H-IIB

When JAXA became a member of the ISS builder nations, one of the things it was tasked with is the resupply of the station. To do this, the scientists and engineers have developed the HTV Kounotori - an automated spaceraft to deliver supplies, equipment and experiments to the station. They however faced a problem - the spacecraft couldn't fit in the fairing of the H-IIA or the H-II rockets, and even if it could, they wouldn't be able to throw it into space reliably. To counter this, Mitsubishi was tasked to develop a new system, with as much part commonality as possible without sacrificing payload capacity or reliability.

The rocket, now called H-IIB, had many similarities to the H-IIA, but with two key differences: the first stage was now 5.4 meters wide to accomodate the extra fuel needed, and the first stage was now powered by two LE-7A engines, compared to one on the H-II and H-IIA. The second stage remained the same, a 2m wide hydrolox rocket stage powered by an expander-cycle LE-5B engine. All of this made the rocket capable of lifting 18 tons to LEO and 8 tons to GTO - twice as much as the H-IIA.

The rocket launched 9 times, every time successfully. Every flight carried a Kounotori spacecraft. The last time the rocket flew was in 2020 - after that, it was replaced by a far more advanced H-3.

Heads Up!
This craft uses a hinge booster separation mechanism, like in real life. Stage once to activate the mechanism, wait a second, stage once again to release the boosters