The Case for Millimeter Wave Power Beaming

1
The Case for Millimeter Wave Power Beaming
Narayanan Komerath Daniel Guggenheim School of
Aerospace Engineering Georgia Institute of
Technology Atlanta
IMETI 2011, Orlando, FL June 2011
2
Millimeter waves are used primarily for imaging
and short-range signal transmission. One cited
advantage is that many frequencies in this range
get attenuated within a short range, minimizing
interference between devices. Others propagate
very well.
Power beaming will enable breakthroughs in power
delivery to and from off-grid areas. Synergy
between terrestrial and space-based power
generation Eventual progression to space solar
power. Arguments against using millimeter waves
are reviewed and compared against the
implications of recent developments. 100 GHz
suitable for terrestrial short-range
beaming, 220GHz suitable for transmission via
stratospheric platforms and space. Advances in
optical heterodyning, evaporation ducts,
absorption by atmospheric water, oxygen and
nitrogen, and synergy with photovoltaic and
mobile telecommunications infrastructure are
relevant to bringing about millimeter wave power
beaming solutions.
3
Conclusions To Date In this paper, the reasons
for millimeter wave power beaming are considered,
along with the associated problems, and avenues
for their possible solution. 1. Millimeter wave
beaming is essential to success in bringing Space
Solar Power to earth, because it brings antenna
and transmitter sizes down to sizes practical for
retail installation and perhaps even portable
emergency installations. 2. It enables retail
distribution of power to off-grid locations and
islands. 3. It enables synergy with distributed
micro renewable power architectures. 4. Technical
options for building millimeter wave generators,
transmitters and receivers are improving rapidly
towards mass production 5. Synergy with
photovoltaic arrays is feasible and promises
substantial improvements in the
cost-effectiveness of micro power architectures.
6. Concerns about atmospheric absorption and
scattering remain to be resolved, but there are
interesting options to pursue. 7. Optimal
choices for propagation through moist atmospheres
and for long-distance dry air and vacuum beaming
differ. 8. Solid-state arrays promise the
option of using several beam frequencies from the
same arrays in order to serve multiple purposes.
9. The possibility of evaporation ducts for
atmospheric propagation should be explored.
10. The optimal architecture appears to consist
of a 2000km constellation of 96 power grid
satellites performing intercontinental power
exchanges, and a network of stratospheric
platforms for local and regional exchanges and
retail distribution to customers.
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The reasons in favor of considering millimeter
wave beaming from lower orbits are summarized
below 1. Reduction in antenna area by 2 orders
of magnitude compared to the 2.45-5GHz
regime. 2. Unlike the 1960s, when the antenna had
to be aimed mechanically, unlike the Phased Array
beam steering technology of today. 3. The
substantial problems of accurate pointing over
large distances have been solved in the beam
weapons community and the space program. In
addition, adaptive control can iteratively refine
the beaming accuracy before full-power operation.
Today smart antennae use Digital Signal
Processing (DSP) to identify moving cellphone
locations in real time to minimize cross-talk
21. 4. The fears about misdirected death rays
are misplaced. The full beam operates only when a
trigger link is operating. 5. The above
considerations make it possible to consider
beaming from Low or Mid Earth Orbit (L/MEO),
about 2000 kilometers high, rather than the 36000
kilometers from GEO. This further reduces antenna
size. 6. With L/MEO satellites, transient
passage over any ground station, and several
space-to-space passes to reach different places
on Earth are issues. Space-space power exchange
is also needed for any scaled-up SSP system.
7. In the 1960s, millimeter wave power was
generated using vacuum tubes and gyratrons, at a
very high cost in mass per unit power, and severe
maintenance demands. Today this situation has
improved dramatically, with very large arrays of
mass-produced solid-state devices 22. These
devices also achieve higher conversion
efficiencies from DC or AC to millimeter waves,
so that the heat dissipation problem is reduced
substantially. 8. Frequency selection was a
difficult issue with vacuum tubes. Today, with
solid state devices, digital signal processing
(DSP) and phase-locked loop (PLL) technology
enable quick changes and accurate choices to
narrow frequency bands. Conceivably, the same
array could operate at more than one frequency,
or at multiple frequencies intermeshed. This has
many implications. There are large issues, for
instance whether this works when the purpose is
power conversion rather than generating a
small-amplitude signal. 9. One of the most
interesting features of beaming from a low orbit
constellation is that power can reach every point
on Earths surface, unlike GEO-based craft which
would be too low on the horizon at high
latitudes. This can be done without massive
terrestrial wired grids. Hence it makes sense to
use frequencies that enable the location of small
receivers in remote places and on islands that
are inaccessible to the wired grids. 10. With a
wireless power infrastructure, one can consider
integrating a huge number of standalone power
generating devices into a wireless grid. This
opens up the possibilities for micro renewable
power generators worldwide. 11. Automotive radar
at 77 and 79 GHz, and some quasi-weapons in the
80-94GHz range are examples, the latter of
higher-power applications.
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Figure 3 Transmission through a dry atmosphere
(less than 50mm precipitable moisture).
Astronomical observatory data, Mauna Kea, Hawaii.
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Issues And Solutions
Expense of solid state arrays vs. PV arrays
12
2. Atmospheric Propagation Losses
13
3. High Beam Intensity
14
4. Health Effects of Millimeter Waves
15
4. Generation of Millimeter Waves
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The reasons in favor of considering millimeter
wave beaming from lower orbits are summarized
below 1. Reduction in antenna area by 2 orders
of magnitude compared to the 2.45-5GHz
regime. 2. Unlike the 1960s, when the antenna had
to be aimed mechanically, unlike the Phased Array
beam steering technology of today. 3. The
substantial problems of accurate pointing over
large distances have been solved in the beam
weapons community and the space program. In
addition, adaptive control can iteratively refine
the beaming accuracy before full-power operation.
Today smart antennae use Digital Signal
Processing (DSP) to identify moving cellphone
locations in real time to minimize cross-talk
21. 4. The fears about misdirected death rays
are misplaced. The full beam operates only when a
trigger link is operating. 5. The above
considerations make it possible to consider
beaming from Low or Mid Earth Orbit (L/MEO),
about 2000 kilometers high, rather than the 36000
kilometers from GEO. This further reduces antenna
size. 6. With L/MEO satellites, transient
passage over any ground station, and several
space-to-space passes to reach different places
on Earth are issues. Space-space power exchange
is also needed for any scaled-up SSP system.
7. In the 1960s, millimeter wave power was
generated using vacuum tubes and gyratrons, at a
very high cost in mass per unit power, and severe
maintenance demands. Today this situation has
improved dramatically, with very large arrays of
mass-produced solid-state devices 22. These
devices also achieve higher conversion
efficiencies from DC or AC to millimeter waves,
so that the heat dissipation problem is reduced
substantially. 8. Frequency selection was a
difficult issue with vacuum tubes. Today, with
solid state devices, digital signal processing
(DSP) and phase-locked loop (PLL) technology
enable quick changes and accurate choices to
narrow frequency bands. Conceivably, the same
array could operate at more than one frequency,
or at multiple frequencies intermeshed. This has
many implications. There are large issues, for
instance whether this works when the purpose is
power conversion rather than generating a
small-amplitude signal. 9. One of the most
interesting features of beaming from a low orbit
constellation is that power can reach every point
on Earths surface, unlike GEO-based craft which
would be too low on the horizon at high
latitudes. This can be done without massive
terrestrial wired grids. Hence it makes sense to
use frequencies that enable the location of small
receivers in remote places and on islands that
are inaccessible to the wired grids. 10. With a
wireless power infrastructure, one can consider
integrating a huge number of standalone power
generating devices into a wireless grid. This
opens up the possibilities for micro renewable
power generators worldwide. 11. Automotive radar
at 77 and 79 GHz, and some quasi-weapons in the
80-94GHz range are examples, the latter of
higher-power applications.
19
ACKNOWLEDGEMENTS
The work reported in this paper was made possible
by resources being developed for the EXTROVERT
cross-disciplinary learning project under NASA
Grant NNX09AF67G S01. Mr. Anthony Springer is the
Technical Monitor.
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Beamed Retail Power Transmission/ Distribution
System

• Wireless transmission of power (not just signals
  with information) over relatively short
  distances to multiple end-user receivers.
• Usually implies focused point-to-point
  transmission with highly directional antennae,
  and provisions for energy storage at either end.
  
• Conventional solutions using lt10GHz microwave,
  and some proposed solutions using lasers.
• Our interest is in the millimeter wave regime,
  specifically near 220 GHz

21
Market Indicator For Micro-Scale Retail Power
Malawian teenager .. transformed his village by
building electric windmills out of junk Jude
Sheerin, BBC News 1 October 2009 http//news.bbc.c
o.uk/2/hi/africa/8257153.stm

• Notes
• Original motivation power a radio to fance to
  music
• Business plan charging station for cellphones.
• Lesson Demand for cellphones and other
  electronic systems is far ahead of
• national Power Grid expansion rate.

22
Introduction
Beaming power may be a viable alternative to
constructing wire grids for several future
applications, despite low efficiency. Route for
the small electronic devices market to leapfrog
the centralized power grid, in many parts of the
world. This paper looks at the rationale,
applications, choices and tradeoffs.
23
Overview

• Long-term rationale why we are interested
• Near-term applications
• Technical barriers
• Cost tradeoffs
• Possible innovations needed

24
Aerospace Interest Stratospheric/ Space Power
Grid

• Way to exchange power between day/night regions
  to boost solar power baseload capability
• Minimize storage needed to capture wind power
  spikes
• Provide evolutionary path to space solar power
• Retail power beaming is the end-user
  infrastructure for delivery of power in a global
  exchange, including space solar power.

25
Why SSP? Why has it Remained a Dream?
Feature SSP Ground-based solar power
Steady generation 24 hour, year-round. 12,000KWh/m2 per yr Daily /seasonal/ weather fluctuations. Average 900 to 2,300 KWh/yr
Waste heat Dissipated in Space Released on Earth
Transmission efficiency Low, weather-dependent High, independent of weather (see above)
Receiver/distributor Infrastructure size Massive for GEO sats due to beam width, for any power level Scalable from rooftop to Sahara size
Generator size Massive for GEO sats. Scalable
Installation cost per watt Very high due to GEO launch cost Moderate
26
The Space Power Grid Approach

• Use space-based infrastructure to boost
  terrestrial green energy production from land
  and sea argument for public support.
• Full Space Solar Power (very large collectors in
  high orbit) will add gradually to
  revenue-generating infrastructure.

• Exploit large geographical, daily and seasonal
  fluctuations in power cost.
• Beam to other satellites.
• Retail delivery (SPS2000).

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Afternoon Sun system.

• 80 minutes of access per 24 hours per location.
• This orbit performs 23 revolutions around the
  earth every 48 hours.

Ground Tracks of 6 sun-synchronous satellites at
1900 km
28
Near-term Rationale Wired vs. Beamed Power
Transfer
Wire Grid Beamed Power
Excellent efficiency with high voltage lines (94) Requires large transmission infrastructure. Large amount of developed land, trees cleared etc Remote area maintenance Power line hazards under and near lines high voltage, aircraft collision, ice and wind storm issues Vandalism and terror attacks High cost as number of receiving points increases Low efficiency (20 to 50) Few transmission and reception points Clear line of sight, can be above tree level Concentrated at points Radiation hazard along the beam Less susceptible Each device has to have a converter
29
Potential Near-Term Applications

• Broad area low intensity power distribution for
  emergencies
• Areas with cellphones/ players but no power grid
• Rapid power delivery to remote military or
  scientific outposts
• High endurance miniature robots
• Distributed micro power generation
• Remote area exploration
• Increased range for electrically powered vehicles
  
• Rapid restructuring of grid topology for damage
  mitigation

30
Technical Issues

• Antenna size vs. distance relationship means that
  space grid system is not viable at any power
  cost, without going to millimeter wave regime,
  above 100 GHz
• Atmospheric transmission window at 220 GHz seems
  ideal
• Anything above 10 GHz is extremely sensitive to
  rain finding alternative routes is the answer.
• Poor conversion efficiency from DC to mm wave

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Feasibility of low range low efficiency BPTS
Modified Friis equation calculation shows that
antenna combination of (20m 5m) is adequate
for 100km range at 200 GHz. (20m1m) is good for
10 km
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MM waves offer high free-space efficiency
20m transmitter diameter, 5m receiver diameter
Power Efficiency, Pr/Pt
Frequency in GHz
33
Cost Model, Wired vs. Retail Beamed Power
Infrastructure
Wired installation Effective cost per km (
US1M / km) linear with distance above a
threshold level, steep cost for last few kms of
retail distribution.
BPTS power loss proportional to square of
(distance/frequency). Effective cost US100K/km
(1 transmitter/ relay per km)
34
Cost-effectiveness of BPTS vs. Wired Grid
Installation
Effective Installation Cost in K
Even at 20 GHz, BPTS is more cost effective than
wired installation for distance less than 6 km
Range in km
35
Required Technological Innovations

• Efficient mm Wave Generation
• Thyratrons and Gyratrons replaceable by massive
  arrays of microchips with digital synthesis and
  phase-locked loops. Use in communications and
  radar are routine power transfer needs
  development. Translate optical rectenna RD to mm
  waves
• Advancements in Antennas Antenna
  directionality/gain in 220 GHz regime using DSP.
• Circuits and Switching in the 200-250 GHz regime
• Advancement in Thermal management systems
  Efficient use of waste heat from conversion/
  transmission at high power levels.
• Decentralized grid management through networked
  control
• 200GHz radiation monitoring Health and safety
  issues need investigation
• Compact converters from DC/AC to mmwave and back,
  for micro power systems.
• Smart Grid devices for micro-scale power capture
  and grid input measurements.

36
Conclusions

• BPTS offers a way for technology market and
  convenience to leap-frog the conventional wired
  grid expansion to unconnected areas.
• BPTS using mm waves offers compact size and high
  free-space efficiency. 220 GHz is desirable for
  compatibility with Space Power Grid.
• Several applications including connectivity for
  micro-renewable power systems.
• Basically cost-effective compared to wired grid
  installation, when renewable, fluctuating power
  sources are used.
• DPS / PLL approaches appear to offer more
  efficient and cost-effective conversion to and
  from mm wave regime.
• Technological innovations needed include improved
  antenna design, efficient frequency conversion,
  radiation monitoring, and antenna design.

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The Space Power Grid Synergy Between Space,
Energy and Security Policies
Narayanan Komerath Daniel Guggenheim School of
Aerospace Engineering Georgia Institute of
Technology Atlanta, GA 30332-0150
USA komerath_at_gatech.edu
39
Update on Space Solar Power from New Scientist
Magazine Dec.22. 2008
http//www.newscientist.com/data/images/archive/26
31/26311601.jpg
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Long Term Goal

• Constant, 24-365 solar power available from
  Space. Concepts to build solar power satellites
  are unable to get past the cost to first power
  barrier.
• Problem specification
• How to develop an evolutionary approach where
  revenue generation starts early with small
  investment, and ultimately scales up to
  full-scale Space Solar Power (SSP) in 25-30
  years.
• Viable business plan and minimal costs to
  taxpayers.
• Approach
• Build, market and infrastructure for SSP by
  facilitating terrestrial renewable power.
• Articulate the policy needs and show examples of
  successful practice.

This paper Interplay of technology, economics,
global relations and national public policy
involved in making this concept come to fruition.
41

• GEO Geo-Stationary Earth Orbit
• Satellite stationary 36,000 km above equator.
• 1960s concepts Very large solar-cell arrays in
  GEO, beaming electric power down as microwaves to
  large receivers on Earth. Frequencies ltlt 10
  billion cycles per second (10GHz) are generally
  not absorbed by the atmosphere - selected for
  power transmission.
• NASA etc. focused on GEO-based collector/converter
  /beaming. Consequences
• Frequency must be very good for atmospheric
  transmission lt10GHz.
• Minimum beam diameter is several kilometers for
  this frequency range and distance, regardless of
  power transmitted. ? large stations.
• 2. Assembly at GEO.
• 3. Enormous ground infrastructure.
• 4. Only massive government spending as possible
  funding source.
• 5. Published estimate of 300B to first power
  is based on 1960s estimate of 100 per pound to
  low earth orbit via Space Shuttle. Actual cost
  today is 14000/lb to LEO via SPS
• Real issue is lack of an evolutionary path to get
  the SSP system through initial infrastructure
  development, to a self-sustaining size.

42
New Window Of Opportunity Renewable Power
Climate Control

• Baseload Power criterion forces renewable
  plants to install fossil-burning auxiliary
  generation
• Best locations for wind and solar extraction are
  high deserts, plateau edges, mountain slopes,
  glacier bases and coastlines.
• Insufficient, non-existent or inefficient
  distribution grids over most of the planet.
• Huge temporal fluctuations in power prices
  especially in urban areas.

43
10-fold fluctuation in power costReal-time
retail beaming opportunity
From Landis, G., Reinventing the Solar Power
Satellite http//gltrs.grc.nasa.gov/reports/2004/
TM-2004-212743.pdf
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3-Step Evolutionary Approach to Space Solar Power
Years 6-23 L/MEO constellation enables global
reach for renewable plants in ideal locations.
Revenue from baseload supply and price
differentials. Year 23 Replacement sats
augmented with power converters. Year 23 High
MEO/ GEO reflectors concentrate sunlight on L/MEO
converters to feed grid System expands.
45
Method of Analysis

• Frequency and orbit height ? antenna sizes,
  efficiency
• Power level per satellite ? satellite mass ?
  revenue, of satellites and ground stations
• ? System costs from NASA/USAF FUTRON cost
  models.
• NPV analysis with target cost /KWH, IRR, growth
  model
• System size for breakeven in 17 years.
• Minimum power transaction level per satellite ?
  satellite size
• Effect of public funding on cost per KWH.

Results

• Frequency 200 GHz or greater.
• 60MW handling capacity per satellite
• Startup with 20 satellites and 12 plants
• Phase 1 breakeven in 17 years, grows to 100
  satellites and 100 plants.

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Technology Challenges

• Conversion efficiency to from 200-220 GHz
• Satellite waveguides
• Thermal management
• Atmospheric transmission schemes
• Direct conversion technology for Phase 2
• Ultralight conformable reflectors for Phase 3
  high orbit.

47
Economics Of The Space Power Grid SSP

• Business case is based on 5 features
• Allow solar and wind power plants to
• achieve baseload provider status,
• compete for premium prices by exchanging power
  with plants anywhere.
• locate at prime, remote sites including islands,
• reduce need for backup power generation.
• receive carbon credits, qualify for larger public
  investment.
• 2) Eliminate need for major assembly in orbit,
  minimizes development and launch costs.
• 3) Match constellation size to growth of
  participating plants and revenue.
• 4) Use of a constellation as a power grid
  minimizes the impact of weather by providing
  transmission alternatives.
• 5) Early revenue growth with a few satellites and
  participating plants, eliminating
  cost-to-first-power barrier of GEO-based
  concepts.

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Feature SPG
Steady generation Constellation ensures that some face the Sun at all times, without GEO.
Transmission efficiency Weather dependence alleviated by choice of atmospheric transmission paths.
Infrastructure size Small due to lower orbit (2000km) and high frequency (200 GHz)
Generator Scalable
Installed cost per watt Moderate.
Infrastructure investment Pays for itself on terrestrial power generation. Expands to capture space solar power after break-even. 17 years to improve conversion technology before Phase 2 launch. Phase 3 (high orbit, large area) system is independent of conversion technology on mid-orbit system.

• Breakeven power cost of 30 cents /KWh with IRR of
  8 within 23 years from project start, given the
  first satellite launch in Year 6, with zero
  government funding.
• With 6B govt. investment in development,
  achievable without large increase in system
  efficiency.
• Carbon Credits, savings in transmission
  infrastructure, improve the economics.

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Results Phase 1 SPG, 200GHz, 2000km Constellation
Parameter Value
Satellite Power Level 60MW
Satellite mass 4510 kg
Launch cost to 2000 km high circular orbit 19.8M
Development cost for system 330M
Production cost for 1st 36 satellites 1370M
Ground facilities development cost 1000M
Per satellite annual mission operations and data analysis cost 2.75M
Ground station power level 55MW
Cost of production of power 4 cents / KWH
End-to-end efficiency of beaming power grid 0.3
Sales price at delivery point 30 cents / KWH
Gross margin 5 cents / KWH
SPG share of gross margin 4.5 cents / KWH
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Water Absorption Loss vs. Frequency
http//www.islandone.org/LEOBiblio/microwave_trans
m.gif
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Atmospheric Transmission in the 200-250 GHz
regime
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Special Policy Needs / Opportunities of the Space
Power Grid

1. Global real-time energy trading (expanded from US
   model)
2. Distributed terrestrial transmission
   infrastructure (Smarter Grid, DG)
3. Public acceptance of beamed power from Space
   (IPOD model? )
4. Global technology sharing on Space systems (ITAR
   vs. ESA model)
5. Global Infrastructure Collaboration Model (ESA
   model IATA model)
6. Integration with Utility-Scale Terrestrial Power
   (EU- TRANS-CP)
7. Retail Beamed Power Transmission Systems (BPTS
   paper)
8. Integration with micro renewable power systems
   (MRES paper)
9. Global model for carbon credits (Copenhagen?)
10. Global model for renewables portfolio (EU
    example?)
11. Global model for Infrastructure Avoidance Credit?
    (ESA argument)

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EU TRANS-CP
European Unions Trans-Mediterranean Connection
for Concentrated Solar Power (TRANS-CP) proposes
to set up a high-voltage DC grid connecting solar
plants in the Sahara desert across the
Mediterranean and English Channel to North
Atlantic / North Sea British/German / Dutch wind
generators.
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EU TRANS-CP Recommendations
Policy Issues Financial Benefits
Discrepancy of Awareness and Action Feed-in Tariffs to foster innovation. Renewable Portfolio Standards (RPS) Competitive Bidding for RPS capacity allotments Net metering. Renewable Energy Certificates Green Power Purchasing Grants to producers and consumers Low-interest loans Tax exemptions, rebates Depreciation Demand guarantees, price controls Market access Land access Environmental licenses
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Security Concerns, Space Law and a Global
Infrastructure Consortium

1. Concern about militarization
2. Access to national space facilities
3. Dual-use technologies
4. Competitive issues mixed with security laws
5. Risk of terrorist attack
6. Fear of being excluded from space resources

Opportunity in Crisis Common Imperative

• Shift in security concerns from international
  rivalry to terrorism concerns.
• Thick layer of security at individual level added
  to national criteria.
• New technology and laws provide opportunity to
  rethink space security.
• May render fragmented national rules irrelevant
  and superfluous.

57

• Global Govt Commercial Consortium overall
  framework for private entrepreneurship
• - long-term government-backed financing available
  
• directly provided by participating nations, or
• underwritten by Consortium through private and
  public funds.
• Presence of the Consortium and infrastructure
  cuts lending risk
• cuts loan costs.
• Consortium model provides a consistent economic
  and policy solution.

Consortium Answer to Resource Exploitation /
Property Rights Issue
All resource exploitation ventures must be
multinational public ventures, - open to
investors from all member nations, - limits on
maximum stock ownership to avoid single-nation
dominance - long-term leases awarded
58
CONCLUSIONS

• Obstacles and issues in bringing space solar
  power to earth are discussed.
• Congruence of international interest in renewable
  energy sources and in reducing greenhouse gas
  emissions, provide a window of opportunity to
  bring about Space Solar Power in synergy with the
  development of clean renewable power on earth.
• Policy initiatives advanced in Europe for
  comparable solar power grid project are
  discussed.
• The special features of the space power grid are
  presented, and shown to provide an excellent
  vehicle for global collaboration. While
  substantial technical challenges remain, there
  are viable paths for these challenges, as well as
  for the economics and public/ international
  collaboration needed to make Space Solar Power
  available to humanity.
• Public policy initiatives needed for renewable
  energy, are already acceptable in many nations.
• Security concerns that appear to pose formidable
  obstacles are cited as also posing unprecedented
  opportunities for wel-controlled collaboration
  between nations, through the participation of
  personnel who are cleared at the individual
  level, and through sequestering of technologies
  particular to the project as done in the European
  Space Agencys projects.
• The European TRANS-CP project is cited as a
  relevant current initiative to develop suitable
  policy.

59
Business Case
The business case is based on 4 features 1)
Enabling development of new solar and wind power
plants by boosting their competiveness Qualify
these plants for larger public investment. 2)
Early revenue growth with a few satellites and
participating plants Minimizes
cost-to-first-power obstacle of GEO-based
concepts. Constellation growth is matched to
commissioning of renewable power plants
Reduced lag between investment and revenue
generation 3) L/MEO satellites small
antenna size and beam width compared to GEO
Global reach Eliminates need for major
assembly in orbit, Minimizes development and
launch investment. 4) Minimizing the impact of
weather by providing different alternatives for
power transmission to the ground-based grid.
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Previous Work

• Boechler STAIF 2006
• Achievable end-to-end efficiency
• Near-term no better than 50 of present
  terrestrial urban grid
• Long term (direct conversion from broadband solar
  to beamed narrowband) match or exceed that of the
  terrestrial grid.
• Komerath , IAC 2006
• System based on 140 GHz regime and a
  constellation of 36 sun-synchronous satellites at
  800km altitude.
• Efficiencies not at the levels achieved in the
  2.4 GHz regime.
• Komerath,AIAA Space 2008
• Compared the economics of using different
  frequencies and choices of orbits. Frequency lt
  100 GHz not viable.
• Combination of near-equatorial, polar and
  elliptic orbits can offer the necessary features
  of long transmission times from power plants, and
  retail worldwide power delivery.

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Orbits and Transmission Scenarios

• Scenario 1 Near-equator plants and receivers
• 2000 km orbit height
• Access time within 45-degree cone, of 7 to 10
  minutes at ground stations.
• For stations near the equator, the first several
  satellites are placed in orbits near the equator.
  
• Thus a system start-up with as few as 6
  satellites and 12 plants can be considered.

62
Scenario 3 is High Latitude, Burst-Mode
Transmission
Burst-mode transmission for a few seconds (up to
2 minutes at 60 degree latitude, more at higher
latitudes) may be repeated at regular intervals
essentially through each day and night, with only
a few satellites.
Scenario 4 is the Steady State Phase 1 SPG As
the number of satellites rises, sun-synchronous
orbits become viable for continuous transmission.
For the 1900km sun-synchronous orbit, 72
satellites are needed, which is well below the
expected number of satellites in an established
SPG system.
63
CONCLUSION
64
Opportunity
How can we achieve self-sustaining growth toward
space solar power with reasonable investment
level? 1. GEO SSPImmense receivers, sats and
cost-to-first power. 2. SPS2000 LEO sats beaming
over wide areas 3. Temporal and geographic price
differential compensates for losses in beamed
transmission (Landis, Bekey et al). 4.
Renewable-energy plants need large backup fossil
generators or storage for baseload status. 5.
Ideal solar and wind plants sites are deserts,
high plateaux and mountain ridges remote but
low atmospheric losses. 6. Near millimeter wave
regime compact antenna/receivers 7. Window of
support for synergistic development of power
plants and SPS distribution infrastructure. 8.
Solutions on the horizon for AC- near mm beam
conversion efficiency problem, direct solar
conversion to mm wave, and spacecraft high-power
thermal management?
65
SPG Status Summary

• Synergy with terrestrial renewable power
  economics brings large policy advantages.
• 220 GHz and laser advantages in sizing, orbit
  selection and ground facility
• design, outweigh additional losses in atmospheric
  propagation.
• 2. System calculation sized for 220 GHz may work
  much better with lasers depending on conversion
  and beaming.
• 2. Lower limit of power per spacecraft for
  breakeven 60 MW.
• 3. Initial power plant output levels just below
  capacity of spacecraft.
• 4. Orbit height at 2000 km above Earth enables
  system startup with
• 6 satellites and 6 power plants. Initial launch
  in Year 6.
• 5. Expand to steady state size of 102 sats and
  101 power stations for 30-year break-even.
  Replace sats with augmented ones after 17 years
  of operation.
• 6. Phase 1 system in isolation breaks even with
  no public up-front grants, and a 6 percent ROI
  over 30 years.
• 7. Public funding lt3B in first 10 years brings
  delivered price of power from 30 cents to 24
  cents per KWH.
• 8. Phases 2 and 3 can be started at Year 23 with
  replacement satellites, on a profitable Phase 1
  market and infrastructure.

66
Once Phase 1 is shown to be self-sustaining,
Phases 2 and 3 become much easier

• Replacement or additional satellites in Years 23
  onwards, incorporate receiver/converters
• sized for 160MWe each. High-intensity design
  to capture 100 suns or more in intensity. ( 80m
  dia))
• Brayton cycle thermal management with auxiliary
  power generation at other frequencies.
• Dual frequency system would enable use of 200GHz
  for space-to-space beaming and low frequencies
  for atmospheric propagation.
• Constellation of ultralight collectors in high
  orbits (to minimize drag) to focus broadband
• sunlight to the receivers. Launch cost to high
  orbits minimized.
• 200-satellite constellation would generate 32GWe.
  Equivalent to 320 new nuclear reactors.
• As high-intensity converter technology advances,
  200 satellites may handle upto 320GWe.
• Limited by acceptable size of L/MEO
  constellation.

67
Long-Term Technical Issues

• Present show-stopper Conversion efficiency to
  and from 220GHz (or lasers) for Phase 1.

• Finding ways around the atmospheric propagation
  loss
• - using terrestrial grid to avoid places of bad
  weather
• - tuning to narrow bands power levels for
  optimal transmission
• - Different systems for space-space transmission
  and atmospheric.
• Backup Option
• - In phase 3, LEO-LEO transmission may not be
  needed, so we can use lower frequencies,
• suited to larger power levels and
  spacecraft sizes.
• 3. Spacecraft thermal management with multistage
  power generation.
• Concepts for upto 10MW being studied.
• 4. Direct conversion from broad-band solar for
  Phases 2 3. Efficiency and mass per unit
• power.
• - High intensity solar cells
• - Broadband/ multiband stacked cells
• - Optical rectennae
• 5. Breakthrough in efficiency and mass per unit
  power of converting between
• 200GHz and 5.8GHz regimes.

68
Summary of Recommended Approach
Long-term solution Years 6-23 Space Power Grid
transacting power between renewable plants Years
20 - 30 Full scale SSP growth.
Forward Base Retail Delivery Year 1? Ship to
base using UAV / LTA reflector. Need to ensure
air dominance. Use either radar frequencies or
lasers. (no need for solar power here) Year 6
Regional power plant to base with LEO satellites
(6 needed for continuous transmission. Cheaper
power generation - renewable or not). Year 6
CONUS plant with L/MEO satellites (SPG phase 1
Renewable power plants) Year 15? SSP collectors
in high orbits, L/MEO converter/retail beaming
satellites. (SPG Phase 3 Use space solar power)

• Research priorities
• Conversion efficiency to and from beamed energy
• Direct conversion from broadband to beamed
  energy efficiency and mass per unit
• power.
• - optical rectennae
• - lasers?

69
ARCHITECTURE
Independent Variables Independent Variables Independent Variables
Parameter Baseline Why
Orbit height above surface 880 1200 km Launch cost, antenna size, sun-sync orbits, retail beaming
Atmospheric transmission frequency 200-245 GHz Reduce antenna sizes, avoid water bands
Internal Rate of Return 8 Infrastructure Consortium
Phase Array transmission 45 deg. half-angle Cover 90 degree azimuth of sky
Initial number of ground stations 100 Revenue generation rate
Initial number of satellites 36 Near-continuous beaming
70
SPG Satellite System Characteristics
71
Business CaseParameters for Phase 1 Space Power
Grid
72
Parameters for Phase 2 Augmented SPG
73
Phase 3 Full Space Solar Power Parameters Phase 3 Full Space Solar Power Parameters
Collector Diameter 3km
Satellite Mass 0.015kg/m2 106029
Per satellite cost, M 100
Launch cost _at_10000/kg, M 1060
Solar collector efficiency 0.995
KWh per year per SSP sat, at 100 duty cycle 80E09
End-to-end efficiency 0.4
Cost of production 0
Sales price, per KWh, Phase 2 0.15
Gross profit per KWh 0.06
Gross profit per year per Augsat, M 4806
Total KWh per year added by 96 sats 7.69E12
Note MEO satellite costs still exceed 110B for
100 collectors (300 sq km of solar collection),
but at realistic launch cost, and in a staged
manner over 40 years, tied to revenue generation
74
Prior Work

• Direct Approach
• 100 megasatellites in GEO, large earth stations.
  2.4GHz beams.
• Step-by-step approaches
• All involve satellites and beaming from GEO or
  beyond, or lunar power plants and earth-based
  receivers. (Large beam spread, high cost of GEO
  access)
• Cost of earth-based receivers, and marginal cost
  per installed watt of power in space,
• continue to be large.
• Bekey et al (IAC1995) Beam Canadian power
  through GEO reflectors to Japanese ground station
  with reservoir. 35 Internal Rate of Return
  projected.
• Recent concepts
• SPS2000 Retail, wide-beam power beaming from LEO
  sat (Nagotomo, 1991).
• Modular GEO sat, each module self-contained
  (IAC2005)
• Laser beaming (IAC2005)
• Direct-conversion laser with 38 efficiency
  (Saiki, IAC2005)

75
End-to-End Efficiency Projections
Conventional terrestrial 40conversion from
solar to DC (using best technology) Near 100
conversion to hi-voltage AC. 94 delivered to
end-user. Total 38 of original solar.
Short-term 50 of conventional Long-term
Slightly better than conventional
Short-term using SPG 40conversion from solar
to DC 70 conversion DC to microwave 0.9x0.9 for
atmospheric traverse 0.98 for in-space
transmission 90 conversion from microwave to
useful power Total Short-term 20 of original,
delivered to end-user. Long-term 50 direct
conversion, solar to microwave 36 of original
solar delivered to end-user Full SPS 99
capture from GEO only one atmosphere pass. 39
of original solar delivered to end-user
76
Ground Component

• Ground stations located at ideal solar / wind
  collector locations.
• US Southwest, South Dakota, Hawaiian Islands,
  North African, Gobi, Thar and Australian deserts
  and Greenland are examples envisaged.
• Retail receiving stations on the ground can be
  located almost anywhere - much smaller than
  those for GEO-located SSP systems.
• No need to co-locate receiving stations with
  generator stations except for power smoothing.

77
TECHNOLOGY ISSUES

• LEO sats alleviate launch cost.
• Serve sites at extreme latitudes with minimal
  atmospheric transmission penalties.
• Shorter transmission distance (1,200km to LEO
  vs. 36,000 km to GEO) - smaller receivers.
• The limiting transmission is between satellites
  (2,400 km) or less.
• Waveguides to distribute incoming power.
• Heat rejection issue No more complex than for
  SSP partial recovery using thermo-electric
  systems
• Tradeoffs
• 10GHz range Low absorption, but large receivers/
  less efficient reception Interference.
• 95 - 140 GHz small receivers, more efficient
  reception. Higher atmospheric absorption.
• Forces ground stations to dry, high
  locations.
• Cloud cover problem alleviated by having LEO
  system. Multiple choices of beam path.
• Tradeoff between system mass costs, atmospheric
  absorption and unreliability due to weather
  (alleviated by having multiple earth station
  choices separated by several kilometers) not
  properly understood, since much of the
  high-frequency data comes from astronomical
  observatories until now.

78
Direct Conversion to Microwave

• 1950s Solar-Powered Masers with projected
  efficiency of 50
• 2005 Solar-Powered Laser with 38 efficiency
  demonstrated.

• Direct Solar Conversion to microwave beams with
  50 efficiency and reduced mass by 2035.
• To replace current global production with solar
  energy at 50 efficiency, 5600 sq.km of solar
  collector area in space (where solar intensity
  is 1GW/sq.km) is required.

• SPG satellites will then be replaced with Direct
  Conversion Augmented-SPG (DCA-SPG) satellites,
  with a 1km diameter sun-tracking ultra light
  collector and converter on each adding 0.5 GW to
  the grid.

• Deploying large ultra-thin collectors with
  high-intensity solar cell arrays is an
  alternative to any Direct Conversion technology,
  alleviating technological risk.

79
Full Space Solar Power Phase

• GEO sun-sats (2040s?) 100 sq.km ultra light
  collector/ reflectors that focus sunlight onto
  the 1sq.km collectors of the DCA-SPG.
• Each is expected to add 50GW to the grid at 50
  efficiency.
• System of 72 LEO satellites and 72 GEO ultralight
  mirrors, with a 70 transmission efficiency, will
  generate 90 of todays global energy production.
  

80
Cost

• Baseline sizing to recover 50 of system
  deployment cost in 20 years from savings in costs
  of ground transmission, based on current cost of
  long-term debt.
• Satellite cost lt cost of replacement GPS
  satellite.
• Basic cost of delivered power from SPG is twice
  that of US domestic power cost (efficiency is
  only half as much).
• Advantages yet to be quantified
• Use excess power from spikes in generation at
  green plants (wind / solar).
• Deliver to peak-demand locations (greater
  revenue)
• Access markets with much higher present-day costs
• Market for beamed power in Space
• Industries enabled by point retail delivery
  anywhere on Earth
• Disadvantages of The Competitors, Yet to Be
  Quantified
• Kyoto Protocol / equivalent CO2 penalties
• Added costs to nuclear energy generation/ waste
  disposal costs

81

• Comparison with Conventional SSP and Terrestrial
  Solar

SSP SPG Terrestrial Solar
Energy Production Primary solar generation Exchange new terrestrial plants, Augmented SPG, then Full SSP Constrained by duty cycle, location
Launch cost gt13,200/kg to GEO 6,600/kg to 1215km alt. orbit N/A.
Space Mass gt1kg/kw lt0.01kg/kw for SPG phase 0.1 kg/kw in DCA/SSP phases N/A
Cost Items to First Power Sats grnd recers Space system ground xmission recng control. Gnd system line land costs.
Duty cycle 24hr w/ reflectors 24 hr with multiple sources 6hr/day weather
Assembly LEO assembly, boost to GEO Pre-assembled deploy in LEO. Earth construction
82
CONCLUSIONS

• SSP can be made viable by integrating new
  realities of environmental and energy policy
  issues.
• Space Power Grid uses LEO to exchange power
  across the world - market opportunity.
• End-to-end efficiency shows beamed power
  transmission to be inferior to transmission via
  high voltage lines if only US/European domestic
  markets are considered.
• Long-term end-to-end efficiency superior to
  present power grid.
• However, a space-based power grid opens up
  various markets and opportunities that are
  otherwise closed.
• Present concept provides a revenue-generating
  evolutionary path towards SSP
• Key breakthrough sought is in high-efficiency
  solar-powered Masers.
• Current advances in solar-powered lasers offer
  hope.

83
Our Approach 3-Stage Evolution
1.Microwave converters and beaming equipment
installed. 2. Thirty-six 200-MW SPG satellites
launched. 3. SPG in operation. 4. Direct
converter-augmented satellites DCA-SPG 5. SSP
collector beams sunlight to SPG Full Space Solar
Power