Japan’s proposed H-X rocket program is moving ahead, with country’s space agency calling for a private company to develop, build and operate the family of space launchers.

Mitsubishi Heavy Industries, prime contractor and operator of the current H-IIA and H-IIB launchers, is the only conceivable supplier for the H-X, which will presumably be given the permanent name H-III when full-scale development begins.

In calling for a prime contractor for “our new flagship launch vehicle,” the Japan Aerospace Exploration Agency (JAXA) notes that the program depends on funding being available in the national budget for the fiscal year beginning on April 1.

The first H-X, of a version without side-mounted boosters, will be launched in fiscal 2020, lofting a satellite to Sun-synchronous orbit, the agency told the science ministry in December. The second launch, with boosters, will be made a year later and will place a satellite in geostationary orbit.

Several objectives have been driving the H-X program, including a lower operating cost than that of the H-IIA and optimization for reduced throw-weights to Sun-synchronous orbit. JAXA and Mitsubishi Heavy Industries also want a shorter interval between booking and launch than the H-II’s 18 months, and a softer ride for the payload.

A key issue is the need to train young engineers with a development program before their mentors—the developers of the H-II—retire. The latter factor led Mitsubishi Heavy Industries to recommend 2020 as the target for a first launch.

The technological centerpiece of the program is the LE-X, a first-stage engine burning liquid hydrogen with liquid oxygen and using an inherently safe process called expander-bleed to drive the propellant pumps. The first-stage core of the H-X will have two such engines, each generating 145 metric tons of thrust in a vacuum with specific impulse of 432 sec., the latter being a measure of fuel economy. Development began in 2008; confirmation of the engine’s performance and reliability has been a precondition on going ahead with development of the H-X airframe.

Two years ago JAXA told Aviation Week it wanted to concentrate on two main markets for the H-X: lofting 2.5 metric tons to Sun-synchronous orbit without boosters; and, with boosters, 6 tons to geostationary transfer orbit, equivalent to about 15 tons to low Earth orbit. The H-X will be more powerful than those figures imply, however, because they assume launch from Japan’s Tanegashima spaceport, which has a high latitude of 31 deg. and has inhabited islands downrange, forcing the launcher to maneuver during its ascent. Launched from an ideal equatorial base, the boosted H-X would be able to throw perhaps 20 tons to low Earth orbit.