Japan's H3 rocket, the flagship launch vehicle of the Japan Aerospace Exploration Agency (JAXA), encountered a significant setback during its eighth mission on 22 December 2025, when the second-stage engine failed to ignite properly, preventing the deployment of the Michibiki No. 5 satellite into its planned geosynchronous orbit.

The launch took place at 10:51 JST from the Yoshinobu Launch Complex at Tanegashima Space Center, marking a disappointing end to what had been a series of recent successes for the rocket.

Telemetry data indicated that pressure in the second-stage hydrogen tank began dropping anomalously during the first-stage engine burn, leading to a first-stage cut-off 27 seconds later than scheduled and a 15-second delay in the second-stage ignition attempt.

The second-stage engine's second burn, intended to last over four minutes, shut down prematurely, rendering the mission a failure and leaving the QZS-5 satellite—also known as QSZ-5—unable to reach its designated orbit. It remains unclear whether the satellite successfully separated from the upper stage.

This incident follows a one-day delay from the original 21 December lift-off, rescheduled after JAXA identified an issue in the frame deflector cooling system of the cooling water injection equipment on 19 December. Verification tests confirmed proper water flow, allowing the attempt on 22 December within a launch window from 10:30 to 11:30 JST, though the reserved period extended to 31 January 2026.

The H3 rocket, standing 63 metres tall and developed over 11 years as a successor to the retired H-2A, has faced challenges since its debut. Its inaugural flight on 7 March 2023 ended in self-destruction 14 minutes and 50 seconds after launch due to a second-stage ignition failure caused by an electrical glitch, resulting in the loss of the $200 million ALOS-3 Earth-observing satellite.

Despite this rocky start, the rocket achieved five consecutive successes prior to this seventh or eighth attempt—sources vary slightly on numbering—demonstrating improved reliability until now.

In response, JAXA has established a special task force led by President Hiroshi Yamakawa to investigate the root cause of the anomaly, expressing apologies to stakeholders, including those involved with QZS-5 and local communities

 The Michibiki series forms Japan's Quasi-Zenith Satellite System, a regional navigation network requiring seven satellites for full coverage, with this being the sixth orbiter.

This failure introduces uncertainty for JAXA's 2026 manifest, which includes another QZS satellite, the HTV-X cargo spacecraft for the International Space Station, and the high-profile Martian Moons eXploration (MMX) mission slated for late 2026.

JAXA aims for at least two H3 launches annually to bolster Japan's independent access to space, but the probe's findings will dictate timelines amid growing competition in the global launch market. The agency plans to provide updates as investigations progress.

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