Full-scale development of Japan’s next major space launcher will begin on April 1, following the formal, and expected, selection of Mitsubishi Heavy Industries (MHI) as prime contractor.

Chosen by the Japan Aerospace Exploration Agency (JAXA), MHI will develop, build and operate the rocket, which will be based on the current H-IIA and related H-IIB series, according to MHI and JAXA. A new engine fueled by liquid hydrogen, the LE-X, has been under development as the technological foundation for a replacement for the H-II series, which has been criticized as too expensive.

The new launcher, which has been called H-X during its predevelopment phase and will presumably be named H-III in service, “will be internationally competitive, incorporating a wealth of the latest technologies and simultaneously achieving supreme reliability and a low cost structure, for full-scale entry into the market for satellite launch services,” MHI says. JAXA says costs for the launcher will be cut by half. The first launch is scheduled for 2020.

Variable combinations of solid-fueled boosters—from none to six—will be used to suit various missions, with throw weights to geosynchronous transfer orbit of 2 to 6.5 tons.

MHI has been operating the H-IIA since 2007 and the more powerful, but rarely used H-IIB since last year. With that background, the choice of MHI as prime contractor for the new launcher has been a formality.

“Leveraging its selection as prime contractor on the new national project, going forward MHI aims to play an even larger role in the establishment of the industrial base to support Japan’s autonomous space activities, and to further enhance its presence in the satellite launch services market worldwide,” the company says in a statement.

The ambitions of JAXA and MHI appear to have diminished somewhat over the past few years. As recently as 2011, JAXA suggested the rocket would be a wholly new replacement for the H-II. Yet even now, the connection with the H-II is unclear, since JAXA says the airframe diameter will be 4.5 to 5 meters (14.8 ft. to 16.4 ft.); a close derivative would almost always use the diameter of the core first-stage of its predecessor, to minimize manufacturing costs. The H-IIA has a first and second-stage diameter of 4 meters; for the H-IIB the figure is 5.2 meters for the first stage and 4 meters for the second.

Height, a more easily variable dimension, will be about 60 meters, JAXA says. Official drawings show constant diameter from the first stage to the payload fairing.