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Japan plans to develop a more powerful version of its H-IIA rocket to increase its payload for flights to the International Space Station by attaching an extra main engine to the craft, sources in the government and the National Space Development Agency of Japan said Saturday.

The improvement was chosen because the cost will be nearly 10 percent less than that for enhancing the H-IIA’s payload with a liquid rocket booster, an idea currently being considered by NASDA, they said.

Japan is likely to drop the LRB method plan, which was to enter the experimental phase in fiscal 2005, and formally adopt the new plan around June, after deliberations within the Space Activities Commission, they said.

Conventional H-IIA rockets can carry a cargo of up to 4 tons, but the improved version will be able to lift 6 tons, according to the sources.

Two LE-7A main engines will be attached to the first stage of the rocket, which will have a diameter of 5 meters — 1 meter more than conventional H-IIA rockets — enabling it to hold about 50 percent more liquid fuel.

When the rocket carries into orbit a transfer vehicle that carries supplies to the station, four SRB-A solid rocket boosters will be added to the main engines, they said.

Japan, however, plans to continue using conventional H-IIA rockets to put satellites into orbit.

Japan launched two H-IIA rockets last August and in February this year. An experimental device was not put into orbit in the February launch after the unit was discovered to have been incorrectly wired.

The H-IIA is an improved version of the H-II. Two H-II launches ended in failure in February 1998 and November 1999, putting the future of Japan’s space development program in doubt.

The International Space Station project is in danger of becoming strapped for cash after the United States said it would reduce its budget for the program.

The U.S. and Europe expect Japan to develop a feasible way to transport supplies to and from the space station. The reduced cost of the proposed new H-IIA would help bring down the total cost of the space station program, the sources said.

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