In February , Airbus received from the UK Ministry of Defence a request for the production and operation of 2 Zephyr S, worth 13 million pounds about 18 million dollars , with flights scheduled to Airbus ; Stevenson This is the first contract in the world for providing an operational HAP. The objective of the US Army High Altitude Airship HAA Program, initiated in , was to develop an operating system based on a high-altitude airship, able to carry a payload on the order of to 1, kg to an altitude of 20 km for months.
The demonstrator had a length of 73 m, a total mass of 1, kg and a payload of 36 kg. It was designed to maintain a flight at 18 km altitude for 2 weeks. In this flight, the airship did not exceed the altitude of 10 km. It was noticed a decrease in the rate of climb, which could take the airship to leave the restricted area defined by the American air traffic control agency Federal Aviation Administration — FAA.
It was decided to command an emergency recovery, with release of the helium gas. The aircraft descended on trees, after 2 hours and 40 minutes of flight. During the recovery operation, after removal of most of the equipment, a short circuit in solar panels caused a fire, destroying the aircraft. No person was injured due to the accident. After the accident analysis, it was verified that the rate of climb decrease was caused by freezing in the air valve. The program was terminated in , with no provision for allocation of new DoD resources DoD Despite the accident, caused by a subsystem failure, the work carried out indicates that it is very likely that the HALE-D Project will be successful in case it is resumed Androulakakis and Judy Lockheed Martin was the prime contractor for the airship development and Raytheon, for the radar development DoD In its demonstration version, the airship would have a length of m, a total mass of 15, kg and a payload of 1, kg, capable of flying at the altitude of 20 km for one year.
In the final version Fig.papacrocodil.ru/includes/2019-03-13/120-muzhchina-vesi.php
The program was restructured in , starting to focus on development risk reduction activities for radar and airship envelope materials. The Very high altitude, Ultra endurance, Loitering Theatre Unmanned Reconnaissance Element Vulture Program, coordinated by DARPA, had the purpose of developing a high-altitude airplane with ability to remain in flight for 5 years, with a payload of kg, which consume 5kW.
The first phase of the program began in with conceptual studies and duration of 12 months. Three companies were contracted for this phase: The second phase Risk Reduction Demonstration — RRD started in and included the construction of a subscale vehicle, including demonstration of a flight with 3 months duration.
Three companies submitted solar planes proposals for the second phase Fig. The Odysseus, proposed by Aurora, presented an innovative concept. Three aircraft, each with 49 m wingspan, would take off separately and would be jointed, by the wing tip, to form a single aircraft at high altitude. During the day the aircraft would take the Z form to maximize the solar energy capture. At night, the wing would be set to a straight form to minimize aerodynamic drag.
Boeing was the winner to perform the second phase, with the m wingspan SolarEagle, in a contract of 89 million dollars. The first flight was planned to IHS ; Boeing Proposals for Phase 2: In , the Vulture Program was restructured, with the SolarEagle development being stopped and going to focus only on technologies for solar energy Photovoltaic Cells and energy storage RFC Defense Daily The operating altitude is 20 km, in one-year flight periods, limited by maintenance stops, which includes lifting gas replenishment Thales Alenia Space a.
The StratoBus design incorporates some innovative solutions such as the use of a transparent envelope section that allows sunlight reflection in concentrators mirrors directed to solar panels inside the airship Thales Alenia Space patent. This allows a reduction in the size and weight of the solar panels and also protects the solar cells from the degradation caused by the stratospheric environment. Another innovation is the use of a large ring fixing the engines and the equipment gondola, allowing the airship to rotate for better sunlight harness.
The Thales Alenia Space planning is of 2 years for development of key technologies, such as the envelope material and the RFC, 2 years to build the first prototype and one year for flight tests. The forecast is that the product may be offered to the market after Thales Alenia Space In April , the project received an investment of 17 million euros about 19 million dollars from the French government for the 2-year key technologies development phase. A demonstrator flight is scheduled for Thales Alenia Space b.
High-altitude platform station
Project Loon, from Google, started in and has the objective to create a network of stratospheric balloons to provide Internet access in remote areas Simonite a. The altitude control is performed by adding or removing air inside the balloon, with the use of a fan. With this, it is possible to select altitudes where the wind is in a convenient direction.
The flight altitude is about 20 km, lasting up to days, using energy from solar panels. The idea is to launch a constellation of several balloons, forming a ring at determinate latitude Metz Several tests have been conducted with the release of dozens of balloons, in places like New Zealand, Australia and northeastern Brazil.
In February , following an agreement with the government of Sri Lanka, Google started tests to provide Internet access services in the country using the Project Loon balloons, in a joint work with local operating companies Tung Another important event in , in Puerto Rico, was the test of an autolauncher crane specially built for the project, enabling the launch of a balloon in just 30 minutes Google The Solara 50 was announced by Titan Aerospace in Warwick The aircraft has a wingspan of 50 m and a total weight of kg, with 32 kg payload.
It is expected that the Solara 50 will be capable of flying at 20 km for up to 5 years Aerospace Technology In May , the prototype of the Solara 50 was destroyed in an accident on its first flight, shortly after takeoff, in a test area in New Mexico, US. The accident was caused by structural failure of the wing due to air currents thermals at low altitude NTSB Google announced that it will continue the development of the Solara 50 Warwick In March , Facebook announced the purchase of the British company Ascenta with staff which participaded in he development of Zephyr at QinetiQ, in a deal valued at 20 million dollars Arthur and Michel The aircraft has four propellers driven by electric motors, with power supplied by solar cells during the day and rechargeable batteries at night.
The Aquila will fly between 18 and 27 km altitude, for a period of 3 months. It will be taken to the stratosphere by a helium balloon. It is expected the use of a laser connection to form a high-speed communications network. In case of obstruction by clouds, it will be used a radio connection with some reduction in data rate. According to Facebook, this service would connect millions of Indian citizens currently without access to the Internet.
In addition to these main HAP projects presented above, several others may be cited. In the United States, there are three projects in progress of medium- and high-altitude UAV, with the goal of 1 week or more autonomy, using hydrogen as a fuel: Two maneuverable balloon projects were supported by the DoD and NASA in the period from to ; however, they are currently paralyzed: These stratospheric balloons have controlability provided by a propulsion system installed in the suspended payload gondola. At the end of the mission duration, the payload in the form of an airplane is separated from the balloon envelope, which is discarded, and returns to the ground in a controlled flight DoD In Europe, several projects related to HAP were conducted with support of the European Comission, particularly in the period from to The main focus of these projects was research in telecommunications topics.
In the HeliNet Project, completed in , the Politecnico di Torino prepared studies for a stratospheric UAV denominated HeliPlat with a wingspan of 73 m, total mass of kg and payload of kg Romeo et al. The Advanced Research in Telecommunications Systems ARTES Project, from the European Space Agency ESA , completed in , made an estimate that the development of 2 stratospheric platforms with solar electric propulsion airplane and airship would require total resources of million euros about million dollars , over a year period ESA There are private companies with proposals for HAP airships projects, but without confirmation of financial resources allocation for the development of these initiatives, such as: The bibliometric analysis of scientific publications is an important tool to support forecasting of new technologies Daim et al.
In the present paper, these tools have been used to identify countries wich had more papers in the area of HAP and the temporal evolution of the scientific work, with the construction of logistic curves. The following databases were analyzed for searching scientific articles: Scopus, Web of Science and Google Scholar.
Scopus was selected because it has generated the largest number of results. The following search criteria query string were adopted, applied in any of the fields: In order to eliminate repetition and results without relation with the subject of this study, an analysis of each article abstract was performed.
Publications were considered valid when they were directly related to the HAP subject. In addition to the papers in the field of aeronautics, articles on energy conversion, remote sensing, and telecommunications were also included. As an example of topics that meet the search criteria but are irrelevant in this paper, studies related to atmospheric sciences, microsatellites and conventional high-altitude UAV HALE , as the Global Hawk, can be cited.
Although this filtering procedure is prone to error, it is considered that the influence of these errors on the final quantitative results is small. After filtering, 1, scientific papers directly related HAP were identified in the period from January to December The average from to was about 1 publication per year, with a total of 22 publications, and, therefore, this period was not included in the survey.
The total number of publications for each of the 5 countries with the largest number of papers was: Figure 16 shows, in a stacked chart, the distribution of scientific publications per year, for each of these 5 countries. From , China becomes the country that publishes the largest number of scientific articles on HAP, while, in other countries, there was a decline in publications. In this survey of scientific articles, China publications previous to were not identified. From these logistics curves, it may be estimated that the saturation limit in China should be of publications and, in other countries, of These estimations are valid provided that there are no significant changes in the current world scenario of HAPs, as a further increase in scientific interest in the subject due to expressive successful results of Google, Facebook, Airbus and Thales companies.
Based on an analysis of abstracts, a classification of the papers was conducted in the following topics: Table 1 presents the results of this classification for the total 1, articles and is also divided into China and other countries.
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Most of the articles related to balloons are on the StratoSail concept that a wing is suspended by a long cable attached to a stratospheric balloon, allowing a limited navigation capability for the balloon Nock et al. Although a significant number of papers published in China on airships might indicate the existence of a centralized governmental orientation for the future development of a stratospheric airship, it was not found any reference to confirm this hypothesis. Some of the Chinese articles mention possible military applications for high-altitude airships, for example, as a platform for GPS signal jamming for defense against cruise missiles Li et al.
Designing aircraft to operate in the stratosphere as HAP imposes major technological challenges, with the main ones being: Some aspects of each of these challenges will be discussed next. As the lift, both aerodynamic and aerostatic, which counteracts the weight of the aircraft, is directly proportional to the air density, the wing area in the case of airplanes and the volume in the case of airships and balloons, designed to operate as HAP, have to be about 14 times larger than if the aircraft were dimensioned to sea-level conditions, considering the same design features, such as total weight, aerodynamic shape and operation speed.
These large dimensions lead to very severe optimization requirements of HAPs structural weight. In the case of airships and balloons, the envelope material must have low weight characteristics, high strength, high ability to withstand damage tear, pin holes , low permeability to lifting gas, maintain flexibility at low temperature and low degradation with UV radiation and ozone Zhai and Euler It is typically used laminated with an outer layer, for environmental protection and retention of gas, and internal fibers, for structural strength, joined by an adhesive layer.
A typical HAP laminate has thickness of 0. Also for HAPs of the airplane category, lightweight structures are essential.
The weight of various components of a HAP airplane is distributed along the wingspan to reduce the structural stress on the wing. As an example, on the Zephyr, the batteries are installed in the wing spar Rapinett One of the technologies required for the design of these large and very flexible wings is analysis of aeroelastic phenomena, such as flutter, and its influence on the stability and control of the airplane.
These optimized structures for high-altitude flights have the disadvantage of fragility at gust conditions found at lower altitudes. Examples of this weakness are the accidents of Helios in and Solara 50 in Like any aircraft, HAPs require a source of energy for the propulsion system and the electricity supply to their systems and payload.
HAP projects with the objective of achieving very long endurance, on the order of months and even years, prevent the use of energy sources based on traditional aviation fuel, as avgas aviation gasoline or jet fuel aviation kerosene , and other less common fuels, such as diesel or hydrogen. Nuclear power is a technically feasible solution, but politically not acceptable by society, because of the associated risks Sweetman The potential for power transmition to the aircraft from ground stations, via microwave or laser, has been studied, but it is still far from being operationally viable Dickinson The most commonly adopted solution for very long endurance HAP is, during the day, the solar energy converted into electricity by means of photovoltaic cells solar cells , and part of this electricity is used to charge a storage system, usually rechargeable batteries or RFC for later use at night Nickol and Guynn The lighter-than-air LTA aircraft are directly influenced by the temperature difference between the lifting gas and the external atmosphere.
This effect is called superheating, when the temperature of the internal gas is higher than that of external air, or supercooling, in the opposite case Harada et al. The influence can be in aerostatic lifting force or internal pressure, in the case of superpressure airships.
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The thermal management of HAP airships, including the mathematical modeling of the thermal balance and the use of insulating materials, is a technology that needs to be intensified Wu et al. The HAP projects, both airplanes and airships, are optimized for the stratosphere conditions, at altitudes close to 20 km, where the thin air is relatively calm and the wind speed is low Jamison et al.
As result, HAPs have low power propulsion systems and light and fragile structures, when compared to aircraft designed to operate at lower altitudes. The strong winds and turbulence found in the troposphere can lead to loss of the HAP, such as the accidents of Helios in and Solara 50 in Therefore, an important point in the HAPs operation at low altitude, especially in phases of launch and recovery, is the choice of weather windows where the weather conditions are appropriate Brooke An example of these limitations is that, for the operation of Zephyr, it is chosen calm weather conditions, such as those found in desert regions Rapinett The domain of technologies for weather forecasting in the operations area and for simulation of the aircraft trajectory at the conditions found at low altitude is essential to the successful operation of HAPs.
Another important aspect to be considered in HAP operations is the coordination with the airspace control organizations. Most of the time of flight of a HAP is above the air control altitude limit, usually defined at 20 km 65, ft. The launch and recovery phases, which occur at lower altitudes, should be planned in conjunction with the airspace control agency, with the definition of specific segregated areas for that operation.
Aspects in the field of international law related to the overflight of other countries also need to be analyzed. HAP operation by long flight periods, for months or even years, will require equipments with a high level of reliability Bolkcom Another important point is that the low pressure at high altitudes can cause arcing problems in electrical components Ferguson and Hillard For an operational HAP, it is likely that space equipments and components are adopted, usually of very high cost.
The high-reliability issues must be applied even to the HAP system as a whole, including ground stations and data link.
Based on the evolution of HAP projects and the current state-of-the-art of its technologies, it is possible to perform an analysis of technology trends in this area. Most of the current projects are of UAVs, due to the goal of achieving very-long-duration flights. This trend should be increasingly strengthened. For these long flights, it is expected to increase the use of solar cell panels photovoltaic cells as the primary energy source of HAPs. For nighttime, it is unclear whether there will be a preference for advanced rechargeable batteries, such as lithium-sulfur, or RFC. These two technologies are expected to have significant advances in the coming years due to the evolution of electric car industry.
This predominance of airplane projects does not seem to be a confirmed trend for medium and long term. The number of technical publications in China on HAP airships may be an indication that airships will still be a significant segment of future HAP projects.
High-Altitude Platforms — Present Situation and Technology Trends
Analyzing the information on the 12 major HAP projects, presented in this paper, it is noticed that 7 were closed without achieving results that would ensure continuity and 5 are in progress Airbus Zephyr, Thales Stratobus, Google Loon, Google Solara 50 and Facebook Aquila. This finding indicates that the technological maturity Technology Readiness Level — TRL for the development of HAP aircraft has not reached a level sufficiently high to ensure their certification, serial production and commercial operation. Customer reviews There are no customer reviews yet. Share your thoughts with other customers.
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