KAGOSHIMA - The Japan Aerospace Exploration Agency conducted a ground firing test of the second-stage engine for its Epsilon S small solid-fuel rocket at the Tanegashima Space Center in Kagoshima Prefecture on July 23.
JAXA adopted an engine based on an older, proven design for the latest test after a series of explosions involving a newly developed engine.
Epsilon S is Japan's next-generation small satellite launcher, developed as the successor to the Epsilon series of solid-fuel rockets. The program is intended to provide Japan with a more competitive, reliable and flexible way to place small satellites into orbit while preserving the country's independent access to space.
The original Epsilon rocket made its first flight from the Uchinoura Space Center in Kagoshima Prefecture in September 2013. It was developed as a lower-cost successor to the M-V rocket, which had launched Japanese scientific spacecraft but was expensive and labor-intensive to operate. Epsilon introduced extensive computer-based launch checks and automation, reducing the number of personnel and the time required for launch preparations.
An upgraded version, known as the Enhanced Epsilon, was introduced in 2016. Its larger second-stage M-35 motor increased launch capacity and allowed the rocket to carry heavier satellites. The Epsilon family completed five successful launches between 2013 and 2021, carrying scientific and technology-demonstration satellites including Hisaki, Arase and RAISE-2.
The program suffered its first launch failure in October 2022, when Epsilon-6 was ordered to self-destruct after losing control of its attitude during flight. The rocket and eight satellites were lost. An investigation traced the failure to a problem in the second-stage attitude-control system.
Epsilon S was already under development as a more commercially competitive successor. The "S" represents the rocket's aim of creating stronger links between Japan's space program and private-sector satellite operators. JAXA has developed the launcher with IHI Aerospace, which is expected to take a larger role in production and launch services.
The design combines technology from the Enhanced Epsilon with components developed for Japan's larger H3 rocket. Its first stage is based on the H3's SRB-3 solid rocket booster, while new second- and third-stage motors were intended to improve performance, simplify production and reduce costs. JAXA also sought to shorten the period between receiving a satellite and launching it, an important requirement in the growing international small-satellite market.
Development encountered a major setback during a second-stage motor firing test at JAXA's Noshiro Rocket Testing Center in Akita Prefecture on July 14, 2023. The motor exploded less than a minute after ignition, damaging the test facility but causing no injuries. JAXA later concluded that part of the ignition system had melted and scattered, damaging the surrounding propellant and insulation.
After design changes, JAXA conducted another second-stage firing test at the Tanegashima Space Center on November 26, 2024. That motor also exploded, about 49 seconds after ignition during a test that was expected to last roughly 120 seconds. No one was injured, but the repeated failure forced JAXA to reconsider the engine's design and delayed the rocket's first flight.
To accelerate the program's recovery, JAXA abandoned plans to use the newly developed second-stage motor for the initial version of Epsilon S and returned to a design based on the proven M-35 motor used by the Enhanced Epsilon. The change reduces some of the performance improvements originally planned but lowers development risk and draws on an engine with an established flight record.
The revised second-stage motor underwent a ground firing test at the Tanegashima Space Center on July 23, 2026. It burned for approximately two minutes as planned, marking an important step toward the first Epsilon S launch, which JAXA is seeking to conduct during fiscal 2026.
Source: Kyodo
