To overcome the high costs of conventional satellites,
researchers are looking at solar-powered craft hovering at high
altitude to deliver cheaper telecoms.
With so many protests against mobile phone masts and warnings that
space is filling up with satellites and other junk, it would be
easy to believe there was nowhere left to put equipment to transmit
the radio signals we rely on for our communications
infrastructure.
However, a project being carried out by researchers at the
University of York, in concert with organisations across Europe,
aims to exploit a layer of the atmosphere currently unused. The
idea is simple enough. Rather than use a rocket to launch an
expensive satellite into space, why not float it at high altitude
in the Earth's atmosphere?
The £3.9m European Commission-funded Capanina project aims to
develop High Altitude Platforms (Haps) - solar-powered aircraft and
airships - which can be kept practically stationary at a height of
about 20km. Such aircraft can be launched and maintained at a
fraction of the cost and time it takes to lay cables underground or
launch conventional satellites.
The aircraft carry transponders for services such as mobile phones,
broadband internet, digital television and radio, and military and
civilian surveillance. They maintain their position using
solar-powered electric motors.
David Grace, of the University of York's communications research
group, said, "The main benefit is that high-capacity communications
can be achieved with less communications infrastructure and can be
quickly deployed."
One example of where the technology could be used is to assist in
disaster relief, or for emergencies. Haps could also be used to
provide a communications infrastructure where it currently does not
exist, especially over large areas in countries such as India or
Brazil, or in rural areas.
The project aims to deliver network bandwidth of 120mbps within a
Hap's coverage area, which has a 60km diameter. Vehicles travelling
at up to 300km per hour on the ground would be able to access the
communications infrastructure when travelling within the coverage
area.
The build and launch costs of Haps are favourable compared to
satellites. Whereas the cost of a satellite launch can run into
millions of pounds, Hap launch costs are minimal.
Grace said that excluding payloads, solar-powered aeroplane-type
Haps are likely to cost about £3.5m and airship-based Haps will
cost in the region of £17.6m. "Satellites typically cost upwards of
£88.4m," he said.
An aircraft Hap requires an airfield and a runway to launch, but an
airship Hap requires just a hangar or a ship.
In terms of ongoing maintenance, the Hap itself requires
maintenance only when it lands.
The on-station altitude for a Hap is between 17km and 20km, where
it needs a power source to maintain its position within a 6km
radius. The aircraft continually flies into the wind and uses
electric motors to avoid drifting and so maintains a static
position.
In the 17km to 20km altitude range, wind speeds average 120km an
hour, much slower than the jetstream, which blows at the height
airliners travel. Because of a temperature inversion, the climate
is not damaging to the Hap and its communications equipment.
At launch, the solar-powered aircraft would be flown up to the
operating altitude during the day, using several electric motors.
Once on station, the number of motors used would be reduced to two
or three to maintain its position; energy stored in fuel cells
would power the motors overnight.
Energy storage is one of the obstacles the Hap project still needs
to overcome. Grace said further development work was needed to
improve the efficiency of the fuel cells and the design of the
communications payload.
He also said further work was required to finalise the design and
technology. "We are still at an early stage - the field only began
in the early 1990s. If you think of the money spent on terrestrial
communications, the Hap industry is very small and undeveloped, and
probably equal to the satellite industry in the 1960s."
Capanina project
The Capanina project began in November 2003 and will run for three
years. It follows on from work done in the Helinet project (2000 to
early 2003), which illustrated the potential of broadband delivery
from high-altitude platforms and came up with an outline system
design.
The University of York's communications research group and physical
layer research group in the electronics department are involved in
the European Commission-funded £3.9m Capanina project.
Capanina will develop a test-bed using low-altitude tethered
craft, stratospheric balloons and an outline design for a system to
deliver 120mbps to on-board wireless Lan on vehicles such as trains
travelling at up to 300km an hour.
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