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High Altitude Aeronautical Platforms


Published on Dec 06, 2015

Abstract

Affordable bandwidth will be as essential to the Information Revolution in the21 st century as inexpensive power was to the Industrial Revolution in the 18 th and 19 th centuries.

Today's global communications infrastructures of landlines, cellular towers, and satellites are inadequately equipped to support the increasing worldwide demand for faster, better, and less expensive service. At a time when conventional ground and satellite systems are facing increasing obstacles and spiraling costs, a low cost solution is being advocated.

This paper focuses on airborne platforms- airships, planes, helicopters or some hybrid solutions which could operate at stratospheric altitudes for significant periods of time, be low cost and be capable of carrying sizable multipurpose communications payloads. This report briefly presents an overview about the internal architecture of a High Altitude Aeronautical Platform and the various HAAPS projects.

High Altitude Aeronautical Platform Stations (HAAPS) is the name of a technology for providing wireless narrowband and broadband telecommunication services as well as broadcasting services with either airships or aircrafts. The HAAPS are operating at altitudes between 3 to 22 km. A HAPS shall be able to cover a service area of up to 1'000 km diameter, depending on the minimum elevation angle accepted from the user's location.

The platforms may be airplanes or airships (essentially balloons) and may be manned or un-manned with autonomous operation coupled with remote control from the ground. While the term HAP may not have a rigid definition, we take it to mean a solar-powered and unmanned airplane or airship, capable of long endurance on-station -possibly several years.

Various types of platform options exist: SkyStation™, the Japanese Stratospheric Platform Project, the European Space Agency (ESA) and others suggest the use of airships/blimps/dirigibles. These will be stationed at 21km and are expected to remain aloft for about 5 years. Angel Technologies (HALO™), AeroVironment/ NASA (Helios) and the European Union (Heliplat) propose the use of high altitude long endurance aircraft. The aircraft are either engine or solar powered and are stationed at 16km (HALO) or 21km (Helios). Helios is expected to stay aloft for a minimum of 6 months whereas HALO will have 3 aircraft flying in 8- hour shifts. Platforms Wireless International is implementing a tethered aerostat situated at ~6km.

A high altitude telecommunication system comprises an airborne platform - typically at high atmospheric or stratospheric altitudes - with a telecommunications payload, and associated ground station telecommunications equipment. The combination of altitude, payload capability, and power supply capability makes it ideal to serve new and metropolitan areas with advanced telecommunications services such as broadband access and regional broadcasting. The opportunities for applications are virtually unlimited. The possibilities range from narrowband services such as paging and mobile voice to interactive broadband services such as multimedia and video conferencing.

For future telecommunications operators such a platform could provide blanket coverage from day one with the added advantage of not being limited to a single service. Where little or unreliable infrastructure exists, traffic could be switched through air via the HAPS platform. Technically, the concept offers a solution to the propagation and rollout problems of terrestrial infrastructure and capacity and cost problems of satellite networks.

High Altitude Aeronautical Platform Stations (HAAPS)

High Altitude Aeronautical Platform Stations (HAAPS) is the name of a technology for providing wireless narrowband and broadband telecommunication services as well as broadcasting services with either airships or aircrafts. The HAAPS are operating at altitudes between 3 to 22 km. A HAAPS shall be able to cover a service area of up to 1'000 km diameter, depending on the minimum elevation angle accepted from the user's location. The platforms may be airplanes or airships (essentially balloons) and may be manned or un-manned with autonomous operation coupled with remote control from the ground.

Various types of platform options exist: SkyStation™, the Japanese Stratospheric Platform Project, the European Space Agency (ESA) and others suggest the use of airships/blimps/dirigibles. These will be stationed at 21km and are expected to remain aloft for about 5 years. Angel Technologies (HALO™), AeroVironment/ NASA (Helios) and the European Union (Heliplat) propose the use of high altitude long endurance aircraft.

The aircraft are either engine or solar powered and are stationed at 16km (HALO) or 21km (Helios). Helios is expected to stay aloft for a minimum of 6 months whereas HALO will have 3 aircraft flying in 8- hour shifts. Platforms Wireless International is implementing a tethered aerostat situated at ~6km.

A high altitude telecommunication system comprises an airborne platform – typically at high atmospheric or stratospheric altitudes – with a telecommunications payload, and associated ground station telecommunications equipment. The combination of altitude, payload capability, and power supply capability makes it ideal to serve new and metropolitan areas with advanced telecommunications services such as broadband access and regional broadcasting. The opportunities for applications are virtually unlimited.

The possibilities range from narrowband services such as paging and mobile voice to interactive broadband services such as multimedia and video conferencing. For future telecommunications operators such a platform could provide blanket coverage from day one with the added advantage of not being limited to a single service. Where little or unreliable infrastructure exists, traffic could be switched through air via the HAAPS platform. Technically, the concept offers a solution to the propagation and rollout problems of terrestrial infrastructure and capacity and cost problems of satellite networks. Recent developments in digital array antenna technology make it possible to construct 100+ cells from one platform.

Linking and switching of traffic between multiple high altitude platforms, satellite networks and terrestrial gateways are also possible. Economically it provides the opportunity for developing countries to have satellite-like infrastructure without the funds flowing out of the country due to gateways and control stations loc ated outside of these countries.

Power System & Mission Requirements

Various power system components and mission requirements affect the sizing of a solar powered long endurance aircraft. The aircraft power system consists of photovoltaic cells and a regenerative fuel cell. for the power system, the greatest benefit can be gained by increasing the fuel cell specific energy.

Mission requirements also substantially affect the aircraft size. By limiting the time of year the aircraft is required to fly at high northern or southern latitudes a significant reduction in aircraft size or increase in payload capacity can be achieved.

Due to the high altitude at which these aircraft will be required to fly (20 km or higher) and the required endurance (from a few weeks to a year) the method of propulsion is the major design factor in the ability to construct the aircraft. One method of supplying power for this type of aircraft is to use solar photovoltaic (PV) cells coupled with a regenerative fuel cell. The main advantages to this method over others such as open cycle combustion engines or air breathing fuel cells is that it eliminates the need to carry fuel and to extract and compress air at altitude which can be a significant problem both in gathering the required volume of air and in rejecting the heat of compression.

In order for a solar powered aircraft to be capable of continuous flight, enough energy must be collected and stored during the day to both power the aircraft and to enable the aircraft to fly throughout the night. The propulsion system consists of an electric motor, gear box and propeller.

The aircraft with amorphous silicon cells performed better than the CLEFT GaAs powered aircraft at lower aspect ratios and both amorphous silicon and CLEFT GaAs performed significantly better then the GaAs/Ge and silicon powered aircraft. As the efficiency increases, the corresponding reduction in aircraft size decreases. Fuel cell performance has a significant impact on size and performance of a solar powered aircraft. There are modest size reductions with increasing fuel cell efficiency; however, the size reductions which are gained by an increase in the specific energy of the fuel cell are substantial.

Aircraft size increases significantly with increasing altitude. The specified time of year (date) and latitude determines the charge/discharge period for the energy storage system as well as the amount of total solar energy available. The winter solstice, December 22, is the date with the longest discharge period and smallest amount of available solar energy. This date was chosen as the baseline because it is the time of lowest daily average solar flux in the northern hemisphere and therefore represents a worst case situation. Any aircraft power system and mission configuration which is feasible at this date would be capable of operating throughout the year. However, by varying the required latitude throughout the year, aircraft size can be reduced.

Payload and payload power required also has an effect on the aircraft size. Mission requirements will mostly determine the amount and type of payload. In most situations lightweight, low powerinstruments, similar to satellite equipment, will need to be used.

If very light weight amorphous silicon arrays or any thin film array of similar performance can be mass produced, they would have significant advantages over individual-celled rigid arrays. The main advantage would be their incorporation onto the wings of the aircraft. Since they are flexible and can be made in large sheets they can conform to the shape of the wing. This allows for fairly easy installation directly over the wing surface. Also there would be no need to wire each individual cell together as is necessary with individual rigid cells. In order to make the commercial construction and maintenance of this type of aircraft practical ,light weight, flexible PV arrays will need to be used














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