Japan GPS satellites cut from 7 to 4

JAPAN - The Japanese version of the Global Positioning System likely will operate with four satellites-not the initially planned seven--to save money, although this will not reduce the system's accuracy, space development officials said Tuesday.

At least seven Japanese quasi-zenith satellites were previously thought to be necessary to configurate a complete system that would not have to depend on a similar system of the United States.

However, the Strategy Headquarters for Space Development has decided four satellites will be sufficient to identify an object's position on Earth with a high degree of accuracy, the officials said.

Japan launched its first quasi-zenith satellite, Michibiki, in September last year.

However, funding six more such satellites will be difficult while money is needed for restoration work in areas hit by the Great East Japan Earthquake.

By supplementing and reinforcing the U.S. system, the Japanese version will be 10 times more accurate than current positioning information. Having four satellites will ensure signals can better reach locations in mountainous regions and areas surrounded by high-rise buildings.

Michibiki can be used only for eight hours a day--the time it is in orbit above Japan. With three more satellites in the sky, the four satellites can be used in turn to provide a highly accurate positioning system around-the-clock.

The headquarters estimates a seven-satellite system would require about another 230 billion yen (S$3.5 billion). A four-satellite system is expected to cut this to about 150 billion yen (S$2.3 billion).

The headquarters' special investigation division plans to appropriate funds for developing quasi-zenith satellites in a 2012 budget.

The headquarters, which is headed by Prime Minister Naoto Kan, will make a final decision on the number of satellites as early as this summer, the officials said.