BACKGROUND
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The transmission of energy from a solar collector/converter in space to a ground-based distribution system is accomplished by converting the solar energy to electricity which drives a generator of electromagnetic radiation. The radiation propagates in the rarified medium of space as a beam focused upon a receiving transducer. This is called the “Wireless Power Transmission (WPT).” If the receiving transducer is located on the ground, then the WPT must travel through the Earth's atmosphere to get to the receiver. The receiving transducer converts the radiation into electromotive force and current that feeds into an electrical power distribution system. One problem with this arrangement is that losses occur during WPT because constituents of the Earth's atmosphere scatter, reflect, and absorb the energy of the transmission.
SYSTEM INVENTION DESCRIPTION
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Given the scenario described in the above paragraph, elevating the target transducer above the ground lessens the distance that the WPT must travel through lossy atmosphere, and thereby reduces the total lost energy. In this invention, a system is constructed to elevate a target transducer that receives energy beamed to it from a space-based solar energy collector/converter.
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When the target transducer is elevated, a conduit containing a conductive transmission line (CTL) which may be constructed with a series of conductive cable elements, trails below the transducer to the ground-based power distribution system. The CTL provides a low loss path for induced electrical current to flow from the transducer to the ground-based power distribution system. In this invention, the transducer and the segments of the CTL are attached to vessels which are buoyant in Earth's atmosphere (see FIG. 1). Each of the multiple buoyant vessels (typically called “balloons” and filled with helium, hydrogen, or hot air) supports the CTL and is firmly attached to it so that if the CTL moves, the vessel attachment moves with the CTL to an extent that will keep the placement of each vessel along the CTL within design tolerances. Each vessel is designed to support the weight of the CTL below it and bear it to a predetermined nominal height. The lower balloons can bear more weight than the higher ones because of the increased density at lower altitudes. Thus, the vessel design will utilize a mathematical model and/or measurements of the atmospheric density applicable to the region of deployment. The size of the vessels, and the amount of buoyant gas that each holds will depend upon the atmospheric density as a function of altitude as was mentioned previously. The size of the vessels, and the amount of buoyant gas that each holds, will depend upon the expected atmospheric density according to where they are to be positioned vertically in the system.
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Unmanned helium-filled balloons have achieved altitudes of approximately 30 miles (˜50 km). In this invention, the gas-filled vessels are designed to be large enough to bear the weight of the CTL, as described above, and collectively achieve the result that the receiving transducer is borne to an altitude that is above much of the worst interference that the chosen frequency(s) of the WPT would encounter. If the transducer is borne to an altitude above the troposphere (-18 km), then it will be above most of the weather, and significant reduction of propagation losses can be achieved in some important electromagnetic frequency bands. FIG. 1 contains a graphical depiction of a realization of this system.
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Buoyancy vessels (or clusters of them if buoyancy requirements so dictate) are spaced on the CTL in such a way as to bear the CTL weight and relieve the transducer carrier from excess burden that would limit the transducer carrier's altitude to a less than the preferable level, given the spectral content of the WPT. Depending upon the materials and shapes used in the buoyancy vessels, the receiving transducer is mounted in a position that will be targeted by the transmitter without experiencing interference in the transmission due to the vessel. The position indicated in FIG. 1 is not necessarily required. For instance, the transducer could be hanging below the transducer carrier vessel.
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It is preferable that the system be deployed by releasing the vessel that will be farthest from the ground first, and then releasing each consecutively lower vessel in turn. The vessels are adjusted to reach a predetermined height and/or predetermined increment of height over the adjacent lower vessel. This increment may be less than the length of the segment of the CTL hanging off of the next higher vessel, leaving slack in the segment. Slack in the CTL helps to decouple the motion of one vessel from another. Stiffness of the CTL, augmented by attached stiffeners if necessary, will tend to hold it away from the vessels. The buoyancy presets that are used at the time of launching/raising may be based upon a model and/or measurement of the atmospheric density gradient as a function of height (see equations 1, 2, and 3). There are two different equations for estimating pressure at various height regimes below 86 km (or 278,400 feet). Equation 1 (See Drawings) is used when the value of standard temperature lapse rate is not equal to zero and equation 2 (See Drawings) is used when standard temperature lapse rate equals zero.
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The buoyancy or lifting force produced by a vessel is equal to the weight of the air displaced by vessel minus the weight of the vessel and the gas within it. So, given the density of the air spanning the extent of the vessel at various heights, one can calculate an estimate of the buoyancies of a vessel when it is at various heights. When a vessel reaches a height where the lifting force is equal to the load on the vessel, the vessel will cease to rise through the atmosphere. The volume of gas filler for each vessel may be calculated from this condition: the volume must be such that the lifting force equals the weight of the vessel's load when the atmospheric density is equal to that expected at the design height of the vessel in the system. If the available vessels do not have the required capacity, then they must be replaced with ones that do, or the system must be redesigned to not require the excessive vessel capacity.
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The load on each vessel may be estimated using a simple model of the shape of the CTL between vessels (see FIG. 3 and equation 4) and the linear density, in kilograms per meter of length, of the CTL. In this model, half the weight of the arc is borne by the next lower vessel. Using this model, the load on a vessel will be given by the equation within the attached drawings.
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Given the spectral characteristics of the WPT, a target height for the WPT receiver can be proposed based on atmospheric transmission characteristics as are depicted in FIG. 4. The proposed receiver height, the atmospheric model (as above), and the load weight, WN (defined below), may in turn be used to determine the topmost vessel displacement. Of course, this determination would also factor in the type of gas filler that is to be used and the temperatures involved.
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Given a calculated volume of gas filler to achieve load buoyancy at prescribed heights for each vessel, they may each be given an appropriate fill before launch. Each vessel contains a mechanism for controlled release or infusion of gas that can be actuated remotely. In addition to the conductor, the CTL structure may include tubes for replenishing gas within the vessels by pumping it from a reservoir on the ground through the tubes and into the vessels. Thus, after all the vessels have deployed to their stable heights, adjustment of their heights is made by releasing/infusing gas into the vessels. This adjustment starts with the highest vessel and proceeds to the next highest consecutively all the way down through the vessels until the lowest vessel is adjusted. These mechanisms can also be used to compensate for vessel leakage or other deleterious effects upon the buoyancies.
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Possible influences:
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- Wind will tend to distribute the system more horizontally and concurrently lower the elevation of upper vessels which bear the transducer. The response to wind will depend upon the characteristics (e.g., weight and stiffness) of the CTL, and also upon the characteristics of the buoyant vessels. Slack in the CTL just above each of the vessels (forming an arc below the connection to each vessel as depicted in FIGS. 1 and 2) provides some decoupling of the upper portions of the CTL from motion in the lower portions.
- The solar array system will contain an electromagnetic transmission device, the efficacy of which will depend upon the operating frequency of the particular device chosen. Planning of overall performance will entail the use of an atmospheric spectral transmission model. FIG. 4 shows relative propagation efficacy for various wavelengths. Mid-range microwaves will propagate well through the ionosphere, down to near the level of the top of the troposphere (˜18 km) and wireless power transmission (WPT) using microwaves has already been developed and demonstrated. Thus, a high-power microwave device is a good choice for the transmitter on the solar array platform if the device can be made sufficiently lightweight and compact. One of the advantages of using the buoyancy-borne transmission system described in this invention is that it allows the use of the higher frequency transmission with higher power and less spreading and diffraction in the beam. Another advantage is that it puts the receiving transducer closer to the sender, making it easier to focus the beam on the transducer.
- If the vessels cannot be adjusted to operational heights, then this is likely a failure of the atmospheric model and the vessels must be filled with additional gas using the data from the attempt. If additional gas will not solve the problem, then the vessels, transducer, or CTL need to be redesigned.
BENEFITS
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It is expected that use of this system will greatly reduce transmission losses incurred by space-borne (e.g., orbiting) solar power converter platforms sending power to ground-based power distribution systems. These platforms can potentially collect and convert solar energy continuously because they can be placed where they are never in the shadow of the planet Earth (e.g., in a polar orbit).
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FIG. 2 depicts the entire scenario of (1) collection of solar power, (2) electromagnetic transmission of power to the transducer, and (3) transmission of power via CTL to the ground-based power distribution system. Several elevated transducers may be distributed geographically so that the collector can target the one which is least affected by weather or other deleterious circumstance.
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While the present invention has been described in terms of specific embodiments, it is to be understood that the invention is not limited to these disclosed embodiments. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of illustration only and so that this disclosure will be thorough, complete and will fully convey the full scope of the invention to those skilled in the art. Indeed, many modifications and other embodiments of the invention will come to mind of those skilled in the art to which this invention pertains, and which are intended to be and are covered by both this disclosure, the drawings and the claims.
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A brief description of the included equations and figures is hereby rendered. Equations 1 and 2 are mathematical expressions for the static pressure in the atmosphere. Definitions for associated variables are supplied with the equations. The values for b and hb can be taken from the table 1. For example, at a height above 20,000 m and below 32,000 m, b equals 2 and hb equals 20,000.
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Equation 3 is an expression for the weight borne by the ith topmost buoyant vessel, and is referred to in the above specification. Definitions for the variables are given.
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FIG. 1 is a drawing that graphically depicts a potential arrangement of the buoyant vessels attached to the transmission cable. The vessels are distributed along the cable at appropriate heights.
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FIG. 2 graphically depicts the relationship of the system to a realistic height for the cloud layer and also a realistic height for the solar array with transmitter. The system is shown in-situ, with the electromagnetic transmission from the solar array to the receiver depicted as a white line.
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FIG. 3 shows a simple model for the shape of a CTL segment. The shape is modeled as a vertical drop and a circular arc. Half the weight of the arc is borne by the next lower vessel.
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FIG. 4 depicts the attenuation of various wavelengths of electromagnetic energy (under ideal conditions) as it passes through the atmosphere. The white, purple, and blue areas along the bottom of the graph indicate elevations and frequency regimes where readiation is absorbed most strongly by the atmosphere by increasing degree in that order. In many of the atmospheric conditions that may actually occur, even the visible part of the spectrum can often be attenuated by 20-40% when passing through the atmosphere. The frequency regimes are, from left to right: Radio (orange), Microwave (gold), Infrared (pink), Visible Light (yellow), UV (green), X-rays (blue), and Gamma Rays (purple).
