TOKYO — Buoyed by a recent government study on beaming solar power from space, some Japanese researchers are pushing for a large demonstration spacecraft that would launch around the end of the decade.

The report by the Japanese Ministry of Economy, Trade and Industry (METI) envisions the deployment of increasingly capable stations for solar power beaming in the decades ahead.

The report, "Technical Development and Investigative Report Toward a Practical Space Solar Power System," was released internally at the end of March and made public the week of May 12.

Five years in the making, the report proposes launching an 18,000-kilogram demonstration satellite aboard a proposed heavy-lift variant of Japan’s H-2A rocket to an orbital altitude of about 370 kilometers. The spacecraft, equipped with a large antenna that would double as a solar power collector, would convert that power into microwave energy for transmission to a special ground station.

It is a concept that has been studied for decades but never designed in detail, according to Tetsu Kobayashi, general manager of the METI’s Institute for the Unmanned Space Experiment Free Flyer. The institute is responsible for coordinating METI’s research in space-based solar power.

The proposed demonstration craft would not be of much practical use, proponents acknowledged. For example, its power-beaming capabilities would be limited to the five-minute intervals during which it is passing over its ground station, Kobayashi said. In addition, most of the collected energy would be lost in the conversion and transmission process.

Susumu Sasaki, chairman of the free flyer institute’s Study Team for the Space Solar Power System and the main author of the report, said an operationally useful space solar power beaming system probably would have to be located in geostationary orbit. Geostationary satellites maintain a constant position relative to the Earth’s surface.

"For any commercial system, you are going to need power constantly. But this is a trial system that can be launched for $200 million to $300 million and this sort of simple system is needed to verify the technology," Sasaki said in a May 21 interview. Sasaki said the cost figure excludes the price of the launch.

Patrick Collins, a professor of economics at the Azabu University near Tokyo and a collaborating researcher with Japan’s Institute of Space and Astronautical Science, said the important thing is to fly a working demonstration to prove the viability of the concept.

"The money they are talking here is peanuts to the [power] generation industry, and getting kilowatts of power from a single [rocket] shot is terrific. People have been talking about space solar power for 30 years and the electricity industry has been saying ‘show us a system,’" Collins said.

But the proposed demonstration system faces budgetary hurdles and competition in the form of an alternative approach backed by the National Space Development Agency of Japan or NASDA.

NASDA’s proposal, according to documents released in November 2002, includes an experiment that would demonstrate microwave transmissions between a mother and daughter satellite at the end of the decade.

The plan then moves on to a 10-megawatt test system mounted on the international space station.

Hiroshi Matsumoto, chairman of NASDA’s Space Solar Power Committee, said the two camps almost certainly would find a compromise over the next "year or two." Matsumoto, director of Kyoto University’s Radio Science Center for Space and Atmosphere, is mainly responsible for developing many of the core technologies for microwave power beaming in Japan. "It’s very important to test ideas and … we are all in the same boat," Matsumoto said in a May 17 telephone interview. "I’m pretty optimistic we can merge after [Japan’s] space agencies merge this October."

A senior METI official, who declined to be named, said the Ministry of Finance would never support funding for two separate space solar power plans.

"They [NASDA] are over there, and we are over here. Everyone agrees that this is a national project and everyone sees the same target. Competition isn’t a bad thing and before we launch a verification project of whatever kind, we’ll unify," the official said.