The decision, which was made by a sub-committee within STA late in March, will ask NASDA to conduct a 240 million yen ($1.9 million) research program to develop suitable hydrogen maser atomic clocks and more accurate orbit determination capabilities.

The committee, which met five times from last September, had been asked to discuss five scenarios. The first was to continue to rely on the American GPS and Russian GLONASS systems, the third looked at the development of a regional, independent GPS system, the forth considered linking a regional GPS system with NASDA's inter-satellite communications research program, while the last assessed the possibility of a joint Japanese-European developed GPS system. The committee chose the second, which will implement a program to continue research into developing GPS-related technologies, without committing Japan to the completion of an independent system.

"We've ruled out trying to build an alternative system independently, it'll be too expensive," said Mitsugi Chiba, director of STA's space Policy decision, who said the committee refused to commit funding for full-scale development for mainly budgetary reasons.

"I suppose we'll aim at scenario three or scenario five, either a regional system to augment current GPS, or we'll develop one in cooperation with Europe," said Ryuichi Sekita, deputy director of STA's space policy decision.

The policy change reflected last summer's suspension of more ambitious plans when NASDA had proposed a four-satellite system to be developed via the Mission Demonstration Satellite program (MDS), a small-bus test satellite initiative designed to complement NASDA's current engineering test satellite program from 2000.

That GPS system would have consisted a mini-constellation of one geostationary and three LEO satellites. This proposal had been preceded by an even more ambitious eight 500-700 kg. test satellite constellation which would have been launched between 2002-5, NASDA sources revealed to Japan Space Net last July.

Both plans were stalled following the visit last August of a U.S. delegation, led by the US Assistant Secretary of Defense, which expressed alarm at the moves. Shortly afterwards the Ministry of Foreign Affairs announced that it would temporarily suspend the initiatives and reconsider Japan's options. This month's report seems to have taken the most cautious route, while admitting that Japan feels it must proceed with at least the technological development necessary to develop an independent GPS system.

STA's stance was supported by Japan's Ministry of International Trade and Industry, according to an ministry official who declined to be named.

"Japan must have the technology. While Clinton declared he would maintain the system on an open-use basis, the current GPS system is inaccurate.

"While they say we may have access to the civil codes forever, we have to play safe and we have to secure a system which will cover Japan at all times. We have to maintain GPS services for our economic security. The U.S. still want theirs to be the only [Milspec] GPS system in the world and are very concerned about rival systems, so the STA's report was written to take this into consideration," said the official.

"We haven't decided how to respond to the U.S. and we will be conducting discussions. It'll take about seven years or so to execute the basic technical development," said Sekita, who said STA would use either a future MDS-3 or MDS-4 bus after 2000 to test a future system.

The Ministry of Post and Telecommunications (MPT) had strongly urged STA to adopt the research strategy, said Masao Matsumoto, director of MPT's space communications policy division.

"We were heavily involved in the discussions. STA and NASDA were pushing for a more speedy implementation to develop a preliminary system which could have been turned into a commercial system. They'd shown some preference for a regional system but we have recommended to reconsider. We're very happy with the report," he said.

Matsumoto also said that he thought it would be impossible, at least in the short term, for either Europe or Japan to seriously implement a rival system in the face of strong U.S. pressure. He didn't rule out the possibility of Japan partially paying for a next-generation system led by the U.S. as long as Japan was allowed to contribute hardware.

Aside from political issues, NASDA's first priority will be to improve orbital placement from the present 150-meter accuracy to 10 meters or less, said the report.

"There are three main obstacles, orbit placement accuracy, on-board time accuracy and atmospheric distortion compensation. Of these the first is most important. We need to be able to get the satellite to within one meter of its intended position if we are to meet later positional accuracy requirements," NASDA engineer Jun Gomi told Japan Space Net last summer. Gomi was part of a ten-man team who had drawn up NASDA's original proposals last year.

To achieve the necessary orbit accuracy, NASDA will attempt to develop satellite orbital placement, tracking, and accuracy technology necessary for developing a viable GPS system. ADEOS-2, the successor to the Advanced Earth Observation Satellite, will be positioned within ten meters of its planned orbit by fitting it with a GPS system. Scientists will then try to determine the Advanced Land Observation Satellite's (ALOS) orbit to within one meter via the fitting of a laser ranging device, said Gomi. ADEOS-2 and ALOS are scheduled for launch by H-2As in August 1999 and 2003 respectively.

"We do need these very basic technologies, so we should develop them for the future, then we'll look at the scenarios again," said Chiba.