This work aims to assess the necessary power for a tethered high-altitude unmanned airborne platform, in which the propulsion system and payload are powered from a groundbased cable power source. A summary and solution to a system of differential equations are given to describe the spatial position of the cable and its action on the high-altitude unmanned platform in gust conditions. The mass of the airborne platform including payload, the effect of the cable on the airborne platform, and its wind resistance are taken into account when calculating the power. The paper describes the system architecture, consisting of a ground station, a cable, and an airborne platform, and presents the results of field tests, which showed good agreement with the results of theoretical studies.