H3-30

The Japanese government approved the H3 programme on 17 May 2013 and detailed development began in 2014, with Mitsubishi Heavy Industries as prime contractor and JAXA as partner on the propulsion system. The key to lowering costs was the new LE-9 engine, which uses an expander bleed cycle, a combustion method previously used only on upper-stage engines such as the LE-5A and never before on a first stage. As early as 2015 JAXA planned to debut the rocket in precisely the H3-30 configuration, without solid boosters, and to fly the booster-equipped version afterwards.

Those plans were reversed. The first launch attempt, on 17 February 2023, was aborted shortly before ignition of the SRB-3 boosters even though the main engines had already lit. The second attempt, on 7 March 2023, ended in failure: the second-stage engine did not ignite and JAXA commanded destruction of the vehicle and the ALOS-3 satellite. After the investigation and corrective measures, the second test vehicle flew successfully on 17 February 2024. The H3-24 configuration debuted on 26 October 2025 with the first HTV-X cargo mission to the International Space Station, and an H3-22S failed on 22 December 2025 in what JAXA attributed to a failure of the payload support structure after fairing separation.

Flight F6, the first of the H3-30 configuration, was delayed after defects were found during a captive firing test in July 2025. It finally lifted off on 12 June 2026 in the H3-30S variant, returning the H3 to flight and placing JAXA's fifth Vehicle Evaluation Payload, VEP-5, into orbit alongside rideshares PETREL, STARS-X, BRO-22, VERTECS, HORN-L and HORN-R. It was Japan's first launch of an all-liquid-propellant orbital rocket and the first rocket whose engines use only the expander bleed cycle.