Japan’s Epsilon S Rocket Suffers Another Setback

Japan’s efforts to develop the Epsilon S rocket suffered another setback when the engine exploded during a test on Tuesday (Japan time).  A test last year ended the same way. Epsilon S is an improved version of the Epsilon small rocket in development for almost two decades by JAXA and IHI Industries to compete on the world market for launches of cubesats and other small satellites.

The Epsilon family is a follow-on to the M-V series that operated from 1997-2006. The goal is to develop a less costly rocket that can be commercially competitive in the small rocket class.

Five successful launches of the original version of Epsilon took place from Japan’s Uchinoura launch site between 2013 and 2021. A sixth in 2022 failed.

JAXA and IHI began development of Epsilon S in March 2020, but a test of the second stage engine in July 2023 ended in an explosion because of excessive heat that melted and scattered a metal part. Tuesday’s test at Japan’s main launch site on Tanegashima was intended to demonstrate the problems had been resolved.

The test began at 8:30 am November 26 Japan Standard Time (6:30 pm November 25 Eastern Standard Time). Scheduled for two minutes, it exploded at 49 seconds due to a “combustion abnormality.” No one was injured.

Japan’s Chief Cabinet Secretary Yoshimasa Hayashi said during a press conference that JAXA would conduct a thorough investigation and emphasized the importance of the rocket’s development to Japan. “Epsilon S rockets and the core rocket development is important for autonomous space development for Japan. This is crucial for our country going forward. JAXA is going to start investigations and also take countermeasures thoroughly.”

Kyoto News quoted JAXA Project Manager Takayuki Imoto as apologizing for not meeting expectations and “We will take advantage of this opportunity to develop a more reliable rocket.”

If today’s test had been successful, the first launch was scheduled before the end of Japan’s fiscal year on March 31, 2025.

Japan recently introduced a new version of its much larger rocket, H3, which will replace the H-II. The H3 failed on its first launch in 2023, but has had three successes since then.

JAXA explains they added the “S” for this new version on Epsilon to represent “Strengthening its international competitiveness” through “Synergy with H3, Speed of response, Smart in performance, Superior in competitiveness, and Service of launch.”