Update on Over the Horizon Wireless
Power Transmission (OTH-WPT)
A Low-Cost Precursor for Laser Space Solar Power
Paul Jaffe, U.S. Naval Research Laboratory
Tanwin Chang, Deep Phase Labs
Bert Murray, Lighthouse Dev
Robert Winsor, Lighthouse Dev
This work is dedicated to the late New York Institute of
Technology Professor Stephen Blank
Overview
•
•
•
•
•
•
Motivation
Laser SSP Concepts
Laser Power Beaming Demonstrations
Wavelength Trades
SSP Concepts with High-Altitude Elements
Proposed Terrestrial Demonstration
Demonstration Motivation
• The high cost of getting to space has been an
obstacle to demonstration implementations
• Over the Horizon Wireless Power Transmission, OTHWPT, is proposed as a low cost precursor to SSP that
does not require access to space
“...large-scale demonstration of power beaming is a
necessary step to the development
of solar power satellites.”
– Geoffrey Landis, scientist and author
Selected Laser SSP Concepts
EADS Astrium Concept, circa 2010
Two-stage SSP Concept
JAXA Concept, circa 2011
Tethered aerostat could be used instead of
microwave beam from high altitude platform (HAP)
Selected Laser Power Beaming
Demonstrations
EADS Astrium tracking laser to power rover, circa 2003
Kinki Univ. & Hamamatsu Photonics Inc. laser power to
small helicopter, circa 2007
Lighthouse Dev Eye-safe laser demo http://www.bbc.co.uk/programmes/p00yjt99 5:40, circa 2012
Lasermotive outdoor laser power to UAV, circa 2012
Comparison of Microwave and Laser
Power Transmission for SSP from GEO
Microwave
Laser
Transmit frequency
5.8 GHz
1.4 mm
Transmit Aperture Diameter In GEO
1 km
2.5 m
Receiving Aperture Diameter On or
Near Earth
3.2 km on earth
40 m
Demonstrated Transmitter
Conversion Efficiency
~80%
~30%
Demonstrated Receiver Conversion
Efficiency
~90%
~50%
Vulnerability to Weather
Probably negligible
Not negligible*
Spectrum Allocation Challenges
Likely to be high
?
International Political Challenges
?
Likely to be high*
*this problem may be reduced or eliminated by using a high altitude receiving platform
Laser Sources at Ten vs. One micron
10.6 microns
1064 nm
Transmit frequency
~ 30 THz
~ 300 THz
Laser Technology
CO2 Sealed Gas
Laser
Diode Pumped Fiber
Laser
Cost per watt (COTs)
< $100 per Watt
~ $100 per Watt
Demonstrated Transmitter
Conversion Efficiency
> 20%
> 30%
Demonstrated Receiver Conversion
Efficiency
TBD
~50%
SWaP (turn-key system)
< 10 kg / 100 W
< 5 Kg / 100 W
Laser Safety Challenges
“Eye Safe”
Cornea is transparent
Space to Tethered Aerostat SSP
• Beaming from space to a high altitude tethered
aerostat avoids main effects of atmospheric
attenuation
• Potentially allows use of “eye-safe” laser transmit
frequency which results in far smaller apertures vs.
microwave for: transmit antenna in GEO and receive
aperture on the aerostat
What is Proposed?
• Long Range Wireless Power Beaming using a
ground-based high-power laser and a high-altitude
receiving platform
• 100s of km range
• Delivery of 100s of kW electric power
• Many other configurations are possible to meet
variety of range, power, weather and tactical
needs
• Perhaps leverage existing “directed energy” assets
Demonstration Configuration
OTH-WPT Goal & Conclusion
• Provide deployable, portable, long range,
economical power transmission for civil,
commercial, and security applications
• Over the Horizon Wireless Power Transmission
represents an achievable, low-cost precursor
for Space Solar Power
Backup
OTH-WPT Functional Block Diagram
(dotted
indicates
optional
element)
Laser Power Converter
Panel
Trihedral
Reflector Panel
Beam
Path
Pilot Signal
Wavefront
Sensor
Power
Supply
High Voltage
Power
Conversion
Tether
Control
Electronics
Laser
Adaptive
Optics
Ground Location 1
Aerostat or
Airborne
Platform
Steering
Mirror
Power
Conditioning
& Distribution
Ground Location 2
Frequency/Wavelength Comparison for a Terrestrial WPT Link
with 10m Apertures & 100km Range
2.45 GHz
5.8 GHz
34 GHz
94 GHz
1.0 μm
Eff. Rx
1.5 μm
“eye safe”
90.6%†
82.7%†
~70%†
~37%†
44.7%
44.7%iii
Eff. Tx
62%ξ
82%iv
73%
25%
53%i
64%
Atmospheric
Attenuation
Negligible
Negligible
Negligible
Negligible
>50%ii
<10%ii
Safe power
density limitv
1mW/cm2
1mW/cm2
1mW/cm2
1mW/cm2
0.09W/cm2
0.08W/cm2
Regulatory
challenges
Wifi
Bluetooth
Minimal
Possible
FAA issue
Possible
FAA issues
Yes
Yes
Total
Efficiency at
100 km*
1%
4%
16%
6%
23.7%
28.6%
*with a transmitter radius of 10 m and a receiver radius of 10 m, 100km range
†Receiver
Efficiencies: Durgin; Valenta (2014) Harvesting Wireless Power
ξ http://www.microwavejournal.com/articles/9441-a-compact-high-power-2-45-ghz-microwave-generator
χ Assuming a Gaussian Distribution, 10dB, and 21 receiver elements
i McCormic School of Engineering and Applied Science
ii http://people.bu.edu/clemens/mimir/atmospheric_transmission.html
iii Dimroth, F, Wafer Bonded four junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cells with 44.7% efficiency, Progress in
Photovoltaics (2014)
Iv McSpadden, James, Design and Experiments of a High-Conversion-Efficiency 5.8 GHz Rectenna (1998)
v ICNIRP . "On Limits of Exposure to Incoherent Visible and Infrared Radiation." 2013. Report.
Green = Better
Yellow = Okay
Red = Worse
Adapted from a
chart created by
Mickey Da Silva
for DHS
Range as a function of air platform height, (km),
(atmospheric attenuation effects not included)
300
r ( h) 200
100
0
2
4
6
h
8
10
Estimated Transmission coeff., T(L,h), at λ= 1.06 μm
as a function of air platform height (h km) and
horizontal beaming distance (L km)
Demonstration
Configuration
• Advantages:
• Atmospheric attenuation one
direction only
•Power easily sent to multiple
locations
• Disadvantages:
• Requires tether
• Potential radiation hazard
Converter
Panels
Power
Down
Tether
Notes:
Airship altitudes above
troposphere
Transmitter
Airborne Reflector Configuration
• Disadvantages:
• Atmospheric attenuation both directions
• Potential radiation hazard
• Advantages:
• One airship
• No tethers
Reflector
Note:
Tether could be used with
airship if desired.
Transmitter
Converter
Panels
Airborne Reflector Configuration
• Advantages:
• One airship
• No tethers/power cables
• Disadvantages:
• Atmospheric attenuation both directions
• Potential laser radiation hazard
Power Beam Down Configuration
• Advantages:
• Atmospheric attenuation one
direction only
• Power easily sent to multiple
locations
• Easier logistics at receiving site
• Disadvantages:
• Requires tether
• Potential radiation hazard
Transmitter
Power
Up
Tether
Converter
Panels
Beam at Altitude Configuration
• Advantages:
• Minimizes atmospheric attenuation
• Very long range, potentially > 1000 km
• Power easily sent to multiple locations
Converter
Panels
Power
Down
Tether
Notes:
Airship altitudes above
troposphere
• Disadvantages:
• Two airships
• Requires tethers
Transmitter
Power
Up
Tether
Beam at Altitude Configuration
• Advantages:
•
•
•
•
Minimizes atmospheric attenuation
Very long range, potentially > 1000 km
Power easily sent to multiple locations
Little or no radiation hazard
• Disadvantages:
• Two airships
• Requires tethers/power cables
Design Challenges
•
•
•
•
•
•
•
•
•
Airborne/field deployable high power lasers
Beam pointing, tracking, retro-directivity
Compensating for atmospheric effects
Mirrors for high power lasers
Laser power conversion
Laser radiation safety
Air platform: high altitude, long duration*
Tether: light weight, low resistance, high voltage
Air traffic control
* Aerostats currently operate at 4-5 km with up to 90
mph wind survivability.
Hardware Sources
• High power lasers:
– IPG Photonics
– Teradiode
• Beam Control:
– Lighthouse Development
– Adaptive Optics / Northrop Grumman
– Boeing
– Lasermotive
• Aerostats:
– ILC Dover
– T-com
• Laser energy conversion:
– Spectrolab
– JX Crystals
Radiation Safety
•
•
•
•
Interlocking intrusion control
Beam pointing positive control
Power density limitations
Wavelength choice to minimize potential
radiation hazard to personnel, animals and
equipment, (1.5 mm or longer, eye-safe)
Technical Issues
• The amount of loss along the tether during
the transmission of the electrical power to
the ground is an important technical issue.
• This loss can be reduced through the use of a
low resistivity conductor and the choice of a
high voltage for transmission.
Technical Issues
• Clouds can occur at operational altitudes.
• Statistical analysis of meteorological data show that
the probability of occurrence decreases with
altitude and is not statically significant at altitudes
above 6 km.
• ref: i) Chilbolton Observatory, UK
ii) Cloudnet, 2007, http://www.cloud-net.org/
St: stratus, Sc: stratocumulus, Nb: nimbostratus; Ac: altocumulus, As: altostratus; Ci:
cirrus, Cs: cirrostratus, Cc: cirrocumulus; Cu: cumulus, Cb: cumulonimbus.
Density of Air vs. Altitude
http://www.aerospace
web.org/question/atm
osphere/q0046b.shtml
1.6
1.4
Atmospheric Density
1.2
1
0.8
0.6
0.4
0.2
0
Altitude
http://www.braeunig.us/space/atmos.htm
Lighter Than Air (LTA)
Aerostats
Heavy Lift
High Altitude
Airships
ABC A60
56K
ISIS
4.2M TowTech
PTDS 74K
HALE-D
SkyTug
Zeppelin
TARS 420K
MA-3
HAA
StarTower
LEMV
GNSS 40K to 80K
Lightship
Tethered Aerostat with ground station
Tether properties
Aerostats, widely used, U.S. mfg. items.
Air Platform Technical Issues
• Strong winds and lightning at operational
altitudes and possible interference of the
aerostat with aviation.
• These problems are common to other high
altitude aerostats used for surveillance
purposes, which survive 90 mph winds, have
lightning protection and carry warning
systems to avoid collision with air traffic.
• Powered stabilization will be studied.
OTH-WPT Portability
• OTH-WPT would be highly portable and relatively
economical
• Aerostat and ground system could be moved with
relative ease
• Portability of great importance in providing
power to remote areas on an emergency basis
and to theaters of operation that are rapidly
changing
• Hard-wired power lines or fuel trucking are often
not feasible or are very expensive to remote
areas
Future Material
• Historically relevant work:
– Fischer
– AFRL Directed Energy demo to crane suspended mirror
• Graphical range comparison showing advantage of
aerostat over tower
– Geometric advantage
– Reduced atmospheric attenuation advantage
• Actual FOB example case, AFG?
• Fully-burdened cost of fuel vs. laser eff etc.
• Power density & receiver area explanation
Electromagnetic Waves
High Frequencies
Blocked
http://www.rfcafe.com/references/electrical/ew-radar-handbook/images/imgh51.gif
Low Frequencies
Admitted
10.6 Micron Conversion Options
• Useful photovoltaics do not exist at 10.6
microns due to the inefficiency of generating
power from a small band-gap material
• Heat engines are a potential solution, but not
ideal at 10.6 microns due to the relatively
large spot size of the transmitted beam
• Microscopic antennas with diode rectification:
Rectennas, or “Nantennas”
Nantennas
• Combination of a lithographically produced
bowtie antenna with geometric (ballistic) diode
Anode
Cathode
Bowtie
Antenna
Graphene
Geometric Diode
Depiction adapted from Joshi, S.; Zixu Zhu; Grover, S.; Moddel, G., "Infrared optical response of geometric diode rectenna solar cells,"
Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE , vol., no., pp.002976,002978, 3-8 June 2012
WPT Considerations for Most Contexts
• Tradeoff between Tx/Rx area and power density
depending on safety requirements, available
collection area
• Factors affecting availability: atmospheric
conditions, source reliability, susceptibility to
single-point failures
• Regulatory, safety, and incumbent user issues
• Cost & utility vs. alternatives
WPT Modality: Space-to-Space
• Applications
– Fractionate spacecraft
– Enable power for very low orbit or low-profile spacecraft
• Notes
– Must have compelling advantage over widely available
1400W/m2 sunlight, such as minimizing drag
– Could make “safe/hold” mode challenging if no battery or
PV backup
– Potential laser advantage since no atmospheric
attenuation and minimal eye safety concerns
WPT Modality: Space-to-air/sea/ground
• Applications
–
–
–
–
Classic space solar power applications
Disaster response power
Space launch
See applications from NRL SBSP report next slide
• Notes
– Ability to send power to locations within a huge
global area may present a compelling advantage
– Power would be quickly redirectable without grid
losses or extant infrastructure
– Economic case challenging to make
Outline
From NRL
SBSP report,
prospective,
military power
beaming scenarios
WPT Modality: Ground-to-air/space
• Applications
– UAV dwell extension/power augmentation
– Element of disaster response/battlefield power
transmission network
– Space launch
– Enable power for very low orbit spacecraft
• Notes
– Extended UAV operations without power beaming
already demonstrated
WPT Modality: Sea/ground-to-sea/ground
• Applications
– Ship to shore power beaming, vice versa
– Power for sensors in denied areas
– Power to/from/between FOBs/COPs with towers
or aerostats
• Notes
– Potential to use beam expansion with existing
directed energy assets to reduce power density
to “safe” levels
Backup
NRL SBSP Study Group Summary Findings
• Finding 3, Military operations scenarios:
– SBSP systems employing microwave power transmission at
frequencies below 10 GHz are most suited for a limited number of
bases and installations where the large area required for efficient
power reception would be available.
– For applications requiring smaller apertures, millimeter wave or laser
power transmission may be preferable, though tradeoffs between
safety, increased atmospheric attenuation, and received power
density must be addressed carefully.
– Direct power transmission to individual end users, vehicles or very
small, widely scattered nodes does not currently appear practical,
primarily because of the large inefficiencies and the possible risks of
providing what amounts to a “natural resource”.
– Backup alternatives should be considered for installations in the event
of failure, compromise, or military action as an SBSP system may
present the problem of a single point of failure.
2008-09-30
SBSP 47
Finding 3, SBSP Military Operations Scenarios
Background Chart (1 of 2)
• Forward Operating Base Power
– Possible, but likely only applicable to fairly large installations.
• Bistatic radar illuminator
– Possible.
• Provide power to a remote location for synthfuel production
– Possible, but requires considerable infrastructure, feedstock, and forces that
could exploit the products.
• Power for distributed sensor network
– Unlikely. Power densities, inefficiencies of widespread isolated receivers, and
possible enemy exploitation of “natural resource” are problematic.
• Power to Individual End Users
– Unlikely. Similar problems to the above, with the added concerns of extreme
precision beam control and possibly unsafe power densities.
2008-09-30
SBSP 48
Finding 3, SBSP Military Operations Scenarios
Background Chart (2 of 2)
• Space solar power to non-terrestrial targets
– Satellite to satellite power transmission
• Possible, but poses significant system design problems, and may not
compare favorably to direct power collection.
– Space to UAV for dwell extension
• Small, moving target challenges wireless power beam control; multi-day
solar UAV flights may render this application irrelevant.
• Terrestrial Wireless Power Beaming Applications Apart from
SBSP
– Ship to shore power beaming
• Possible, requires refinement of wireless power beaming technologies.
– Ground to UAV for dwell extension
• Same issues as “Space to UAV”
2008-09-30
SBSP 49
NRL SBSP Study – Revisit Efficacy of
SBSP
Recommendations from “Space-Based Solar Power
As an Opportunity for Strategic Security”,
National Space Security Office Phase 0 Report (Oct 2007)
Recommendation #1: The U.S. Government should organize effectively to allow for the
development of SBSP and conclude analyses to resolve remaining unknowns.
Recommendation #2: U.S. Government should retire a major portion of the technical risk
for business development.
Recommendation #3: The U.S. Government should create a facilitating policy, regulatory,
and legal environment for the development of SBSP.
Recommendation #4: The U.S. Government should become an early
demonstrator/adopter/customer of SBSP and incentivize its development.
(Areas of possible NRL contribution)
2008-09-30
SBSP 50
Terrestrial Power Beaming
• Sending energy wirelessly may offer utility for military, disaster
recovery, or grid-infrastructure deficient areas
• Laser and mm-wave allow smaller transmit and receive
apertures vs. microwave
• Safety and cost are key considerations
• Using an aerostat or other airborne platform for the power
transmitter or receiver can greatly enhance the range
• Successful terrestrial power beaming could pave the way for
space solar power
Escape Dynamics mm-wave Power
Beaming for Space Launch
• Building their own gyrotrons
• Demonstrated higher than chemical Isp in July
2015
SLIDE CONTENT FROM BERT MURRAY, LIGHTHOUSE DEV
Eye-Safe Laser Power Beaming Demo at the
University of Maryland
•
•
This effort demonstrated the ability to remotely power devices using an
(unaided) eye-safe laser beam
Range of demonstration was much shorter than possible
– Demonstrated range of 240 meters
– Range of up to 2km would have been feasible
•
This technology offers unique capabilities not found elsewhere in industry:
– 1000 times smaller area hazard zone for high-power applications
– 30 times more power than most competing eye-safe systems
– FAA compliant (no special permits needed) for nominal eye-safe beams (not true of
some competing technologies)
•
•
There is a stigma that laser power beaming is terribly dangerous and exotic –
we want to change that!
The fact is that this technology is safe and actually costs less than alternative
power management schemes for some applications
– Such as remote controlled vehicles for unattended sensors
06 October 2013
A collaboration between Lighthouse, LLC
and Eritek, Inc.
SLIDE CONTENT FROM BERT MURRAY, LIGHTHOUSE DEV
Components of the Demo
Receiver:
Transmitter:
•Fresnel Concentrator
•GaSb Photovoltaic
•10 Watts @ 1550nm
– Power can be higher
• With safety wear, training
– 125mm aperture
• Beam Divergence less than 100urad
– Can be focused
•Bore-sighted with visible laser
– 633nm, 5mW
– 50mm beam diameter
– Used to assist aiming
•Voltage conditioners
– Convert voltage, current
– Supply 3.3V
•Powered Equipment
– Bright-white LED
– Transistor Radio
– Small motor
•Rifle-scope viewing aid
– Assists pointing during daylight
conditions
06 October 2013
– 0.35V per cell
– 6 in series
– Max 1.5 watts output
•Raw output can charge single-cell
batteries
A collaboration between Lighthouse, LLC
and Eritek, Inc.
Thank You
• Paul Jaffe, NRL, paul.jaffe@nrl.navy.mil
• Tanwin Chang, Deep Phase Labs,
tanwin.chang@deepphase.com
• Bert Murray, Lighthouse Development,
hcm1955@gmail.com