Analysis of suitable weather conditions for the operation of HAPS (High Altitude Pseudo Satellites)

Remote-controlled airplanes are increasingly being used for special purposes. For example, the use of stratospheric platforms for telecommunications purposes is planned. These so-called HAPS (High Altitude Pseudo Satellites) are lightweight aircraft-like vehicles with very large wingspans. They fly very slowly, are powered by hydrogen and can remain in the stratosphere for several days to several weeks. The OBeLiSk project, an R&D project funded by  the Federal Aeronautical Research Programme (LuFo VI-1), is currently developing an operational concept for safe and efficient airspace integration of such stratospheric platforms. Due to the structural limitations imposed by the lightweight design, HAPS can reach their limits very quickly in certain weather conditions. This applies in particular to operations at the airport during take-offs and landings. The limit values above which weather-related limitations can lead to massive impairments or even structural fractures of the HAPS are specified by the HAPS designers.

In the analysis presented here, one of the specifications was that certain wind speeds must not be exceeded during take-offs and landings and that no precipitation must occur. The specified limits can be used to define "potential operating hours", i.e. hours during which the weather situation at an airport allows HAPS to take off or land safely. Based on hourly measured values of a long-term period, frequencies of potential operating hours at airports geographically distributed over Germany were analysed. As expected, a minimum of potential operating hours in the winter months and a maximum in the summer months were observed when considering multi-year mean annual cycles. For the planned operational concept, the multi-year mean diurnal variations were of particular interest in order to find out which times of day are suitable for HAPS take-offs and landings. The results here were largely independent of the geographical location of the airports in Germany.  There was a maximum of potential operating hours at night in spring, summer and fall and in the late afternoon in the winter months.

The fact that wind plays a significant role in weather-related restrictions was to be expected. However, an additional sensitivity analysis showed specifically how many additional potential hours of operation could be achieved if the maximum limit at which HAPS could still be operated safely were increased by, say, one node. In this way, specific recommendations can be made to HAPS designers. In addition, the analyses can identify airports that are particularly well suited for conducting HAPS take-offs and landings.