements, models and victim susceptibility data for determining the SSP Electromagnetic Compatibility (EMC) requirements . IV. Furthermore, a functioning WPT facility does not now exist to validate the adequacy of mitigation approaches or the costs both economically and in filters insertion loss required to achieve EMC both on the transmitters and on the rectennas. V. Will careful engineering design be economically affordable and adequate to prevent serious interference to other users of the electromagnetic Spectrum? Richard M. Dickinson, JPL

36. TRL Status of Advanced Solar Cell/Arrays MRO Rigid Panel Array (60 W/kg) TJ Cells ( 27% eff) TRL 8-9 NM ST-8 Ultraflex Array ( 180 Wh/kg) TJ Cells ( 28% eff) TRL 5 Quantum dot Solar Cells Eff (> 40%) TRL 1-2 Four Junction solar Cells Eff (> 35 %) Experimental .Cells TRL 2-3 TJ Cells ( 27% eff) In production TRL4 Phoenix Ultraflex Array ( 100 Wh/kg) TJ Cells ( 27% eff) TRL 6-7

37. www.aec-able.com Tel: 805.685.2262 Fax: 805.685.1369 Able Engineering Company Corporate Headquarters, 7200 Hollister Ave., Goleta, CA 93117 Advanced Array Designs FTFPV Solar Array UltraFlex CellSaver SquareRigger

39. Challenges to Traditional Approach for Autonomy and Robotics • Competitive pressures are moving robotic manufacturing and assembly toward shorter product cycles, lower inventories, higher equipment utilization, and shorter lead times, as a result scheduling and control gained priority. • Scheduling and control has been a process of command and response that relies heavily on hierarchical models. • Centralization leads to complexity: The control software must handle the entire system and anticipate every circumstance than can arise. Changes in the configuration of the system require changes in the control software. The central computer and database are a bottleneck that can limit the capacity of the performance , and constitute a single point failure that can bring down the entire facility. • Hierarchy also leads to complexity: Hierarchical control schemes bind workstations into groupings that are difficult to change as the system operates. The hierarchical rule of information flow through supervisors means that naturally occurring lateral information flows are often duplicated, leading to needless redundancy and the possibility of inconsistency between the two versions N. Marzwell

47. DoD, National, and International Impact Proposed Vision & Objectives of Space Solar Power Assured U.S. Preeminence in Space Access and Operations through Dramatic Advances in Transformational Space Capabilities Innovation that Creates Novel Technologies and Systems Enabling New, Highly Profitable Industries on Earth and in Space Assured Energy Security for the U.S. and Its Allies through Affordable & Abundant Space Solar Power with First Power within 25 years - VISION - The United States and Partners enable – within the next 20 years – the development and deployment of affordable Space Solar Power systems that assure the long-term, sustainable energy security of the U.S. and all mankind