SPACE SOLAR POWER
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NON CONVENTIONAL SOURCE OF
ENERGY
SPACE SOLAR POWER
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Index
Sl no.
Contents
page no.
1.0
Abstract
02
2.0
Introduction
03
3.0
Concept of SPS
04
4.0
What is project
04
5.0
Space power satellite
06
6.0
Microwave transmitter section
08
7.0
Phase controlled magnetron
09
8.0
Beam Control
10
9.0
Receiving station
10
10
Problems and Remedies
14
11
Advantage and Disadvantage
17
12
Conclusion
18
13
Figures
20
14
References
24
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Abstract
Humans are going to need a huge amount of energy in the the coming decades if the Enormous rate
of development and growth of mankind continues. Within 50 years the world population is expected
to be doubled .The existing energy sources already face serious problem and are extinguishable. In
this paper we are sorting out this energy crisis by introducing the concept of Space Power Satellites
(SPS).
Solar energy is present in space in tremendous amount and this can be collected 24 hours a day with
very high and constant intensity being unaffected by clouds and weather. This energy can
be transmitted to earth using SPS.
The basic idea of power from space would catch the flood of energy flowing from the Sun and then
pump it to Earth via laser or microwave beam. On earth it would be converted to electricity and fed
into power grids to be tapped by terrestrial customers.
_
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1. INTRODUCTION
“In looking at our current world situation, I believe that what is most needed
is hope. Power from space may be one of the best means for us to offer that hope,"
Davis told SPACE.com.
Harnessing solar power have been in the endeavors of human effort since decades. It’s
only now the necessity of utilizing radiation energy from sun has taken a leap forward. If
the population grows at its present rate by 2050, it would figure out be around 10 billion.
In order to nourish such (! huge mass only solar power will serve as a limitless source of
energy. Also economic growth has led to the tremendous consumption of the
conventional resources, which is limited in nature and fast depleting .In near future solar
power will exist as the sole option to fuel this economic stride.
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2. SPACE POWER- A limitless source of energy
The solar energy that reaches the Earth is about 10,000 times total human energy
production today and the energy available in near Earth space is limitless. Research is
being done on many different ways of using solar power economically on Earth and
many of these will be successful. Terrestrial solar energy is going to become a colossal
business. However, sunlight is diffuse and not available continuously at the Earth's
surface. So one additional possibility is to collect solar energy 24 hours per day in space,
and transmit it as microwave beams to receivers on the Earth.
According to research by EPRI (Electric Power Research Institute)at an altitude of
22,300 miles from Earth on average sunlight would be eight times as much sunlight as
they would be on the Earth surface. This amount is unaffected by the earth day night
cycle, cloud cover and atmosphere dust Gathering power in space and transmitting it to
earth should not be a mystery in this 21st century.
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3.0 Concept of solar power Satellite (SPS)
The basic idea of power from space originated with NikaJa tesia, one of the founders of
the electric age and discoverer of wireless radio and the idea of beaming solar power
from space was revisited by Peter Glaser at Arthur D Little in the 1960's. Glaser first
proposed SPS in 1968 and in 1973 he received a U.S. patent on a conceptual design for
such a satellite. the concept of large space power satellite (SPS), that would be placed in
Geo-stationary Earth orbit (GEO) to collect sun light , use it to generate electromagnetic
beam and transmit the energy to the Earth, was invented in 1968. Figure 1 & 4
What is the project??
Spurred on by the oil crises of the 1970's, the US Department of Energy and NASA
jointly studied the SP during that decade. The result of this study was a design for an SPS
which consisted of a 5 x 10 kilometer (3 x 6 mile) rectangular solar collector and a 1kilometer-diameter (0.6 mile) circular transmitting antenna array. The SPS would weigh
30,000 to 50,000 metric tons. The power would be beamed to the Earth in the form of
microwaves at a frequency of 2.45 GHz (2450 MHz), which can pass unimpeded through
clouds and rain. This frequency has been set aside for industrial, scientific, and medical
use, and is the same frequency used in microwave ovens. Equipment to generate the
microwaves is therefore inexpensive and readily available, though higher frequencies
have been proposed as well. The rectenna array would be an ellipse 10 x 13 kilometers (6
x 8 miles) in size. It could be designed to let light through, so that crops, or even solar
panels, could be placed underneath it. The amount of power available to consumers from
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one such SPS is 5 billion watts. (A typical conventional power plant supplies 500 million
to 1 billion watts.) T he peak intensity of the microwave beam would be 23 milli -watts
per square centimeter (148 milli watts per square inch).. Nevertheless, even the peak of
the beam is not exactly a death ray. Underneath the rectenna ,microwave levels are
practically nil. (Figure 2.0)
The target launch cost is $2,200 per kilogram--one-tenth that of a shuttle launch. At that
price, space power could become cost-effective if satellites pull double-duty as
communications relays and solar-power sources. A solar power satellite should quickly
pay back the energy needed to put it into orbit. Start with the conservative assumption
that solar power satellite technology would produce 0.1 kilowatt of electricity on the
ground per kilogram of mass in orbit. In that case, the energy expenditure of 10 kilowatthours per kilogram to lift the satellite into orbit would be repaid in electricity after only
100 hours--less than five days.
Improvements have been seen in efficiency of solar cells and production of lightweight,
solar-cell laden panels; Wireless power transmission tests on Earth is progressing,
specifically in Japan and Canada; Robotics, viewed as essential to SSP on-orbit assembly,
has shown substantial improvements in manipulators, machine vision systems, hand-eye
coordination, task planning, and reasoning; and Advanced composites are in wider use,
and digital control systems are now state of the art - both developments useful in building
an SSP.
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4. SPACE POWER SATELLITE (SPS)
4.1 SOLAR PANEL
In Space power satellite (SPS) power will be generated by large Solar panels covered
with Solar cells.A Solar cell consists of photovoltaic cells will convert Sunlight into
Electricity.An array of such cells produce huge amount of electricity.
Solar Cell: The following baseline data used for Solar Cell Unit is based on the current
performance of ground-use a-Si solar cells and their possible evolution in the near
future.
Conversion Efficiency 15 %
Unit Weight
0.22 kg/m2
Specific Power
950 Watt/kg
Thickness
0.2 mm
Array Module: A subarray is composed of 12 solar cell units. The array module,
composed of 110 sub arrays, is a mechanical element for assembly. Each array module
generates 180A at 1 kV. The weight of the array module is 270 kg per each module.
Forty five array modules are assembled in each wing; northeast, southeast, northwest, and
southwest.
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Power Collection and Distribution: The Wing Summing Bus Line(321) collects the
electric power from the array modules. Each bus line has hot and return bus cables. The
bus lines are insulated copper plates 1 mm thick. They get wider as they approach the
center of the SPS2000 satellite to keep the joule loss per surface area constant. The Wing
Summing Bus Lines are connected to the Central Bus Lines(322) which are interfaced
with the spacetenna system. The Central Bus Lines are insulated copper plates 0.7 mm
thick by 100 mm wide. The Bus Lines are mechanically attached to the truss pipes using
insulated adapters. The power loss in the bus lines is 7 % in total. The total weight of the
power lines is approximately 11,000 kg. The Sun Tower power Satellite concept
concentrating thin.-film reflectors would focus Sunlight on to multi-band gap Solar
modules of about 1 MW each. A multi-strand High Temperature Superconductivity Cable
(HTS) would connect the modules.
A constellations of 20 such solar satellites could provide a total of 20 to 80 GW divided
among multiple rectenna sites on the Earth.(figure 3.0)
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Electrical Characteristics
Frequency
2.45GHz
Beam control
Retro directive
Beam scanning angle
+30 degrees (east-west)
Power distribution
constant
Power density
574W/m2
Max. power density on ground
23mW/cm2
Input power to spacetenna
16 MW
Transmitting power
10 MW
Mechanical Characteristics
Shape and Dimension
132m x 132m square
Mass
134.4 ton
Number of Array module
88
Number of subarray
1936
Number of antenna elements
2,547,776 units
Number of pilot receiver
7,744 units
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4.2 MICROWAVE TRANSMITTER SECTION
The huge amount of solar energy collected by the solar panel in the form of electricity
is to be directed to the earth for the use. This achieved by converting the DC power to
microwave and high frequency microwave transmitter is used to transmit energy to earth.
4.2.1MAGNETRON
A magnetrons is a oscillator used to generate high microwave power. These are crossed
field tubes in which dc electricity and magnetic field are perpendicular to each other.
It consist of a cathode of finite length and radius a at the center surrounded by a
cylindrical anode of radius b. the anode is a slow wave structure consisting of several
reentrant cavities equi-spaced around the circumferences and coupled together through
the anode cathode space by the means of slots. Radial electric field is established by dc
voltage Vo in between the cathode and anode and a dc magnetic flux denoted by Bo is
maintained in positive Z direction by means of permanent magnet.
The electron emitted from the cathode try to travel to anode. but the influence of crossed
field E and H in the space between anode and cathode, it experience force which depends
on it’s velocity. Due to anode cavity in RF noise voltage in the biasing circuit, the RF
field lines are fringed out of the slot to the space. The accelerated electron on the
trajectory , when retarded by this RF field transfer energy from the electron to the cavity
to grow RF oscillations till the system RF loses balances the RF oscillation for stability.
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4.2.2 PHASE CONTROLLED MAGNETRON (PCM)
Phase controlled magnetron is a new magnetron based on high frequency stability
microwave transmitter developed with a magnetron commonly used for home microwave
ovens.
In PCM frequency stabilization is achieved by a frequency locking technique with phase
locked (PLL) feedback.. The RF-DC conversion efficiency of the PCM is much higher
than that of a semiconductor amplifier. Phase of magnetron is controlled with PLL anode
current feedback. The phase of microwave in the developed PCM is achieve by an anode
current feedback as shown in figure.5
4.3 BEAM CONTROL
The most fascinating aspect of wireless power transmission (WPT) is it’s ability to
control the power beam i.e. the microwave beam can be directed to the rectenna on the
earth.
A coded pilot signal from the rectenna towards the SPS ‘s transmitter to provide a phase
reference for a forming and pointing the power beam to from the power beam and point
it back to the rectenna, the phase of the pilot signal captured by receiver located at each
subarray is compared to an board reference frequency distributed equally through
Out the array. If the phase difference exist between the two signals, the received signal
Is phase conjugate and feedback to the phase control circuitry of each dc-RF converter.
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5. Developing of microwave-to-DC-conversion device
(Receiving station)
William C. Brown, working with his colleagues at Raytheon Corporation, was a pioneer
in microwave power transmission. Brown helped develop the rectenna that converts
microwaves to direct (DC) current. Probably the most important element of the project
was that Brown and his fellow engineers solved the critical problem of how to convert
the microwave beam power into the desired DC power out of the receiving antenna.
Brown's solution was the "rectenna" - an assemblage of little dipole antennas connected
to a network of semi-conductor diodes that rectifies, or converts AC to DC power. .He
was first to invent microwave powered helicopter in 1964. Later, studies concerned with
assessing the feasibility of the Solar Power Satellite (SPS) and the High Altitude Powered
Platform (HAPP) found that magnetron power sources and various types of rectennas,
operating at 2.45 GHz, could meet the requirements of microwave power transmission.
Rectenna is composed of a receiving antenna, an input low-pass filter, a rectifying circuit
and an output smoothing filter. the input tilter is needed to suppress re-radiation of high
harmonics that are generated by nonlinear characteristics or the rectifying diode. powerreceiving rectenna arrays--a fine metallic mesh--would be visually transparent.
The other device for back conversion to dc from microwave is a cyclotron wave
converter (CWc). The CWC is a microwave tube device which converts the input
microwave power into dc power. The efficiency of CWC is comparable to or higher than
the world record of the rectenna efficiency(90%) achieved by BROWN only.
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Figure3.2 Schematics of rectenna circuit
In well matched rectenna arrays, An antenna comprising a mesh of dipoles and diodes for
absorbing microwave energy from a transmitter and converting it into electric power. the
diode is the most critical component to achieve high efficiencies because it is the main
source of loss. Schottky barriers diodes utilizing silicon (si),gallium (Ga) and Arsenic
(As) have been employed with rectification efficiencies greater than 80%. The
breakdown voltage (Vbr) limits the diode's power handling capability and is directly
related to the series resistance and junction capacitance through the intrinsic properties of
the diode's material and structure. for instance decreasing the series resistance will
decrease the power dissipated in the diode; however breakdown voltage will decrease or
the junction capacitance will increase. One of the main concerns about rectennas is the
radiation of harmonics generated by the diode. One method of suppressing harmonics is
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by placing a frequency selective surface in front of the rectenna that passes the operating
frequency and attenuates the second and third harmonics. In addition to the filter
rejection a circular patch antenna also serves as a harmonics filter due to its non integer
resonance.
Main idea to use Rectenna in SPS is

To take advantage of microwave power transmission developments associated
with the Solar Power Satellite and High Altitude Powered Platform concepts
and adapt these to Canadian needs.

To investigate the feasibility of using unmanned aircraft powered by
microwave to relay telecommunications signals
Now after the development of idea of rectenna the main problem come into picture is
how would we take high voltage at output from rectenna . This problem is solved by
changing the construction of Rectenna in some extent. For this A prototype dualpolarization micro strip patch rectenna dimensioned for an operating frequency of 8.51
GHz has been built to demonstrate a design concept for obtaining maximum output
voltage from a rectenna of a given size. This rectenna contains nine square micro strip
patch antenna elements in a square array. The antenna can utilize incident radiation with
polarization components parallel to either or both sides of the square because the circuitry
under each patch includes two independent rectifiers — one for each polarization
component. The dc output terminals of the two rectifiers under each patch are connected
in series, and the series rectifier pairs of all patches are connected in series. consequently,
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the maximum output voltage incident radiation) can be 18 times that generated by a
single-rectifier, single-polarization patch element.In tests at an optimized load resistance
of 5.4 k , the rectenna was found to function with an overall energy-conversion efficiency
exceeding 52 percent over a large range of incident power densities, with a peak of 53
percent at a power density of 38.8 mW/cm2. The results of the tests also showed that a
target output potential of 50 Vdc can be achieved at a power density of 25.2 mW/cm2.
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6. Problems and Remedies for setting SPS
Cost inefficiency: The cost of components is the first problem here. Current prices for
solar electric power systems are about $2.50 per peak watt, a price that has been
declining about 7% per year for the last few decades and with continued improvement in
prices in another 10 to 15 years component costs should not be an obstacle to large scale
installation. The other cost of concern is delivery to orbit. Typical communication
satellite solar panels have mass per kw of about 20kg. so with current launch costs of $1
O,OOO/kg that comes to $200/watt or a hundred times too large to be competitive at the
utility level.The NASA/DOE reference design came to IO kg/kw more recent studies of
mass could be as low as Ikg/ kw. Significantly more R&D efforts are required to break
the $2/watt barrier.
There is another way to reduce launch costs. In David Criswell's lunar solar power
proposal instead of launching the final components from Earth ,manufacturing facilities
are sent from Earth to the Moon to build the solar power system components there and to
save even further on launch costs, the solar components stay on the Moon and transmits
power directly from there.
The initial capital investment is higher than for an Earth system primarily due to the
much larger antennas needed to transmit power efficiency from Moon to Earth, but
overall costs per delivered watt should be much lower, and less the costs for such
an approach are less dependent on reducing launch costs from Earth .Further R&D in
robotics may also be needed.
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Health and environment fear: Some fear that a network of solar power satellites
could turn the atmosphere into one big microwave oven, cooking whatever wanders into
the beam's path. In reality, the microwave intensities that we propose would be orders of
magnitude below the threshold at which objects begin to heat up. People would be
exposed to microwave levels comparable to those from microwave ovens and cellular
phones. While some critics speculate that microwaves pose non thermal threats to human
health, there is no reliable epidemiological evidence for adverse effects from microwaves
at these low levels. Higher levels of microwave radiation would be found at the rectennas
on which the beams are focused, but fences and warning signs could demarcate these
areas of possible danger. But according to our calculations, microwave intensities even at
the perimeter of the rectenna would fall within the range now deemed safe by the
Occupational Safety and Health Administration.
Frequency overlap A bigger potential problem is that of sharing the limited
frequencies in the microwave spectrum. Motorola has come under fire, for example,
because its planned system will employ frequencies in the 1.616-to-1.626-gigahertz
range, which almost overlaps the 1.612-gigahertz frequency that astrophysicists tune to
when gathering data about the cosmos. Radio astronomers worry that interference from a
solar power satellite will overwhelm the comparatively weak signals they are seeking to
detect. Motorola promises to limit spillover of its communications beams into the radio
astronomers' frequency niche, but the issue underscores the fact that the microwave
spectrum is a limited resource jealously guarded by commercial and nonprofit users alike.
Allocation of the spectrum must be addressed promptly and effectively to avoid
preemption of space power technology before it's born.
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Market fear: Whether solar power satellites become a reality will ultimately depend
on the willingness of telecommunications and electric utility companies to enter the space
power business. So far, neither industry has shown much interest.
Macauley and Davis surveyed satellite designers and operators, gleaning insight about the
value of having an SSP "power depot" in space. Whisking watts of power through space
to run commercial geostationary satellites looks like a very lucrative and large market,
they report. Macauley said that in future years the space-based power market could be
really big in dollar terms.
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7. Advantages of space power
it is non conventional source of energy.
Enormous amount of energy can be generated by SPS.
Pollution free energy.
Limitless source of energy.
24-hour continuous power generation.
SPS has relatively less land requirement than other energy source.
The technologies like hydro energy, wind energy etc. do not deliver power
continuously, they require some means of storing energy, adding to overall cost and
complexity. A network of solar power satellites in low earth orbit could provide
power to any spot on earth on a virtually continuous basis.
8. Disadvantage of space power
Concept of SPS is too futuristic.
Delivering to orbit is the biggest problem.
The size, complexity, and cost of an SSP undertaking are daunting challenges.
International legal, political, and social acceptability issues abound.
Health or environmental hazards from laser or microwave beams broadcast from
space appear worrisome.
Additionally, in the battle of energy market forces on Earth, any SSP constellation
may prove far too costly to be worth metering.
More R & D and investment in space power project can reduce above demerits to
maximum extends.
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9. CONCLUSION
No single piece of this technology poses a fundamental stumbling block. The physics of
photovoltaic cells and microwave generation are well understood. To move to the next
stage, though will require a demonstration that all the pieces of this system can work
together: the solar panels, the phased-array microwave antennas, the receiving stations
that separate the data signals from the power beams, and the computers that tell the
satellites where on the ground to aim the beams. NASA could accelerate this
development tremendously by placing into orbit a prototype of a solar power satellite.
Considerable progress has been made in the critical area of microwave power
transmission. 5.8 GHz dc-RF converters with efficiencies over 80% are achievable today.
Rectennas developed at 5.8GHz have also been measured with efficiencies greater than
80%with optimized components in both the transmitter and rectenna an SPS system has
the potential of a dc-to-dc efficiency of 45%.The benefits are too large to walk away
from. A network of solar power satellites such as what we propose could supply the earth
with 10 to 30 trillion watts of electrical power - enough to satisfy the needs of the human
race through the next century. Solar power satellites thus offer a vision in which energy
production moves off the earth's surface, allowing everyone to live on a "greener" planet.
Consider the philosophical implications: no longer need humankind see itself trapped on
spaceship earth with limited resources. We could tap the limitless resources of space,
with the planet preserved as a priceless resource of biodiversity.
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7.0 References
 SPACE SOLAR POWER.
HTTP:\\WWW.SPACESOLARPOWER.NASA.GOV.
 HTTP:\\WWW. SPACEFUTURE.COM
 HTTP:\\WWW.SPACE.COM
 P.E. GLASER, ”POWER FROM THE SUN: ITS FUTURE “.
 IEEE MICROWAVE MAGAZINE VOL: 3 NUMBER:4.
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figure 1.0
figure 2.0
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figure 3.0
figure 4.0
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figure 5
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