TOKYO-The Japanese government is funding research for a 1 trillion yen (US$6.85 billion) Skynet project, scheduled to be ready for commercial launch in 2002, that would use up to 200 airships floating in the stratosphere as base stations for cellular networks.
While the Iridium mobile satellite system (MSS) project is about to be launched and other MSS systems are scheduled to begin services in 1999, the retro airship technology may provide a challenge to advanced satellite systems in the next century.
The system of airships, which would be launched to an altitude of 20 kilometers above the Japanese islands, is being planned to relieve cellular base-station congestion in metropolitan areas of Japan. The government says the airships also could be used as base stations for next-generation multimedia communications, as well as to monitor the global environment.
Proponents say airships are more beneficial than satellites because they are cheaper and can transmit a much larger amount of data, including motion pictures. In addition, according to project planners, cellular phone users using Skynet would be able to communicate with a smaller terminal than an MSS terminal-possibly as small as a wristwatch. Each airship would be designed to serve 20,000 channels.
The Japanese Ministry of Posts and Telecommunications (MPT) and the Science and Technology Agency (STA) are promoting this project and jointly have allocated 900 million yen (US$6.17 million) for 1998 to promote the project’s first-phase studies.
Japan hopes a company or companies will launch commercial service based on technology developed by the government research.
The project will comprise three phases:
The first phase, scheduled to be completed by mid-1999, will involve launching a small, 30-meter airship to an altitude of 300 meters. Using the experimental airship, scientists will study airship design, technology for using millimeter wave band and sensors.
In the second phase, scheduled to be completed by mid-2001, a 100-meter airship will be launched to an altitude of 17 kilometers.
In the third phase, to be completed by mid-2002, a prototype 200- to 300-meter airship will be launched to an altitude of 20 kilometers.
The stratosphere, especially at the altitude of 20 kilometers, was chosen because conditions there are stable all through the year. The average wind velocity at that altitude is 20 meters per second-though it changes depending on the season and on the location.
The airship for commercial launch is scheduled to be 270 meters long and equipped with a one-ton communication mission. Using a global positioning system, the airship will maintain the same position over the Japanese islands. When it is blown off position by wind, it will recover the original position by spinning a propeller, using energy generated by solar panels. The airships would be brought down every couple of years for maintenance by releasing air from the ship.
Takao Arai, deputy director of MPT’s Satellite Mobile Communications Division, admitted it is quite difficult to develop the technology necessary for this project. “This is a completely new concept of airship,” he said. For example, conventional airships use fossil energy, such as oil or coal, and float at 200 meters in height-compared with using solar energy for an airship all the way up at 20 kilometers.
When the system is completed, Arai said, it will provide great advantages to both users and operators of cellular. For example, since it uses an extremely high frequency (EHF) or millimeter wave band, it enables data to be sent at up to 25 Megabits per second.
Another advantage compared with satellites is that construction and maintenance costs would be much lower. The construction cost per airship is 4-5 billion yen (US$27.4 million – US$34.3 million), about one-fourth to one-tenth the cost of a geostationary satellite, according to the MPT.
If 200 airships are launched, the total cost would be 1 trillion yen (US$6.85 billion). The government says projected revenue for a company launching commercial service would be 3 trillion yen (US$20.56 billion).
