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. In the 1990 and 2000 decades, several projects were launched, but very few had continued. 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. This article aims to survey the history of HAPs, the current state-of-the-art (April 2016), technology trends and challenges. 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.

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This work presents the effect of NiO on the thermal behavior and the crystallization kinetics of glasses lying near the stoichiometric cordierite composition nucleated with TiO2. Three glasses with NiO content varying between 1 and 5 mol% have been synthesized in Pt crucibles. Activation energies for structural relaxation and viscous flow have been calculated using the data obtained from differential thermal analysis (DTA). Kinetic fragility of the glasses along with other thermal parameters has been calculated. Non-isothermal crystallization kinetic studies have been employed to study the mechanism of crystallization in all three glasses. The crystallization sequence in the glasses has been followed by x-ray diffraction analysis of the heat treated glass samples in the temperature range of 800–1200 °C. μ-cordierite has been observed to be the first crystalline phase in all the glass samples after heat treatment at 850 °C, while NiO plays an important role in determining the crystallization sequence at higher temperatures, leading to the formation of α-cordierite.

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