Space station partners assess logistics needs beyond 2015 [Spaceflight Now]

Japanese officials may also ask for funding to fly extra HTVs to the station, but their request may face steeper opposition.

"We hope to increase the budget for the researchers and also the H-2B and HTV for the future of our space missions. Right now, we are discussing in the Japanese government about the future plan of our next generation for future exploration and also the ISS extension," said Naoki Nagai, deputy director of the Japanese space agency's Houston office.

A Japanese government panel has singled out the country's space program for potential budget cuts. The Government Revitalization Unit spent more than a week screening budget requests of Japanese government agencies and advised reducing funding by 10 percent for the HTV program.

The tight budget environment could make it difficult for Japanese space officials to expand the agency's mission portfolio, including adding more HTV missions or upgrading the spacecraft.

The unit price tag for each HTV is around $200 million, excluding the cost of the H-2B rocket. An ATV spacecraft costs about $300 million, not including the Ariane 5 rocket or mission costs.

ISSが2015年以降も運用される事になった場合HTVやATVも増便される事になるだろうというという話ですが、先の事業仕分けでHTV関連について10%の縮減要求が出た事に言及し、予算の緊縮により今後のHTV運用計画に影響が出る事を懸念しているようです。