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Stratobus: Autonomous surveillance and telecoms 20km above Earth

Stratobus

Yannick Combet, Programme Manager of the StratobusTM project, describes the technologies, missions and capabilities of the High Altitude Platform System under development by Thales Alenia Space France.

Project Stratobus, developed by Thales Alenia Space France, is an autonomous stratospheric system, High Altitude Platform System (HAPS) which includes the vehicle itself, its payload and the ground infrastructure.

It is powered by solar energy and can withstand its steady-state position in the stratosphere for up to one year, autonomously, providing a geostationary platform for multi-mission purposes.

Stratobus is a 140m long, 32m diameter airship positioned at an altitude 18-20km in the lower layer of the stratosphere, where the winds are moderate and air density is still sufficient to allow buoyancy. The Stratobus platform consists of a flexible envelope maintained in shape by helium in overpressure. Its total weight is around 9,000kg including a payload of over 250kg. These characteristics mean that it can reach altitudes around 20km and thus enjoy a visibility horizon of 500km.

The platform and its on-board solar energy allow it to counter winds of the order of 25 m/s and thus remain stationary over a point or area of interest with high availability. It is the only platform offering the ability to perform long-duration missions. It needs to come down to Earth only once a year for maintenance and to top up its helium.

Why stratospheric?

An operating altitude of 20km is a good compromise between taking advantage of the relatively weak winds and offering enough air density to ensure buoyancy. In addition, at this altitude the airship is still relatively close to the Earth: above air traffic, but at a height that provides very-high-resolution regional coverage.

Stratobus missions

Stationed at the edge of the stratosphere, about 20km above sea level, just above air traffic, but much closer to the Earth than a satellite, Stratobus is able to provide regional coverage at a very high level, high resolution. The airship can perform many missions, from precision surveillance of a given area or control of our environment, to telecommunications and navigation operations. It is intended for many applications such as surveillance of borders, oil operations and maritime piracy, vessel identification, air quality measurement, GSM network reinforcement during exceptional events and improved GPS systems in heavy traffic areas. As part of commercial telecommunications missions, Stratobus complements the global telecommunications ecosystem by offering fixed and mobile connectivity solutions in addition to those provided by terrestrial or satellite networks.

Operational costs are low and its ecological footprint based on a hydrocarbon-free concept, is minimal.

Stratobus key technologies

Previous attempts at developing a permanent stratospheric high-capacity airship have faced technological or operations issues.

The Stratobus airship incorporates many technological innovations. The keys are mass and energy managements. Its 1000 m² solar generator and its high-energy density batteries are able to provide a large energy reserve for the airship, day or night, maximising solar energy while minimising the mass and surface area of the envelope.

In order to capture a maximum of solar flux, the balloon rotates around its main axis allowing it to position its solar generator facing the sun at any time of the day and in any season. Another key element is the design of the envelope itself. This has to take into account the structure of the airship and the sealing within a very low surface mass.

Stratobus timescales

A structuring co-engineering phase for the project started in 2016 at the Cannes site with Thales Alenia Space and its partners.

The development was split into two phases. The first phase was devoted to the preliminary study of the platform and technological demonstrations. The second phase related to the development of the system solution, including the platform, its ground segment and the missions.

During Phase 1, the analyses and preliminary design were correlated with numerous mock-ups. More than 3,500 physical tests have been carried out, from the basic component to the small-scale demonstrator to make sure that numerical models correlate to reality. All the technologies have been tested and for many in a representative environment. Phase 1 was closed in 2020 and the consortium concluded that the Stratobus concept was feasible with the technologies mastered.

Phase 2 was initiated in 2019 with, initially, a study phase of missions and operational concepts.

An operational demonstration stage is planned for 2024 to 2025 on the basis of small-scale models (60-meters long) called MVP for Minimum Viable Product. These demonstration phases are expected to take place on the Canary Islands. As soon as the stratospheric demonstration on a reduced scale is completed, the first full-scale operational model will be built and tested. The overall schedule depends on the financial scheme that is a permanent challenge for such a monumental development. In the meantime, Thales Alenia Space has started exclusive negotiations with the South of France region to define all the procedures regarding the facility that will produce the flight models.

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