Japan's New Configuration H3 Launch Vehicle Encounters Development Difficulties

The Japan Aerospace Exploration Agency (JAXA) reported at a meeting of the Ministry of Education, Culture, Sports, Science and Technology's Space Development Utilization Expert Panel on the 29th that the H3 Launch Vehicle No. 6 experienced a failure during an engine combustion test in July this year. The launch, originally scheduled for within this fiscal year, may not proceed as planned.

The H3 launch vehicle is Japan's next-generation mainstay rocket, jointly developed by JAXA and Mitsubishi Heavy Industries. The five previously launched H3 rockets were all of the "22S" configuration, meaning the first stage's main propulsion consisted of two liquid-fueled LE-9 expander cycle hydrogen-oxygen engines, supplemented by two solid rocket boosters. However, the H3 Launch Vehicle No. 6 uses a new "3-0" configuration, employing three liquid-fueled main engines without any boosters. This would mark Japan's first launch of a large liquid-fueled launch vehicle without boosters.

According to reports from media outlets such as Kyodo News and the Sankei Shimbun, JAXA reported on the 29th that during the July static firing test of the first stage for the No. 6 vehicle's "3-0" configuration, while sufficient operational data for the vehicle and equipment were obtained, a failure occurred where the hydrogen and oxygen fuel tank pressures did not meet standards, making it difficult to supply sufficient fuel to the main engines. Resolving this issue and conducting a new static firing test will require time, potentially preventing the No. 6 vehicle's launch within the originally planned 2025 fiscal year (April 2025 to March 2026).

JAXA stated that the aforementioned issue is specific to the "3-0" configuration and does not affect the H3 Rocket No. 7, which uses solid rocket boosters. No. 7 is still scheduled for launch in late October this year.

During the same meeting, JAXA also reported on the status of the small solid-fuel rocket "Epsilon S" currently under development. During a second-stage engine combustion test conducted in November 2024, this rocket experienced abnormal combustion and a fire. The agency said that as identifying the cause will require considerable time, it is considering altering the development plan by changing the second-stage engine for "Epsilon S" from the under-development E-21 to the M-35 engine used by its predecessor, the "Enhanced Epsilon."