Boechler nicholas[1]

Direct Conversion for
Space Solar Power
Nicholas Boechler
gtg218s@mail.gatech.edu
Research Advisor: Prof. Komerath

Direct Conversion Concept
Given broad/narrow band EM radiation
source
„„ Sun
„„ Man made EM transmission
„„ Other bodies: Jupiter, albedo from the Moon
Absorb radiation and convert directly to
lower narrowband frequency for re re-emission
Benefits:
„„ Increased efficiency
„„ Lower mass
„„ Increased simplicity

Project Goals
Study a number of options that might lead to direct
conversion
Analyze technology that would warrant further
exploration:
-Aerospace systems applications?
-Possible mass per unit power?
Provide a justifiable estimate of mass per unit
power of future direct conversion systems
Identify possible future applications that would
benefit from direct conversion technology.

Current Technological Road Blocks
to Space Solar Power Systems (1)
Photovoltaic Technology
„„ Old technology w/ low efficiency
„„ Band gap
„„ Direct current only –– must re re-oscillate
„„ Relatively low specific power
Solar Cell Performance
Thick Film
Thin Film
Efficiency
25-40%
10-20%
Specific Power (kW/kg)
.05-.25
.05-.25
Power Density (kW/m^2)
.1-.4
.1-.4
Solar Cell Performance [1,2,3,4,5]. Note: high estimate taken, usually not that good and decays w/ time.

Current Technological Road Blocks
to Space Solar Power Systems (2)
High Launch Costs
„„ Importance of specific power
Booster
2004 Cost ($ millions)
Payload to LEO (kg)
Payload Cost ($/kg)
Atlas 5 551
125.1
20,050
6239.4
Delta 4 Heavy
193.4
25,800
7496.12
Space Shuttle
284
24,400
11639.3
Titan 4B
491.6
21,680
22675.3
Robel, M. [6]

Initial Direct Conversion Options
Shocked Photonic Crystals [Joannopoulos 7,8,9]
Signal Processing Solutions
Optical Resonators [Iltchenko 10 10]
Rapidly Ionizing Plasma [Ren 11]
Solar Pumped Lasers and Masers [12,13]
Optical Rectennae [14,15]
Nanofabricated Antennae

Discounted Options (1)
Signal Processing Solutions
„„ Inefficient and some require a significant additional
power source
„„ Tube, Cyclotron, Gyrotron type devices
Mechanical tolerances
Scaling problems
More difficult at higher frequencies
Low efficiency that degrades over time
Heavy
Impedance mismatching
Breakdown fields
Have not found any efficiencies over 60% and few near it

Optical Resonator
„„ Converts to amplified narrowband but does so
inefficiently by rejecting non non-resonant
wavelengths
Rapidly Ionizing Plasma [Ren 11] and
Nanofabricated Antenna
„„ Difficulty further developing viable concept

Optical Rectenna [1,2]
„„ Based of previous work of ITN Energy Systems
and W.C. Brown
„„ Still very applicable technology, however it is
surpassed by the possibility of focusing
broadband radiation directly onto a medium
Estimated Efficiency = 85 85-100%:
Power Density = 1.165 kW/m^2 [W.C. Brown Microwave
Rectenna Weight = .25 kg/m^2 [3]
Specific Power = 4.658 kW/kg
1763% Increase in Specific Power over photovoltaics

Refined System Concepts
Near Term Concept
„„ Solar Pumped Maser
Long Term Concept
„„ Shocked Photonic Crystals

MASERs
MASER= Microwave icrowave Amplification by
mplification Stimulated timulated Emission of mission Radiation adiation
Naturally Occurring
„„ Detection of 183 GHz water vapor maser
emission from interstellar and circumstellar
sources [16]
Rotational transition of H2O
„„ 145 GHz Methanol maser
Collision excited [17]

Earth Atmosphere AbsorptionEarth Absorptionhttp://www.islandone.org/LEOBiblio/microwave_transm.gif

MASER/LASER Examples
Saiki, T. “Development of Solar-Pumped Lasers for Space Solar Power Station” [18]
„„ Solar pumped Nd/Cr:YAGceramic laser
„„ Demonstrated 38% efficiency
Kiss, Z. J. “Sun Pumped Continuous Optical
Maser” [19]
„„ 1963
„„ Shows same principle of solar pumped lasers can be
applied to lower more convenient frequencies

Argument for Efficiency
Use low density molecular vapor as in naturally
occurring masers
„„ Analogous to lasers
Maser uses rotation rotation-vibration transitions on the
molecular level
„„ Laser uses optical optical-electronic transitions on the
subatomic level
„„ 38% with a laser already proven –– should be able to
do better.
„„ DARPA aiming for 50% with 1W CW laser
Longer wavelengths –– everything scaled up and
easier to control

Parabolic Reflector
Solar sail type material for reflector
„„ 1-10 g/m^2 [20]
„„ May be heavier to prevent scatter –– but will
still be significantly lighter than traditional
options

Problems/Considerations
Gas would have to be kept at uniform temperature
for maximum efficiency
„„ Balance between heating of radiation and cooling to the
vacuum
„„ Solar weather
Unpredictability due to low density and possible
high temperature
Possible band gap –– ie ie: portions of band perhaps
: ineffective towards transition
Scattering/surface losses

Photonic Crystals
Through artificial
geometry can create
perfect waveguides and
resonant cavities
High to perfect
theoretical efficiencies
[Joannopoulos7,8,9]

Shocked Photonic Crystals (2)
Doppler Shift and Photonic Crystals
„„ 2003 MIT
„„ Discovered that a non non-relativistic reversed
Doppler Shift in light occurs when light is
reflected from a moving shock wave
propagating through a photonic crystal
„„ Near 100% efficiency
„„ Proposed that a similar system be used in
micro micro-electrical electrical-mechanical devices. [7,8]

Simulation of frequency shift in photonic crystals from JoannopoulosJ. [8]

Shocked Photonic Crystal System
Solar sail type parabolic reflector
“Shock like” modulation of the dielectric
with separate power source
Serially placed photonic crystals or single
crystal with gradient geometry
„„ Possible mismatch to geometry with large
frequency shift over the course of the crystal
Resulting pulsed transmission

Shocked Photonic Crystal System

Problems/Considerations
Creating a shock
„„ Physical shock too much energy
„„ “Shock like” modulation of the dielectric –– still energy loss, but
perhaps smaller
Need more information
Has not been physically tested –– only simulations
„„ Initial efficiency probably low
„„ Depends greatly on nanotechnology
„„ Would have to limit unexpected internal scattering
Surface interface reflection and scattering still a problem
Heat over time

Shocked Photonic Crystal
Calculations (1)

Shocked Photonic Crystal
Calculations (2)

Applications (1)
Space Solar Power Grid
Improved Efficiency: Based on calculations by
Kulcinski [21], assuming a change of conversion
efficiency from 15.7%, and 76.6% efficiency loss due to
DC to RF conversion (don don’’t know where he got that
number –– should be lower)
„„ Overall system efficiency from 7.81% to 64.9%
Distribution System: no DC conversion
between satellites

Applications (2)
Electric Propulsion:
Problems: High mass per
unit thrust, due to the power
source and transmission
system.
Potential Systems:
„„ Ion Engines: Ionize
propellant particles such
as xenon gas by EM
radiation and accelerate
them through an electric
field.
Ion Engine from ESA

Applications (3)
MagnetoplasmaMagnetoplasmaEngines and Engines MagMagBeamBeam: Heating : neutral hydrogen gas into plasma using electric fields and contained by magnetic fields, the plasma then passes through an RF booster to further ionize the hydrogen plasma [22,23]Solar Sail Hybrid Systems: Solar sails are combined with electric propulsion systems to function as a both a solar sail and reflector to power the electric propulsion system [24].Magbeamfrom Winglee, R. [23]

Hybrid system from Landis, G. [24]

Applications (4)
Benefits from Direct Conversion:
More Available Energy
„„ More energy can be gathered more
efficiently
„„ Eliminate the need for an onboard power
system
„„ Direct Conversion to Ionization Frequency
„„ Ultra Thin Solar Sail Possibilities
Hybrid

Future
Refine Estimates
Information Needed
„„ Flux and Power capacities of molecular
vapors and crystal systems
„„ Temperature and density target for maser
„„ How fast heat can transfer through the
various mediums –– determines geometry
„„ Capacity of solar sail reflectors
„„ Shock like modulation of the dielectric

Bibliography
[1] U.S. Department of Energy, “BandgapEnergies of Semiconductors and Light”. Feb2004. http://www.eere.energy.gov/solar/bandgap_energies.html[2] Murphy, D. M., Ekanazi, M.I., White, S.F., Spence, B.R., “Thin-Film andCrystalline Solar Cell Array System Performance Comparisons”. AEC-Able (ABLE) Engineering. [3] Tuttle, J.R., SzalajA., Keane J., “A 15.2% AM0 / 1433 W/KG THIN-FILMCU(IN,GA)SE2 SOLAR CELL FOR SPACE APPLICATIONS”. 28th IEEEPhotovoltaicsSpecialists Conference, Anchorage, AK September 15-22, 2000[4] Kellum, M., Laubscher, B., “Solar Power Satellite Systems With a Space Elevator”. LAUR-04-4073. 3rd Annual International Space Elevator Conference, Washington, D.C., 29 June2004. [5] National Center for Photovoltaics. “PhotovoltaicsNew Energy for the NewMillenium”. www.nrel.gov/ncpv. [6] Robel, Michael K. “The cost of medium lift”. The Space Review. June 1, 2004. http://www.thespacereview.com/article/150/1[7] Joannopoulos, John D., Reed, E., Soljacic, M., “Color of Shock Waves in PhotonicCrystals”. Physical Review Letters. 23 May 2003. [8] Joannopoulos, John D., Reed, E., Soljacic, M., “Reversed Doppler Effect inPhotonic Crystals”. Physical Review Letters. Sept 2003. [9] Joannopoulos, John D., Johnson, Steven G., “Photonic Cystals: The Road from Theory to Practice.” Massachusetts Institute of Technology. 2002. [10] Iltchenko, V., Matsko, A., Savchenkov, A., Maleki, L., “A Resonator for Low- Threshold Frequency Conversion”. JPL. http://www.nasatech.com/Briefs/Dec04/NPO30638.html[11] Ren, A., Kuo, S.P., “Frequency Downshift in Rapidly Ionizing Media”. 1994. [12] Kiss, Z. J., Lewis, H. R., Duncan, R. C. Jr., “Sun Pumped Continuous Optical Maser”. Applied Physics Letters. March 1963. [13] Saiki, T., Uchida, S., Motokoshi, S., Imasaki, K., Nakatsuka, M., Nagayama, H., Saito, Y., Niino, M., Mori, M., “Development of Solar-Pumped Lasers for Space Solar Power Station”. Space Technology Applications International Forum. October 2005. [14] Brown, W.C., “The History of Power Transmission By Radio Waves”. IEEETrans.Vol. MTT-32, p:1230 (1984). [15] Berland, B., “PhotoVoltaicTechnologies Beyond the Horizon: Optical RectennaSolar Cell”. Final Report, NREL/SR-520-33263, February 2003. [16] Cernicharo, J., Thum, C., Hein,H., John,D., Garcia,P.; Mattioco,F. “Detection of 183 GHz water vapor maser emission from interstellar and circumstellarsources.” Astronomy and Astrophysics (ISSN 0004-6361), vol. 231, no. 2, May 1990, p. L15-L18. [17] “New Methanol Maser.” IRAM Annual Report 1989. http://iram.fr/IRAMFR/ARN/AnnualReports/1989/1989_15.pdf[18] Saiki, T., Uchida, S., Motokoshi, S., Imasaki, K., Nakatsuka, M., Nagayama, H., Saito, Y., Niino, M., Mori, M., “Development of Solar-Pumped Lasers for Space Solar Power Station”. Space Technology Applications International Forum. October 2005. [19] Kiss, Z. J., Lewis, H. R., Duncan, R. C. Jr., “Sun Pumped Continuous Optical Maser”. Applied Physics Letters. March 1963. [20] “Solar Sail Technology Development: Mission Senarios” JPL. Mar 2002. http://solarsails.jpl.nasa.gov/introduction/mission-scenarios.html[21] Kulcinski, G.L., “Solar Energy Resources –Orbiting Solar Power Satellites” Lecture 34. National Research Council. Nov 2001. [22] NASA's Human Exploration and Development of Space Enterprise, “Propulsion Systems of the Future”. 15 May 2003. http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html[23] Winglee, R., “Magnetized Beamed Plasma Propulsion (MagBeam).” NIAC. March 2005. [24] Landis, Geoffrey A., “Optics and Materials Considerationsfor a Laser-propelled Lightsail”. Paper IAA-89-664 at the 40th International AstronauticalFederation Congress, Málaga, Spain, Oct. 7-12, 1989. Revised December, 1989.

Thanks!
Research Advisor & Mentor: Dr. Komerath
„„ Additional guidance on lasers/masers, photonic
crystals, and other questions
Dr. Citrin (GT)
Dr. Kenney (GT)
Dr. Joannopoulos (MIT)
Dr. Marzwell (JPL)
Dr. Olds (GT & SpaceWorks Engineering Inc.)
Dr. Reed (Lawrence Livermore National Lab)
NASA Institute for Advanced Concepts

Boechler nicholas[1]

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