Aerospace Engineering Area University of León/Spain

HAPPIEST is a study funded by the European Space Agency and led by the Aerospace Aera of University of León. Other collaborators are Thales Alenia Space España, Aerobotics Germany and Deimos Engenharia Portugal.

The development of High Altitude Pseudo-Satellites (HAPS) has reached an outstanding level of maturity, with several flight demonstrations that augur soon to have operational capabilities. ESA, aware of the synergies among satellite and HAPS services, setup the HAPPIEST study to analyse the impact of the irruption of aerostatic HAPS into the telecommunications market, currently covered by space and terrestrial networks. Furthermore, some complementary payloads can serve interesting applications such as Earth observation and navigation services. The objective of HAPPIEST is to study the role of Aerostatic HAPS in the future Telecommunication Networks, identifying the most promising services and the resulting hybrid networks. In particular, a conceptual design has been developed in two reference scenarios where HAPS services are more valuable from the commercial point of view. This effort enables technical discussion on the technology maturity, economic estimations and programmatic solutions for a future ESA HAPS programme. The setup of a development roadmap for HAPS is another objective of the study.

Communication services

There are many communication services than can be offered by integrating HAPS into existing terrestrial or space networks. HAPS provide fast deployment capability, payload upgradability, simpler and/or smaller terminals and higher capacity links. Their geographical coverage is in between terrestrial and space based systems. After a comprehensive analysis of capabilities, the interesting services are: Direct To Home (DTH) Broadband, trunking, backhauling, High Throughput Services, tactical communications, mobile broadband and 5G. The provision of these services must be implemented in the bands allocated to HAPS by the current ITU regulation.

High altitude pseudo-satellites (HAPS) can offer many telecommunication services at regional scale. The most promising ones from the point of view of the economic and technical feasibility are:

- Tactical communications: back-up, temporal or precursor system to provide telecommunication services when natural disasters occur (e.g. earthquakes or floods) or when the scenario lacks from the required infrastructure (e.g. remote areas or deep sea) or when augmented performance is required (e.g. 5G). Digital radio and broadband services are among the proposed tactical communication services. HAPS can also be used as concept proof for new satellite services.

- Backhauling: the most valuable backhauling service among the ones studied is the use of HAPS as part of the EDRS Space Data Highway. The downlink from a satellite can be carried out in two steps: from the satellite to the HAPS and from the HAPS to ground. The first hop is prone to the use of optical links as it is free from atmospheric effects. The short path of the second, when compared to satellite height, improves the link budget enabling smaller antennae (cost saving) or wider bandwidth (revenue increase).

Worldwide frequencies allocated to HAPS are around 5 GHz (limited bandwidth available) and 47/48 GHz (high degradation and availability issues). Although feasible links have been demonstrated, the recommendation is to get frequency slots in Ku/Ka bands in order to provide better access to services.

Complementary services

HAPS provide unprecedented persistent remote sensing with very high resolution. Besides, their long endurance enables the provision of long-term services similar to satellites. Although with limited coverage, HAPS also offer certain mobility and payload interchangeability. Thus, HAPS can complement and multiply the capabilities of current airborne and space based sensors. A trade-off analysis shows wide market niches in sectors such as security, maritime, emergency management, local planners and agriculture, with both private users and governmental bodies behind this interest. Besides, the availability of a HAPS platform opens opportunities for the provision of navigation services, either with stand-alone assets or with additional infrastructure to complement/augment existing infrastructure. GNSS signals also enable studies of water levels, biomass and atmosphere.

The services selected for further study present best operator or customer profits, wide demand, interoperability with currently existing systems and technical feasibility. As a conclusion of a quantitative review of the Earth observation services, the ones showing larger gaps subject to be covered by HAPS are those related to security and defence, maritime applications, local planning, emergencies and agriculture. GNSS-based services can help with sea level monitoring and biomass estimations (signal reflectometry) as well as atmospheric research or meteorology (radio occultation).

 

In general, the HAPS payloads are evolutions from terrestrial, airborne or spaceborne operational instruments, including customised environmental protections and adaptations to required mission endurance. Besides, concept proof experiments can be developed from stratospheric balloon campaigns.

Despite their undoubtable value for commercial use, the stratospheric aerostatic platforms exhibit more immature technology levels. Although key technology is available in most of the subsystems (TRL4/5), there is no current evidence of operational capabilities of these systems as high as 20-km from sea level (TRL6). After a comprehensive analysis of representative environments for tests, a detailed development roadmap is proposed:

Following a staggered approach, models can be tested every 2 years, increasing from 15 to 20 km altitude, 25 to 250 kg payload mass and endurances from few days to a full year. This approach minimises the technical risk whereas enables a progressive development of the physical and regulatory infrastructures. First model can be flying in 2020 to have a full-featured product in 2025.

 

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