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

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.

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.
4.
It enables synergy with distributed micro renewable power architectures.
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 longdistance 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.

DrDt

S

2.44

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 fullpower 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

Figure 3: Transmission through a dry atmosphere (less than 50mm precipitable moisture). Astronomical observatory data,
Mauna Kea, Hawaii.

Issues And Solutions
Expense of solid state arrays vs. PV arrays

2. Atmospheric Propagation Losses

3. High Beam Intensity

4. Health Effects of Millimeter Waves

4.
Waves
Generation of Millimeter

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 fullpower 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

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.

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 <10GHz microwave, and some proposed solutions using lasers.
• Our interest is in the millimeter wave regime, specifically near 220 GHz
Beam Formation
Transmission & Reception
DC to mm wave conversion mm wave to
DC conversion

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.co.uk/2/hi/africa/8257153.stm
Notes:
1.Original motivation: power a radio to fance to music
2.Business plan: charging station for cellphones.
Lesson: Demand for cellphones and other electronic systems is far ahead of national Power Grid expansion rate.

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.

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

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.

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

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

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

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

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

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

400
375
350
325
300
275
250
225
200
175
150
125
100
75
50
25
0
20 40
Feasibility of low range low efficiency BPTS
BPTS Range (km) vs System frequency (GHz)
Antenna diameter= 20m, 20m
Antenna diameter= 20m, 5m
Antenna diameter= 20m, 1m
Antenna diameter= 30m, 5m
Modified Friis equation calculation shows that antenna combination of
(20m; 5m) is adequate for
100km range at
200 GHz.
(20m;1m) is good for 10 km
60 80 100 120 140 160 180 frequency in GHz
200

0.6
0.5
0.4
0.3
0.8
0.7
20m transmitter diameter, 5m receiver diameter range = 50 km range = 75 km range = 100 km range = 150 km
0.2
0.1
0
0 20 40 60 80 100 120 140 160 180 200

Cost Model, Wired vs. Retail Beamed Power Infrastructure
Wired installation: Effective cost per km (~ US$1M / 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 ~ US$100K/km (1 transmitter/ relay per km)

20
10
60
Cost-effectiveness of BPTS vs. Wired Grid Installation
50 wired bpts

= 8GHz bpts

= 10GHz bpts

= 20GHz
40
30
Even at 20 GHz, BPTS is more cost effective than wired installation for distance less than 6 km
0
0 1 2 3 4 5 6 7 8

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 R&D 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.

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.

300
200
100
600
500
400
Antenna Diameter (m) vs System frequency (GHz) range = 1 km range = 5 km range = 30 km range = 50 km range = 100 km
0
0 20 40 60 80 100 120
System frequency in GHz
140 160 180 200

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@gatech.edu

Update on Space Solar Power from New Scientist Magazine: Dec.22. 2008 http://www.newscientist.com/data/images/archive/2631/26311601.jpg

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.

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 << 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:
1.Frequency must be very good for atmospheric transmission: <10GHz.
2.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 .

New Window Of Opportunity: Renewable Power & Climate Control
• “Baseload Power” criterion forces renewable plants to install f ossil-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.

10-fold fluctuation in power cost:Real-time retail beaming opportunity
From Landis, G., “ Reinventing the Solar Power Satellite” http://gltrs.grc.nasa.gov/reports/2004/TM-2004-212743.pdf

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.

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.

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.

Economics Of The Space Power Grid SSP
Business case is based on 5 features:
1) 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.

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.

Results: Phase 1 SPG, 200GHz, 2000km Constellation
Parameter
Satellite Power Level:
Satellite mass:
Launch cost to 2000 km high circular orbit:
Development cost for system:
Production cost for 1st 36 satellites:
Value
60MW
4510 kg
$ 19.8M
$ 330M
$1370M
Ground facilities development cost: $1000M
Per satellite annual mission operations and data analysis cost: $2.75M
Ground station power level
Cost of production of power
$55MW
4 cents / KWH
End-to-end efficiency of beaming power grid
Sales price at delivery point
Gross margin
SPG share of gross margin:
0.3
30 cents / KWH
5 cents / KWH
4.5 cents / KWH

2008
Water Absorption Loss vs. Frequency

Atmospheric Transmission in the
200-250 GHz regime

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)

EU TRANS-CP
European Union’s 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.

EU TRANS-CP Recommendations
Policy Issues
• 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
Financial Benefits
• Grants to producers and consumers
• Low-interest loans
• Tax exemptions, rebates
• Depreciation
• Demand guarantees, price controls
• Market access
• Land access
• Environmental licenses

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.

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

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 Agency’s projects.
• The European TRANS-CP project is cited as a relevant current initiative to develop suitable policy.

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.

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 < 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.

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.

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.

CONCLUSION

Opportunity
How can we achieve self-sustaining growth toward space solar power with reasonable investment level?
1. GEO SSP:Immense 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?
October
2008

SPG Status Summary
1.
Synergy with terrestrial renewable power economics brings large policy advantages.
2.
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 <$3B 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.
October
2008

Once Phase 1 is shown to be self-sustaining, Phases 2 and 3 become much easier
1.
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.
2.
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.
October
2008

Long-Term Technical Issues
1.
Present show-stopper: Conversion efficiency to and from 220GHz (or lasers) for Phase 1.
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.
October
2008

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:
1.
Conversion efficiency to and from beamed energy
2.
Direct conversion from broadband to beamed energy: efficiency and mass per unit power.
- optical rectennae
- lasers?
October
2008

ARCHITECTURE
Independent Variables
Parameter
Orbit height above surface
Baseline
880 – 1200 km
Atmospheric transmission frequency
Internal Rate of Return
Phase Array transmission
200-245 GHz
8%
45 deg. half-angle
Initial number of ground stations 100
Initial number of satellites 36
Why
Launch cost, antenna size, sun-sync orbits, retail beaming
Reduce antenna sizes, avoid water bands
Infrastructure Consortium
Cover 90 degree azimuth of sky
Revenue generation rate
Near-continuous beaming
October
2008

SPG Satellite System Characteristics
Power transmitted (design, MW)
Average beam intensity, uniform, at ground, w/m^2
Average beam intensity, uniform, at satellite, w/m^2
Antenna mass, kg
Mass for space-space antennae, kg
Cooling system mass: 2000kg/2.5MW
Mass of fluid, for 400K heating in 60 seconds at
2.5MW, kg
Other systems
With margin of 1000 kg, total satellite mass, kg
250
1273
127323
38.9
546
2000
400
1000
5000
October
2008

Business Case:Parameters for Phase 1: Space Power Grid
Launch cost at $6K/kg to 880km, $M
Per satellite cost for one of the first 36, $M
Operations cost per satellite per year, $M
Satellite system development cost, $M
Ground facilities development cost for 1 st 100 stations
Connection cost per additional station, $M
Cost of production of power, $/KWh
Fraction received as useful electric power
Sales price, $ per KWh
Gross profit per KWh
Beamed average MW per plant
MWh per year, for 1 plant at 50% duty cycle, per satellite available (100%=36sats)
30
30
5
1000
1000
25
0.04
0.3
0.2
0.02
100
12175
October
2008

Collector/Converter Diameter, m 300
Area, sq.m
Satellite Mass: Add 2000kg
Per satellite cost, $M
Launch cost @$6000/kg, $M
Solar conversion efficiency
KWh per year per ASPG sat, at 50% duty cycle
End-to-end efficiency
Cost of production
Sales price, $per KWh, Phase 2
Gross profit per KWh
Gross profit per year per Augsat, $M
70686
7000
42
42
0.25
100,621,000
0.4
0
0.15
0.06
6.04
October
2008

Phase 3: Full Space Solar Power Parameters
Collector Diameter
Satellite Mass: 0.015kg/m^2
Per satellite cost, $M
Launch cost @$10000/kg, $M
Solar collector efficiency
KWh per year per SSP sat, at 100% duty cycle
End-to-end efficiency
Cost of production
Sales price, $per KWh, Phase 2
Gross profit per KWh
Gross profit per year per Augsat, $M 4806
Total KWh per year added by 96 sats 7.69E+12
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
3km
106029
100
1060
0.995
80E+09
0.4
0
0.15
0.06
October
2008

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)
October
2008

End-to-End Efficiency Projections
Conventional terrestrial:
40%conversion 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
Short-term using SPG: 40%conversion 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:
Slightly better than conventional
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
October
2008

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.
October
2008

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.
October
2008

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 highintensity solar cell arrays is an alternative to any
Direct Conversion technology, alleviating technological risk.
October
2008

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 today’s global energy production.
October
2008

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 < 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
October
2008

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 >$13,200/kg to
GEO
$6,600/kg to 1215km alt. orbit N/A.
Space Mass >1kg/kw N/A
Cost Items to
First Power
Sats + grnd rec’ers
<0.01kg/kw for SPG phase;
0.1 kg/kw in DCA/SSP phases
Space system + ground x’mission & rec’ng + control.
Gnd system+ line
+ land costs.
Duty cycle
Assembly
24hr w/ reflectors
24 hr – with multiple sources 6hr/day; weather
LEO assembly, boost to GEO
Pre-assembled – deploy in LEO. Earth construction
October
2008

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.
October
2008

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
October
2008