The term “High Altitude Long Endurance” (HALE), which has sometimes been used to label HAP, is generally more associated with conventional unmanned aerial vehicles (UAVs), with service ceiling of about 18 km, as the Global Hawk. Over the years, several terms have been used for this type of aircraft, such as: “High Altitude Powered Platform”, “High Altitude Aeronautical Platform”, “High Altitude Airship”, “Stratospheric Platform”, “Stratospheric Airship” and “Atmospheric Satellite”. This fact shows that, at the time, there was a growing interest in HAP utilization as a complement to terrestrial and satellite-based communications network. At this conference, the term “High Altitude Platform Station” (HAPS) has been established, defined as a telecommunications station located at an altitude of 20 to 50 km and at a specified fixed point relative to the Earth. Immediately after the tropopause, which has a constant temperature of about −60 ☌, the stratosphere starts at an altitude of 7 km at the poles and 18 km at the Equator, extending to around 50 km ( Widiawan and Tafazolli 2006).Ī remarkable fact for the HAPs concept was the initial definition of a frequency band for its telecommunications services on the World Radiocommunication Conference 1997 (WRC-97), organized by the International Telecommunication Union (ITU), which deals with the regulation of the use of radio frequencies. The stratosphere is the layer of the atmosphere where the temperature starts to increase with altitude. These aircraft may be airplanes, airships or balloons, manned or unmanned. High-altitude platforms (HAPs) are aircraft positioned above 20 km altitude, in the stratosphere, in order to compose a telecommunications network or perform remote sensing, for civilian or military applications. Large projects were started in the United States, Japan and South Korea ( Levine 2004 Eguchi and Yokomaku 2000 Lee et al. In the 19 decades, several projects were launched in order to explore the potential application of high altitude platforms for telecommunications and remote sensing. KEYWORDS: High-altitude platform, High-altitude airship, Stratospheric satellite, Unmanned aerial vehicle, Technological challenges, Technology trends. The main focus of this review will be on technologies directly related to the aerial platform, inserted in the aeronautical engineering field of knowledge, not detailing aspects of the telecommunications area. This article aims to survey the history of HAPs, the current state-of-the-art (April 2016), technology trends and challenges. In 2014, 2 major Internet companies (Google and Facebook) announced investments in new HAP projects to provide Internet access in regions without communication infrastructure (terrestrial or satellite), bringing back attention to the development of HAP. In the 19 decades, several projects were launched, but very few had continued.
High-altitude platforms (HAPs) are aircraft, usually unmanned airships or airplanes positioned above 20 km, in the stratosphere, in order to compose a telecommunications network or perform remote sensing.
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