The need for a worldwide broadband communication infrastructure is great, today and more so in the future. Mobile 5G communication and the Internet of Things (IoT) require a high-performance communication infrastructure in terms of high data rates, low latency, reliability, and ubiquitous availability. Electromagnetic waves carry the communication either through copper wires, fiber-optic guides or by radio waves. Wires and cables are in or on the ground, radio waves use towers, satellites or airborne platforms to link users.
Technical and commercial issues co-determine the preferred type of infrastructure. Populated areas in developed countries feature the cable and radio tower system, which requires high investments and thus needs many customers to support the system. Terrestrial systems can provide high data rates with low latency; however, availability is a problem in many areas of our world.
Communication satellites have been in use for many years, particularly in geostationary orbit (GEO) at 36,000 km altitude and low earth orbit (LEO) between 350 km and 2,000 km altitude. A radio signal’s travel time to and from a GEO satellite is a few hundred milliseconds and causes an unacceptable latency for many applications. LEO satellites can deliver high bandwidth at low latency. This requires tens of thousands of satellites and a large number of dedicated terminals or base stations with radio masts for mobile networks. Low-orbit satellites suffer from small atmospheric drag resulting in a limited lifetime and ultimate re-entry into the atmosphere. Permanent replacements of single spacecraft and a complex technical infrastructure to operate the system are cost drivers.
HAPS, high-altitude platforms, operate at around 20 km altitude and occupy a position between earth orbit and ground. They are less complex than satellite systems and can be considered as elevated radio towers as trials with balloons and airplanes have proven. Static or aerodynamic lift can be used for HAPS, i.e., balloons or airships and airplanes. Static lift vehicles are more difficult to handle and to control than airplanes on which we will focus here.
The introduction of HAPS as platform for world wide communication services requires the application of some only recently resolved technical challenges: Payload capacity, energy supply, light weight airplane structures and unmanned operations in civil airspace. Existing solar powered HAPS require ultralight aircraft whose year-round operation is limited to the tropics near the equator. The power efficiency of solar cells is fairly limited and only a limited power of about 100-1000 W is available for the payload. This limits the capacity of the telecommunication performance.
The articles on this website shall illustrate HAPS concepts and their need for the global information and communication infrastructure.