Solar Powered Satellite System

Solar Powered Satellite (SPS) System By Subhasis Paul

Introduction

In the interest of all, particularly school going students, this narration on SPS and ushering of new Space Age has focused on the basic principles of science that forms the foundation of this program. Alternate source of energy have always enthused us. Projects on domestic lighting using solar energy are now done at school level. Commercializations from steam engine to computer and internet have led to far reaching social consequences. When operational, SPS will have similar rippling effect all across the globe. This awareness on SPS will be beneficial for students, parents and teachers to understand the complex geo political world awaiting us in near future. The SPS phenomena will draw interest not only from scientists and engineers but also followers from other disciplines like finance and arts. For me, this is a new subject. I am greatly influenced by my college friend Dr.S.Sen to trigger this special interest in me.

Terms Planetary Orbit: It is the path traced by planets in its journey around the sun. Earth rotates around sun and thus avoids collision with sun due to each others gravitational attraction. The inward gravitational force on earth is neutralized by outward centripetal force that arises due to earth’s rotation around sun. Imagine a chord, tied to a rotating stone at one end snaps suddenly. The stone will rocket outward from the centre of rotation. The force that causes this outward motion is centripetal force. This is the underlying principle of rotation of planets around the sun or man made satellites around earth.

FC

E

FG FG

Sun

Earth Orbit

Geostationary Orbit (GEO): Earth rotates about an axis passing through north and south pole that causes day and night. The period of rotation is 1 day or 24 hours. Imagine a satellite rotating around earth with the same time period. A light beam focused from the satellite always falls on the same place on earth. The satellite will appear stationary with respect to a fixed point on rotating earth. This happens at no expense of energy. The orbit at which this phenomenon happens is called GEO. The orbit distance from earth’s surface can be mathematically calculated. The distance is independent of the weight of the satellite. GEO is about 35800 Km from earth surface at equator. Most commercial communications satellites, broadcast satellites and meteorological satellites operate in geostationary orbit. Low Earth Orbit (LEO): Whereas GEO is at 35800 Km, LEO is the space within 2000 Km from earth surface. For SPS system, LEO has been conceived to play the role of final launching pad to GEO. Crew strength required for construction and maintenance for SPS can be based at LEO. Introduction of LEO in SPS system also improves the economy of the system. Current SPS system design estimates LEO to be at 500 Km from earth surface. EM Spectrum: Spectrum means range, variety. Start with light, the most visible Electromagnetic wave. Light is a form of energy. The EM wave that we observe is the physical manifestation of this energy. The range and variety of physical manifestation of energy is known as EM Spectrum. Some of the physical measurements of EM wave are temperature, human visibility, atmospheric penetrability, wave length or frequency. Wave speed is always constant and equals speed of light. Some of the nomenclatures of these energy levels are familiar to us – radio wave, microwave, X-ray. All are energy, manifested in infinite probability.

Photon: Photons are the carriers of energy. It carries energy of all EM waves - gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. It has zero mass and travels at the speed of light. Energy of photon is proportional to its frequency. Thus an infrared-photon carries less energy than a visible-photon. Microwave: Microwaves are EM waves at certain frequency span of EM spectrum. Microwaves are extensively used for communication, remote sensing and navigation. For power transmission from SPS to Earth, MW technology can be used. Quantum Mechanics: The physical universe is probabilistic rather than deterministic. So is the underlying principal of quantum mechanics. Quantum mechanics is the study of mechanical systems whose dimensions are close to or below the atomic scale, such as molecules, atoms, electrons, protons and other subatomic particles. Without it, the theory of Planetary Orbit as explained above with classical mechanics cannot be applied to the constantly orbiting electrons around an atomic nucleus. For example, if classical Newtonian mechanics governed the workings of an atom, electrons would rapidly travel towards and collide with the nucleus, making stable atoms impossible. One of the main pillars of Quantum theory is Heisenberg' s uncertainty principle. It states that the location of an orbiting electron around nucleus cannot be precisely determined. Quantum theory also postulates that elementary particles behave both like particle and like waves. Photovoltaic (PV): PV is a technique that converts light energy to electrical energy. Quantum mechanics can explain the photovoltaic effect i.e. why a ray of light or photon, incident on certain materials can release a free electron and thus produce electricity. There is no moving part involved in this type of electricity generation, thus reducing maintenance. Nanotechnology: Nano means 10-9. One nanometer is 10-9 meter. Nanotechnology is the branch of science and engineering that deals with matter at nanometer scale. At nano-scale, quantum forces become the dominating force over gravity resulting in change of some physical properties (mechanical, electrical, optical etc.) of the matter. Using the concept of molecular manufacturing, materials can be built using nano-machines to satisfy some predetermined requirements. Nanotechnology can play a significant role in manufacturing high efficient solar cells that produce electricity from sun light.

Concept The concept of SPS was patented in US by Peter Glaster in 1973. Since then it arose interest at various time and across many state and non-state organizations. NASA is one of the main proponents of SPS system.

Geostationary Orbit

Transmitting Antenna - always oriented towards fixed receiving antenna on earth

Receiving antenna on earth

Satellite

Sunlight Collector cells always oriented towards Sun

The basic concept is to put a satellite in space to capture continuous solar energy and beam the energy back to earth. The satellite will be placed in geostationary orbit so that energy beam from the transmitting antenna of the satellite is always directed towards the fixed receiving antenna on earth. With this configuration, three distinct possibilities exist to beam back energy from sun and harness it on earth. Solar Dynamic (SD): SD uses a heat engine to drive a piston or a turbine which connects to a generator or dynamo to produce electricity. At the receiving end, it is very similar to a coal or gas fired power plant with the exception that instead of coal or gas, the heat is provided by highly concentrated sunlight. The transmitting end will have large curved reflectors to focus sunlight to achieve a high temperature for the heat engine to operate at high thermodynamic efficiency. This will possibly be done using Laser technology. The reflecting mirrors can be made from very this aluminum or other metal sheets with very light frames, easily constructed from materials available in space (eg, on the Moon' s surface). Photovoltaic (PV): PV uses collector cells installed at satellite end that are photovoltaic in nature. These cells convert sunlight or photons to electricity via a quantum mechanical mechanism. These are commonly known as “solar cells”, and will likely be quite different from the glass panel protected solar cell panels familiar to us. Electricity thus generated is converted to directed microwave and beamed on earth surface using transmitting antenna. On earth, MW is converted back to electricity. Concentrating Photovoltaic (CPV): CPV system like SD use large mirror arrays in space to beam back concentrated light to earth. On earth PV technology is used to convert concentrated light to electricity, thus avoiding thermodynamic constraints which apply to heat engines.

SPS Design We will discuss here the Original SPS Reference Design as envisioned by NASA with the current set of technology and knowledge base we have. The design takes into consideration technology options, finance and economy of power utility, international relations and the global environmental situations. The figures below will reiterate the gigantic tasks that lay ahead of us. Satellite System Overall Dimension Structural Material GEO Distance LEO Distance Collection System DC to MW Conversion Transmission Antenna Diameter

10 x 5 x 0.5 Km Graphite composite 35800 Km 480 Km PV cells Klystron machine 1 Km

Earth System Output Power of Each Unit Receiving Antenna Size MW to Electricity Conversion (DC) DC to AC Conversion

5GW (5 x 109 Watt) 12 x 15 Km

Sun Ray

PV Collector System

Klystron System

DC

Guided MW Directed MW

Directed MW

Transmitting Antenna System

Receiving Antenna System Guided MW

MW to DC Converter

Electricity

Efficiency of SPS SPS System requires conversion of energy from one form to other. In an ideal world, energy cannot be created or destroyed. But for SPS as an isolated system each conversion will be accompanied by an energy conversion loss. Less the loss, more is the efficiency. In addition there are other losses during sun energy collection and transmission. These are the conversion processes and efficiency percentage for a PV Type SPS System: Conversion Process

Efficiency %

Comment

PV Collection Conversion of Photons to Electricity Conversion of Electricity to Microwave Antenna Collection Wireless Transmission Loss Antenna Collection Conversion of MW to Electricity

88 15.7 76.6 96.5 96.1 78.3

At transmission end Very low, at transmission end Mechanized, at transmission end At transmission end In space and earth atmosphere On Earth Mechanized, on Earth

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Overall efficiency of the SPS System is 7.81% (= product of efficiency of each constituent systems). One area of improvement is item#2, conversion of photon to electricity. We understand that this conversion can be well explained by quantum mechanics. Advancement of our knowledge in nanotechnology coupled with that of quantum mechanics will lead to development of very high efficient PV cells, thereby enhancing the overall efficiency of SPS System. The other energy conversion areas, electricity to microwave and vice versa are done by man made machines and also have potential for improvements.

Advantages of SPS • • • • •

The lifetime of the sun is an estimated 4-5 billion years, making space solar power a truly longterm energy solution. Unlike oil, gas, ethanol, and coal plants, space solar power does not emit greenhouse gases or depend on increasingly scarce fresh water or mineral resources on earth. It does not require environmentally problematic mining operations. Unlike nuclear power plants, space solar power will not produce hazardous waste, which needs to be stored and guarded for hundreds of years. Unlike earth based solar and wind power plants, space solar power is available 24 hours a day, 7 days a week, in huge quantities. It works regardless of cloud cover, daylight, or wind speed. Space solar power will not require dependence on unstable or hostile foreign oil providers to meet energy needs, thereby eliminating a major source of national competition for limited Earth-based energy resources.

Time Span and Commercial Viability In the concept of Design to Cost, it is assumed that the retail price of the end product is known. Accordingly production cost of each component is derived. The retail cost of electricity from SPS has to be pragmatically calculated taking into consideration future cost rise of electricity generated from conventional technologies. Constant R&D will bring down production and implementation cost of each of the SPS components. Infusion of new technology frontiers like nanotechnology will further narrow down the design and calculated cost gap. Time span to make SPS system operational is related to its commercial viability.

COST CONVENTIONAL

SPS

TIME

Problem Areas Mankind has never before built anything on Earth or Space as colossal as this. There are innumerable risks. There are risks involved with the required speed of technological advancements, construction problems, transportation hazards, safety hazards and financial concerns. But then all projects start with high risk and tend to become green as the project progresses. For now, the project is a non-starter as with all optimizations, the power generation cost is prohibitively high, about eight to ten times of current electricity cost. Generation of electricity by SPS and thereby dependency reduction on fossil fuel will also demand development in other areas like transportation systems. With the development of hybrid car that runs on rechargeable batteries, the purpose is lost if the batteries are required to be charged from electricity generated with fossil fuel.

Conclusion SPS will bring great change in foreign relations. There will be excellent advancement of energy security – the dependence on imported oil. With improved energy security, relation between nations will be redefined. China, for example, will no longer need to prop up unstable states like Sudan and Venezuela. India will put her grand oil pipeline plan from Iran via disturbed territories of Pakistan in cold storage. Europe’s dependency on state owned Russian oil will lessen. It will spell doom for programs like the infamous Oil for Food of Iraq. The geo political reverberations of an operational SPS system will be global. Nations eager to achieve this security and further their development goals need to join hands and commit resources in SPS project, the size and scope of which will rival that of Manhattan project, unleashed by U.S. for development of nuclear bomb.

Sources Wikipedia Encyclopedia - http://en.wikipedia.org/wiki/Solar_power_satellite Space Solar Power Library - http://www.nss.org/settlement/ssp/library/index.htm SPS Reference Design - http://fti.neep.wisc.edu/neep533/SPRING2004/lecture40.pdf Solar Photovoltaic Technologies - http://www.dep.iitb.ac.in/SPT/slides/Lecture-2%20SPT-DEC.ppt#1 Centre for Responsible Nanotechnology (CRN) - http://www.crnano.org/