The Space Power Grid
Narayanan Komerath, Nicholas Boechler
Daniel Guggenheim School of Aerospace Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0150 USA
October 2006
IAC06_C3.4.6, Valencia
Komerath@gatech.edu
Problem Definition
• SSP: Large solar converters at GEO or beyond, beaming to earth.
• Huge cost of GEO access & construction: >$300B before first revenue even
with improbably low launch cost estimates.
Problem:
• How to develop an evolutionary approach where revenue generation starts early with small
investment, and ultimately leads to full-scale Space Solar Power (SSP).
http://img.timeinc.net/popsci/images/space/
space0805eng_485x326.jpg
October 2006
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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)
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Space Power Grid: Key Features
•
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 (Landis
2004, Bekey 1995).
Beam to other satellites
Retail delivery (SPS2000).
Space Power Grid: Redistributing Energy
Technical risks in dynamic
beaming/reception/ transaction
system.
Inefficient conversion to and
from microwave vs. terrestrial
high-voltage transmission lines.
October 2006
FIGURE
1. Space Power Grid Satellite Receving And Redistributing Beamed Power.
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Space Power Grid Phase
•  36 satellites in sun-sync orbits (~880 km) and 100 earth plants using
microwave beams in real-time energy trade.
• Number rises to 100 sats (incl. equatorial, 1200km orbits),
268 earth-based plants.
• Each is assumed to be able to transact power with 4 other satellites
and up to 100 retail customers.
• Internal Rate of Return held at 8% (public-private Global Consortium)
• Cost of renewable energy held down by Carbon Credits
October 2006
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Sizing
Frequency (GHz)
Ground to Satellite
Receiver diameter on sat, m
Orbit height (km)
Transmisssion distance (45 -deg), km
Efficiency of beam capture
Actual diameter of transmitter on ground
Satellite to Satellite
Distance between sats (km)
Antenna diameter, m
2.45
10
200
300
800
1131
0.99
1200
300
1100
1556
0.99
3000
50
800
1131
0.99
500
2400
846
2400
419
2400
94
• 250MW peak power handling per sat.
• 100MW average beaming per ground
station, with 50% usage factor, 12 hrs/day.
• Thermal Protection, Storage and
Regeneration: use liquid + He/Xe
turbopumped cooling.
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ARCHITECTURE
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
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Orbit Optimization Problem
Tracks of a single
Sun-sync satellite
.
Using STK software
• Solar plants to beam up in daytime, receive at night.
• Nuclear plants beam up excess power at night.
• Locate plants under satellite tracks, to have at least one within
beaming cone during beaming periods.
• Minimize transit losses at highest beam power.
October 2006
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Sample Visualization of SPG Operation
October 2006
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Beaming Sample: 3 Satellites
October 2006
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BABY STEPS TOWARDS SPG
• Low-altitude beamed-energy exchangers.
• Long-endurance aircraft as “reflector”
• (transmission across a body of water or larger distance),
• Large balloons at altitudes high enough to qualify as
• the “edge of space”.
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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
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250
1273
127323
38.9
546
2000
400
1000
5000
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 dev elopment 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 pl ant
MWh per year, for 1 plant at 50% duty cycle,
per satellite available (100%=36sats)
October 2006
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30
30
5
1000
1000
25
0.04
0.3
0.2
0.02
100
12175
Parameters for Phase 2: Augmented SPG
Collector/Converter Diameter, m
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
October 2006
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300
70686
7000
42
42
0.25
100,621,000
0.4
0
0.15
0.06
6.04
Phase 3: Full Space Solar Power Parameters
Collector Diameter
3km
Satellite Mass: 0.015kg/m^2
106029
Per satellite cost, $M
100
Launch cost @$10000/kg, $M
1060
Solar collector efficiency
0.995
KWh per year per SSP sat, at 100% duty cycle
80E+09
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
7.69E+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
October 2006
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Architecture Options
a. Use conventional photovoltaics on the LEO satellites, with large-area
collectors
b. Use direct solar conversion to lasers, laser transmission between satellites,
but convert to microwave to beam to earth.
c. Solar-pumped MASER
d. Direct conversion from sunlight to beamed microwave using an optical
rectenna.
Technology Options
• Ultra-Light Reflectors:
• Optical Rectennae:
• Momentum Vector Scheduling
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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 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.
Short-term:
50% of
conventional
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 IAC06_C3.4.6,
to end-user
Valencia
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Net Present Value with 96 SPG-sats and 268 plants, in 20 years
NPV, Space Power Grid, 96 Sats, 268
plants@100MW, 50%duty cycle
0
1
3
5
7
9
11
$M
-2000
-4000
-6000
Year
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13
15
17
19
21
SPG and ASPG Phases: System Growth
300
Energy, TWh
Satellites
Ground Stations
250
200
150
100
50
ASPG
SPG
0
6
October 2006
8
10
12
14
16
18 20
Year
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22
24
26
28
30
Full SSP Phase Energy Growth
120
Energy,
1000TWh
SSP Collector
Sats
100
80
60
40
20
0
31
October 2006
32
33
34
35
36
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Year
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37
38
39
40
CONCLUSIONS
1.
Space Power Grid startup breaks even on $4B investment and 8% IRR, with 36 satellites and
100 ground stations, 10 to 15 years after project initiation. Low generation cost assumes public
support (carbon credits and fossil fuel replacement programs).
2.
Phase 1 Space Power Grid breaks even, with investment of $6B, 96 satellites and 268 ground
stations, within 21 years.
3.
Once system is refurbished with Augmented satellites and SSP collectors in high orbits, power
costs drop.
4.
Final cost of system may be ~ $150B, but with realistic launch costs, and in steps achievable
using the revenue streams from the system
5.
This concept shows how the launch cost problem to geosynchronous earth orbit can be
avoided, and a full Space Solar Power system and its ground infrastructure set up within
40 years, at a manageable and recoverable cost.
October 2006
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Acknowledgements
The second author was supported through a National
Student Fellowship from the NASA Institute of Advanced
Concepts. The first author gratefully acknowledges support
from the NIAC and the MacArthur Foundation through the
Sam Nunn School of International Affairs, Georgia Institute of
Technology, and valuable discussions at the Colorado
School of Mines.
October 2006
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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.
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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.
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Water Absorption Loss vs. Frequency
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http://www.islandone.org/LEOBiblio/microwave_transm.gif
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.
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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 2006
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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
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Comparison with Conventional SSP and Terrestrial Solar
SSP
SPG
Energy
Production
Primary solar
generation
Exchange; new terrestrial plants, Constrained by
Augmented SPG, then Full SSP duty cycle, &
location
Launch cost
>$13,200/kg to $6,600/kg to 1215km alt. orbit
GEO
N/A.
Space Mass
>1kg/kw
<0.01kg/kw for SPG phase;
0.1 kg/kw in DCA/SSP phases
N/A
Cost Items to
First Power
Sats + grnd
rec’ers
Space system + ground
x’mission & rec’ng + control.
Gnd system+ line
+ land costs.
Duty cycle
24hr w/
reflectors
24 hr – with multiple sources
6hr/day; weather
Assembly
LEO assembly, Pre-assembled – deploy in LEO. Earth
boost to GEO
construction
October 2006
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Terrestrial Solar
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.
•
•
•
•
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ACKNOWLEDGMENTS
Part of this work (microwave beaming and direct conversion issues) was conducted in the
course of studies related to a grant from the NASA Institute of Advanced Concepts. SW
and NK acknowledge the support from the John D. and Catherine T. MacArthur
Foundation through the Sam Nunn Security Program in the School of International
Affairs, Georgia Institute of Technology to study the broader policy issues
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1999 World Primary Energy: USDOE
Renewable
1%
Total: 377E15 BTU
Y2020 projection: 599E15 BTU
Coal
23%
Petroleum
39%
Nuclear
7%
Natural Gas
23%
October 2006
Hydroelectric
7%
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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 2006
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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
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