Commercial Rockets

H — Japan, 1986

The original H-I was built by Mitsubishi based on a Thor first stage. The successor H-II was all-Japanese. It was replaced with the cheaper and more reliable H-IIA in 2001, and in 2007 it was privatized, so Mitsubishi has full ownership. The H-IIB arrived in 2009, featuring a fatter first stage with two engines. The prior model remains in use for lighter loads.

Japan had a lot of smaller rockets as they gradually built up their expertise, mostly named after letters of the Greek alphabet. Now those are all gone, except that they’ve gone back to that in naming the new Epsilon.

The core stage burns hydrogen, and is augmented with either two or four stubby solid boosters, sometimes with even smaller booster-ettes tucked in between. The H-IIB always uses four, as its whole point is for heavier lifting than the A. The second stage also burns hydrogen.

There were a couple of different plans to launch human beings on an H-IIA, with both capsule and spaceplane designs existing on paper, but none were built.

They are now working on an H-III. (They’re also working on saying “H3” instead of using roman numerals.) For this they’re replacing the dual LE-7A hydrogen engine with either two or three new engines called LE-9. The old engine used staged combustion, but for the new one they are building the world’s biggest expander-cycle engine, apparently on the belief that higher reliability matters more than higher specific impulse. Even with just two engines, this will increase the stage’s thrust considerably. The LE-5B expander on the second stage is getting a small upgrade. The III will have smaller solid boosters than the IIB used. Otherwise, not much has changed, so the cost is not likely to be reduced all that much. As this neared readiness, the IIB was retired, while the IIA remains active.