Unmanned stratospheric flight offers opportunities nearly as broad as space flight. Since the late 1950s, high-altitude station keeping platforms have been under research. But materials have improved since these early days and key systems can now be made simpler, lighter and more reliable. In summer 2001 an unmanned solar powered U.S. platform reached an altitude of 29 km and clearly showed: The time has come for entering the market of stratospheric platforms.
The main objective of this study is to explore the grounds for the development and operation of a European stratospheric platform based on a sound analysis of possible service areas - mainly in the area of telecommunications, assessment of available and future technologies, to perform a conceptual design for the best suited platform concept answering the needs of future telecommunication markets.
The figure above shows two design alternatives for stratosheric platforms: unmanned stratospheric airship or aeroplane.
Stratospheric platforms can be considered as a new telecommunications infrastructure element which will close the gap between terrestrial and space borne telecommunication elements.
This would be an innovative way of overcoming the shortcomings of both the terrestrial tower-based and satellite systems to provide mobile communications via stratospheric platforms or so called High Altitude Platform Stations (HAPS). Single HAPS with communications payloads (bent pipe transponders and phased array antenna) onboard can replace a large number of terrestrial base stations and their backhaul infrastructure (microwave or optical links). Furthermore, high altitude platform stations provide a faster convergence route between communications and broadcasting services. High altitude platform stations have already been accepted by International Telecommunication Union (ITU) as an alternative method of delivering the IMT-2000/UMTS (International Mobile Telecommunications System 2000/Universal Mobile Telecommunications System) services.
With stratospheric platforms and the corresponding stratospheric services new business opportunities will appear to provide new and cost efficient telecommunication services for the world of tomorrow.
In Japan and the United States research and commercial initiatives have been started in this field. Now in Europe, research agencies as well as industry are becoming more active in this global competition.
Because mobile communication is the preferable candidate for stratospheric services, a next generation mobile communication system architecture is going to be defined, incorporating terrestrial, satellite based and stratospheric platform-based infrastructure with a full integration between 3G, DVB, DAB and satellite to gain a maximum increase in performance.
For the system architecture, all relevant elements such as ground segment (up-/downlink, network control centre, resource control centre) and flight segment (High Altitude Platform Station (HAPS), communication payloads, antenna) are specified and designed in a conceptual way. A major part of such a system is the platform antenna. Here a new approach for large sized, high gain and re-configurable antennas is needed either incorporating the control mechanisms on the platform or on the ground. This functionality split has to be investigated as well as some concepts for the radiating antenna elements themselves.
The figure above shows a possible integrated communications system architecture based on satellites, terrestrial infrastructure and stratospheric platforms.
Starting from an analysis of services that will mostly benefit from the availability of quasi-geostationary platforms, at least 3 of the most promising services from the stratospheric platform point of view will be selected. For these services a detailed financial assessment will be performed on realistic market data and trends to show their economic potential clearly.
Parallel existing stratospheric platform concepts will be reviewed and the most suitable will be selected for a further detailed design on system and subsystem level. A subsequent proof-of-concept will identify the main critical technologies and design aspects. Technological solutions will be proposed and summarized in an overall platform system concept. The financial assessment of market opportunities and cost estimation for platform development will result in an overall business case.
The results of the study will be presented to the Agency with a first draft road map of a European stratospheric platform initiative. It will outline how such a programme can support the launch of new commercial products and services as well as how space activities can gain from stratospheric platform activities.
The project was started in 2002/09 and finished in 2005/09. The main results are as follows:
- Stratospheric Service Candidates
Stratospheric platforms have to position themselves well with existing terrestrial and satellite based infrastructures. Regards to co-existing networks such as mobile network, broadcast network, and fixed network the most promising stratospheric service candidates according to technical feasibility and market potential are broadband connectivity, 3G base-station service and DAB/DVB-T broadcasting.
- Stratospheric Platform Designs
Two reference configurations for stratospheric platforms, an aerostatic and an aerodynamic configuration, both electrical driven and solar powered were investigated in detail. Most of critical technologies are common to both platform categories. Therefore, a stepwise development approach using both types of platforms in the prototype and test phase was outlined. The development effort for a pair of European stratospheric platforms, esa-DYN (aerodynamic) and esa-STAT (aerostatic) platforms is estimated in total to around 270 MEUR over 10 years. This includes technology research, sub-scaled demonstrators and prototypes. Rough cost estimation was performed based on analogue experience for manned airships and manned airplanes which show a linear relation between platform life cycle costs and maximum take off mass.
A total life cycle cost model shows that even at market sizes well above the size, which can be expected at market entry, the investigated stratospheric services cannot compete with terrestrial based services under European economic conditions. The most promising candidate is 3G base-station service which is approx. 30% higher in total life cycle cost than existing terrestrial 3G networks. Taking into account the introduction of terrestrial based telecommunication services in some of the promising non-European countries may be prevented by non-technical, non-economic reasons; 3G could be the entry point for stratospheric tele-communication services.
- European Approach
In Europe the interests in stratospheric platforms are continuously growing. Currently there is no European coordination in this field. Here a holistic approach in needed to keep Europe active in this strategic important area of High Altitude Very Long Endurance unmanned aerial vehicles. A joint activity of ESA with its well known background in stratospheric key technologies and the European Commission Research Directorate is recommended for future continuous research on stratospheric platforms focussing on pilot applications in telecommunications and GMES.