Abstract:
A portable airborne multi-mission platform designed to collect meteorological data and perform other missions, either alone or in a modular array. Each portable airborne multi-mission platform comprises a tethered aerostat; a hydrogen generation, storage, and recovery system; and a control system. The tethered aerostat consists of an airship, a horizontal axis wind turbine, and a tether cable. The airship is both self-inflating and self-deflating and has the geometry of a wind concentrator and diffuser in fluid communication with the wind turbine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No 13/926,073, filed Jun, 25, 2013. 
     
    
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       FOREIGN PATENT DOCUMENTS 
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       OTHER REFERENCES 
       [0004]    Advisory Circular AC 70/7460-1K “Obstruction Marking and Lighting,” US Department of Transportation/Federal Aviation Administration, February 2007 
         [0005]    Safety Recommendation A-13-016-017, National Transportation Safety Board, May 2013 
         [0006]    Safety Recommendation A-13-018-019, National Transportation Safety Board, May 2013 
         [0007]    NTSB Safety Alert SA-016, “Meteorological Evaluation Towers,” National Transportation Safety Board, March 2011. 
       FIELD OF THE INVENTION 
       [0008]    The present invention relates to the use of a portable tethered aerostat to gather meteorological data, as well as perform other missions including reconnaissance, aerial surveillance or photography, and communications. 
       BACKGROUND OF THE INVENTION 
       [0009]    Currently, nearly all meteorological data is gathered using meteorological masts, that is a portable tower that carries meteorological instruments, typically including equipment to measure the ambient pressure, temperature, wind speed, wind direction, humidity, etc. Typically, such towers are constructed from a lattice structure or long metal pole that is stabilized by guy wires, and are implemented around rocket launch pads, nuclear power stations, and wind farms. Additionally, meteorological masts are used to determine the wind patterns around future wind farms, thereby allowing wind energy developers to accurately estimate the performance of the candidate wind site. In this application, meteorological towers are currently quite attractive due to the ease and speed with which they can be assembled, usually within a few hours. 
         [0010]    However, there recently have been three fatal accidents in the United States during which aircraft collided with meteorological towers and subsequently crashed, killing all occupants. Indeed, meteorological masts pose a significant hazard to aircraft since MET towers can be erected very quickly, and typically, without any notice to the aviation community, creating a significant change to the navigable airspace. Moreover, because most MET masts are less than 200 feet tall, their operators are not usually required by 14 CFR Part 77 to notify the Federal Aviation Administration or to implement a lighting marking plan in accordance with Advisory Circular 70/7460-1K. As a result, pilots have no knowledge of the location of MET towers and have reported difficulty seeing erected MET towers. Finally, it is currently unknown how many MET towers are currently constructed in the United States. 
         [0011]    Recently, the National Transportation Safety Board released six safety recommendation letters to agencies including the Federal Aviation Administration and the American Wind Energy Association requesting changes to documents including AC 70/7460-1 and the Wind Energy Siting Handbook requiring all MET towers to be registered, marked, and lighted. However, the FAA stated that it is not currently considering any further action and that it is impractical to require lighting of MET towers due to their remoteness from pre-existing power sources. 
         [0012]    Therefore, meteorological masts continue to pose a threat to low-altitude aviation operations, including emergency medical services, law enforcement, fish and wildlife surveys, agricultural applications, and aerial fire suppression. Although there have been various innovations addressed toward the field of meteorological observation, such as U.S. Pat. Nos. 8,365,471; 5,646,343; or 8,257,040, hardly any address the hazards that meteorological measurement systems pose to aircraft. Consequently, there exists a need for an alternative method to gather meteorological data without posing a hazard to low-flying aircraft. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention directly addresses the aforementioned problems with prior art, while at the same time possessing greater portability and the ability to perform other missions, such as reconnaissance, surveillance, or communications. 
         [0014]    The present invention comprises a tethered aerostat that houses a horizontal axis wind turbine, a control system that regulates the internal pressure and altitude of the tethered airship, and a hydrogen generation, recovery, and storage system. The tethered aerostat is filled with hydrogen gas so that it is buoyant in the atmosphere and also features the geometry of a high-efficiency concentrator-diffuser wind turbine augmenter, namely a volume of revolution with an airfoil cross-section. The tethered aerostat additionally carries a payload, in the primary instance, a set of meteorological instruments to measure the ambient temperature, barometric pressure, relative humidity, etc. However, the meteorological payload can be substituted with any other payload, such as aerial surveillance or radio telecommunications equipment. 
         [0015]    The present invention is self-powered through the use of the horizontal axis wind turbine, which is mounted in the narrowest cross-section of the airship and is connected to a gearbox that turns an electric generator. The electrical energy generated by the wind turbine is used to power a electrolysis system to generate hydrogen gas, which is used to inflate the tethered airship and stored for future use. During periods of low winds when the wind turbine does not provide sufficient energy to power the control system and payloads, the present invention uses a fuel cell to recombine the stored hydrogen with oxygen to provide the required amount of electrical power. 
         [0016]    The present invention is highly portable since the system additionally recovers the hydrogen used to inflate the airship by activating the hydrogen recovery system, thereby allowing the present invention to be deflated and redeployed without the need for additional lighter-than-air gas to re-inflate the airship, while simultaneously allowing the present invention to continue to power the payload, even during deflation. The present invention also includes a system to prevent damage to the assembly from static discharge and lightning strikes through the use of metallic film coatings, static discharge ports, and grounding wires. 
         [0017]    Finally, the present invention can also be deployed in a modular 2-dimentional or 3-dimentional array, thereby presenting additional advantages, such as the compilation of a 3-dimenionsional map of meteorological conditions in the region of interest or the operation of multiple surveillance or communications systems simultaneously. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0018]      FIG. 1  depicts the tethered aerostat, inflated and tethered to its ground station. 
           [0019]      FIG. 2  depicts the tethered aerostat and its components 
           [0020]      FIG. 3  depicts the front view of the tethered aerostat 
           [0021]      FIG. 4  depicts a half-section view of the airship taken along a vertical plane passing down the axis of symmetry. 
           [0022]      FIG. 5  depicts a half-section view of the airship taken along a horizontal plane passing along the axis of symmetry. 
           [0023]      FIG. 6  depicts the planes along which the sectional view in  FIG. 7  was taken. 
           [0024]      FIG. 7  depicts a ¾ sectional view depicting the internal geometry and components of the airship. 
           [0025]      FIG. 8  depicts the hydrogen generation, storage, and recovery system. 
           [0026]      FIG. 9  depicts the four Y-valves that allow the hydrogen system to switch modes of operation. 
           [0027]      FIG. 10  depicts a winch used to control the length of the tether for the airship. 
           [0028]      FIG. 11  depicts the present invention deployed in a two-dimensional array. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The following description details an exemplary configuration of the present invention that may be embodied in many different geometries, forms, and configurations. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the set of possible configurations of the present invention. 
         [0030]    As depicted in  FIG. 1 , the present invention comprises a tethered aerostat  1 , that is tethered to the ground via a long tether  2 , that is terminated inside the ground station  3 . As depicted in  FIG. 2 , the tethered aerostat comprises a thin-walled envelope  4 , in whose center is mounted a horizontal axis wind turbine  5 . The airship is filled with hydrogen gas so that it is buoyant and supports the weight of the desired payload (not depicted). The geometry of airship is that of a volume of revolution with an airfoil cross-section, causing the airship to function as a wind concentrator-diffuser augmenter. The design consists of a venturi nozzle in fluid communication with a diffuser, such that the wind passing by the aerostat is accelerated through the hole in the airship and over the blades of the wind turbine. Preferably, the airship features an optimized geometry to maximize the airflow through the center of the blimp; such a geometry can be determined by either empirical or numerical analysis techniques. The airship is preferably tethered with at least three tethers  7  that are joined into a single central tether  8  to help equally distribute the aerodynamic loads between the airship and the central tether. The airship is directed into the oncoming wind direction by the combination of a larger surface area of diffuser portion of the airship and the stabilizing fins  6 . 
         [0031]    The airship envelope  4  is preferably made of a resilient flexible material or set of materials so as to minimize effusion of the hydrogen gas from the assembly. The assembly could use a thin polymer film (such as polyethylene, Mylar®, or any other similar material) to maintain the pressure of the assembly while using a high-strength woven fiber (Dacron®, Vectran®, Spectra®, Kevlar®, carbon fiber, or any other material suitable for the application) to maintain the shape of the shroud. Additionally, the inflated components could be coated with a UV resistant and/or abrasion resistant coating, such as Tedlar® to ensure the desired level of strength to maximize the lifetime of the present invention. 
         [0032]    The airship may also include a lightweight, collapsible internal structure, such as ribs, stringers, or other similar frame to help the airship maintain its geometry during turbulent winds. The internal structure would be preferably manufactured from a lightweight composite material, such as a plastic reinforced with carbon fiber, fiberglass, Kevlar®, Spectra®, or any other suitable material. However, it is important to recognize that the structural details described above are not limiting, but a guideline for those skilled in the art to understanding the nature of the present invention. 
         [0033]    Additionally, to minimize the risk of accidents caused by static electricity or lightning strikes, the internal and external surfaces of the shroud are coated with a thin metallic film, such as that commonly used in the electronics industry to protect integrated circuits from static discharge. The metallic films could also be supplemented by a conductive metallic mesh or foil, such as is used in the aircraft industry to protect composite aircraft from lightning strikes. The metallic films and/or meshes would then be connected to a ground wire and static discharge ports  11 . The static discharge ports  11  would also serve to protect the system from lightning strikes by providing a discharge path around the important components of the system. 
         [0034]    Finally, the airship and its tethers incorporate obstruction marking and lighting in accordance with Chapter 11 of Advisory Circular AC 70/7460-1K to help minimize the hazards posed to aircraft. As depicted in  FIGS. 2 and 7 , flashing red or white obstruction lights  9  are placed on the leading and trailing edges of the airship, as well as along the length of the tether, spaced in equal intervals. Additionally, the airship tether includes stiffened flags  10  spaced along the length of the tether to increase the visibility of the airship during the daytime. 
         [0035]    As depicted in  FIG. 4 , the airship envelope includes an outer surface  13  and an inner surface  14 . The volume  15  bounded between the two envelopes is filled with hydrogen gas that is generated in the ground station and delivered to the airship via the tether. The horizontal axis wind turbine  5  is mounted in the narrowest section of the inner surface of the envelope  14 , thereby increasing the speed of the wind passing over the blades of the wind turbine, and thus maximizing the efficiency of the wind turbine. The wind turbine  5  is connected to a gearbox and electrical generator  12 , thereby converting the available mechanical energy of the wind into electrical energy to power the airship and its payload. The electrical generator  12  may be synchronous or asynchronous AC 1-phase or 3-phase, DC, or any suitable electrical generator, as desired by the designer. However, a DC generator is preferred since most electronics, especially hydrogen electrolysis units, operate off of direct current; using a direct current electric generator would thereby eliminate the need for an inverter, hence reducing the size, weight, and cost of the present invention. 
         [0036]      FIG. 5  depicts the one of the possible support structures that could be used to constrain the wind turbine and the electric generator within the airship. One possible support structure is the use of three lightweight ropes  16 , manufactured of a lightweight fiber or other suitable material. When the assembly is fully inflated, the inners surface  14  of the airship envelop would pull the ropes  16  taut, thereby suspending the turbine in the throat of the airship. However, there are many other possible support structures not depicted, such as the use of a housing and supporting rods that are fastened to the internal stiffening structure or any other suitable method of constraining the wind turbine within the center of the airship. In no way are the designs discussed here intended to be limiting of the shape, reinforcements, or any other aspect of the design of the inflatable aerostat, but to give the designer an understanding of the present invention. 
         [0037]      FIG. 7  depicts a three-quarter section view of the tethered aerostat, depicting the aforementioned components of the airship, including the inner and outer surfaces of the airship envelope  13  and  14 , the wind turbine  5  and electric generator  12 , the static discharge ports  11 , and one of the obstruction lights  9  spaced along the tether. 
         [0038]      FIG. 8  depicts the hydrogen generation, recovery, and storage system, which is used to inflate the tethered aerostat and store energy for future use by the payloads. The system comprises a condenser  17 , a hydrogen electrolysis unit  20 , a compressor  24 , a fuel cell  29 , a hydrogen gas storage tank  37 , and Y-valves  26 ,  27 ,  32 , and  33 . 
         [0039]    The present invention stores the electrical energy generated by the wind turbine by converting it to hydrogen as described herein. The wind turbine supplies electrical power to the condenser  17 , which condenses the water vapor from the surrounding atmosphere, through the electrical leads  18 . The condenser then pumps the condensed water into the electrolysis unit  20  through a water line  19 . The electrolysis unit also receives electrical power from the wind turbine through wires  22  that are connected to the electrodes inside the unit, which decompose the water generated by the condenser in hydrogen and oxygen. The oxygen gas is exhausted from the unit through line  21 , where it is either vented into the atmosphere or supplied to some other system, such as breathing oxygen, compression and storage in a tank, or any other system desired by the designer or consumer. The hydrogen then passes through line  23 , where it is compressed by the compressor  24  to a higher pressure. As depicted in  FIGS. 9 and 10 , the hydrogen gas exits through line  25 , after which it is directed by Y-valves  25  and  27  into line  31 , which fills the hydrogen storage tank  37 . 
         [0040]    The hydrogen generation, storage, and recovery system is also operated by a feedback control system to regulate the pressure of the hydrogen gas contained within the airship envelope. The feedback system would monitor the pressure of the hydrogen gas using a pressure transducer or other appropriate device that would supply data concerning the gas pressure to the control system. When the internal pressure would fall below some predetermined minimum level, the control system would activate the condenser, electrolysis unit, and the compressor, which would operate as described before. However, Y-valves  26 ,  32 , and  33  direct the compressed hydrogen gas into line  36 , which is later integrated into the tether, which delivers the compressed hydrogen gas to the airship, re-inflating it to the required pressure. Conversely, if the internal pressure were to rise above a maximum value, the control system would, rather than venting the gas into the atmosphere, would switch Y-valves  32  so that the compressor would draw in hydrogen from line  35 , thereby deflating the airship, and then pump the hydrogen gas into the storage tank for future use. 
         [0041]    The hydrogen system can also power the control system and payloads during periods of low winds when the wind turbine is unable to produce sufficient power for the system. During such times, Y-valve  27  would switch so that the hydrogen storage tank  37  would supply hydrogen gas to the fuel cell  29 , which would generate sufficient electricity to power the payloads. 
         [0042]    Additionally, the hydrogen storage tank could be used to re-inflate the wind turbine by switching Y-valve  33  to allow hydrogen gas to exit the storage tank through line  34 , after which it would pass into line  36 , and then into the airship. 
         [0043]    Furthermore, the hydrogen system allows the airship to be deflated without loss of the hydrogen gas that was used to inflate the airship by switching Y-valve  32 , thereby allowing the compressor to pump all the hydrogen gas out of the airship and into the storage tank. The airship could then be easily folded and packed for transportation to another site. The aerostat, after arriving at its new destination could then be re-inflated with the hydrogen stored in the hydrogen storage tank. 
         [0044]    As depicted in  FIG. 10 , the length of the tether is regulated by a winch or drum-type mechanism located in the ground station that comprises the drum and its supporting frame  38 , a motor to turn the drum  41 , which is powered by the control system through electrical leads  42 . The tether  8  is wrapped around the drum, so that the aerostat can raised and lowered by extending or retracting the tether line. Finally, the tether line  8  consists of at least  3  internal lines, namely the hydrogen supply line  36 , the electrical leads from the wind turbine  39 , and the data cables for the control system and payload  40 . 
         [0045]    The entire assembly is controlled using a control system (not depicted) that controls the pressure of the hydrogen gas inside the blimp and the altitude of the blimp, as described herein. The control system includes, but is not limited to, the aforementioned feedback system to control the pressure of the hydrogen gas, a feedback control system to control the rotational speed of the wind turbine rotor, and a feedfoward control system that would protect the blimp from severe weather. The second feedback control system would control the altitude of the wind turbine and ensure that the wind turbine rotor does not reach excessive rotational speeds that could damage the assembly. The control system would feature a device to measure the altitude of the airship, preferably a GPS receiver, and another device to measure the angular velocity of the turbine blades and relay that information to the control system. Initially the control system would let the blimp rise until it reached the desired altitude, and then lock the mechanism controlling the length of the tethers. However, if the wind turbine rotor was to reach a predetermined maximum angular speed, the control system would decrease the length of the tether until the blimp reached an altitude with a sufficiently low wind speed, thus protecting the wind turbine and airship from structural damage. 
         [0046]    Lastly, the third control system features a feedfoward system that would be activated by the operator to retract the airship to ground level in case of severe weather aloft, thus protecting the system from damage that it could have encountered at high altitudes. However, if severe weather is expected at both altitude and ground level, the user-activated feedfoward control system would also deflate the airship using the hydrogen recovery system that was described earlier, thus minimizing any possible damage to the portable airborne multi-mission platform. 
         [0047]    The present invention can be used for a variety of applications, including meteorology, reconnaissance, surveillance, or radio telecommunications. In the primary instance, the meteorological data collection payload would typically include instruments for measuring the temperature, pressure, humidity, etc. However, due to the innovative design of the tethered aerostat, the use of a conventional wind meter to determine the wind speed and direction is not necessary. The present invention would determine the wind speed of the air passing by the tethered aerostat by measuring the power output and/or the rotational speed of the horizontal axis wind turbine, and then using an algorithm to determine the wind speed via a calibration curve developed for the aerostat system. Likewise, since the airship self-orients into the oncoming wind direction and will always be slightly downwind of the ground station, the system would determine the wind direction by comparing the location of the airship, as preferably determined by a GPS receiver, with the coordinates of the ground station. In other embodiments, the present invention would serve as a portable, versatile platform for other payloads including high resolution cameras, radio transmitters and receivers, or any other desired payload. 
         [0048]    Finally, as depicted in  FIG. 11 , the tethered airships may be arranged in a two-dimensional or three-dimensional array. In the primary application of gathering meteorological data, deployment of the present invention in an array allows the operator to gather information and generate a two-dimensional or even three-dimensional grid of meteorological data, which can serve to help predict the future meteorological conditions for the region of interest with far greater accuracy than a single deployment of the present invention. For other applications, a plurality of airships can serve to provide surveillance of multiple regions simultaneously, allow improved performance of a radio communications by creating an array of radio transmitters, etc.