TANEGASHIMA, October 19, 2026 — The Japan Aerospace Exploration Agency is preparing to launch the Martian Moons eXploration mission, utilizing the H3 rocket in a specialized configuration to carry a 4.48-ton probe toward the Martian system. This mission marks the first operational use of a long fairing on the H3, a significant step in the rocket’s evolution into a versatile vehicle for deep space exploration.
From H-IIA Successor to Modular Platform
The H3 is a medium-lift launch vehicle developed through a collaboration between the Japan Aerospace Exploration Agency (JAXA) and Mitsubishi Heavy Industries. According to JAXA, the rocket was designed to serve as the successor to the H-IIA and H-IIB launch vehicles. Development of the program began in 2013 following formal government approval. The project aimed to create a more efficient and cost-effective platform to support both government and commercial launch markets.
The H3 features a modular design, which allows the vehicle to be adapted for a wide variety of mission profiles. The first stage can be powered by either two or three LE-9 main engines. Furthermore, the rocket can be fitted with zero, two, or four SRB-3 solid rocket boosters. These boosters are also utilized on the Epsilon S small-lift launch vehicle. This flexibility allows JAXA to tailor the rocket’s thrust and payload capacity based on the specific requirements of each mission.
The path to the current configuration was not without challenges. Following the start of development in 2014, the program experienced delays, including a failed maiden flight in March 2023 when the second-stage engine failed to ignite. However, the program reached a significant milestone in February 2024 with the rocket’s first successful flight. The H3 is now intended to support a range of future objectives, including the launch of the HTV-X cargo spacecraft to the International Space Station and the Lunar Polar Exploration Mission.
Engineering the LE-9 for Efficiency
At the heart of the H3’s propulsion system is the LE-9 main engine, which represents a technical departure from previous Japanese launch vehicles. According to JAXA and Mitsubishi Heavy Industries, the engine was designed to reduce manufacturing time, technical risk, and overall launch costs. The engine employs an expander bleed cycle, a combustion method that had been used previously on the upper-stage LE-5A engine but never before on a first-stage engine.
While expander bleed cycles typically struggle to produce high levels of thrust, the LE-9 was engineered to reach 1,471 kN. The development of this engine was one of the most significant challenges of the H3 program. Ground tests of the LE-9 began in April 2017. During qualification tests in May 2020, engineers identified an opening in the combustion chamber wall and a fatigue fracture in the liquid-hydrogen fuel turbopump turbine. These findings necessitated design adjustments, which ultimately shifted the inaugural launch schedule from 2021 to 2023.
The second stage of the rocket uses the LE-5B-3 engine, which is an upgraded version of an engine family that has been in use since the H-I rocket. The integration of these propulsion systems is supported by a network of Japanese industrial partners. IHI Corporation produces the liquid-fuel engine turbopumps and solid-fuel boosters, while Kawasaki Heavy Industries builds the S- and L-type payload fairings. Toray Industries supplies the carbon fiber and synthetic resin used in the booster motor cases and fairings.
Strategic Importance of the Long Fairing
The upcoming Martian Moons eXploration mission utilizes the H3-24L configuration. This specific setup includes four SRB-3 solid rocket boosters and, notably, the first operational use of a long fairing on the H3 rocket. The fairing is an essential component for protecting deep space payloads during the initial ascent through the atmosphere. The inclusion of the long fairing allows the rocket to accommodate larger or more complex instruments required for interplanetary travel.
Beyond the domestic components, the H3 program also incorporates international expertise. The Switzerland-based firm Beyond Gravity manufactures the W-type fairing, which is based on a standard 5.4-metre-wide design also used on the Ariane 6 and Vulcan Centaur rockets. The ability to swap fairing types and adjust booster configurations provides the H3 with the versatility required to compete in the international launch market.
The Martian Moons eXploration probe, which weighs approximately 4.48 tons, represents the kind of complex payload the H3 is designed to carry. By successfully deploying this mission, JAXA aims to collect samples from the Martian moon Phobos and return them to Earth. If the mission succeeds, it will be the world’s first Martian moon sample return mission. The data gathered is intended to help researchers understand the origin of the Martian moons and the formation of the Martian sphere.
Future Outlook for the H3 Program
The H3 is positioned to be a central element of Japan’s space transportation strategy for the coming years. By moving away from the older H-IIA and H-IIB systems, JAXA and Mitsubishi Heavy Industries are aiming to streamline operations and reduce the costs associated with accessing space. The modular nature of the vehicle ensures that it can be adjusted as mission requirements evolve, whether for Earth-orbiting satellites or deep space exploration.
The operational history of the H3, despite early setbacks, shows a focus on iterative improvement. The transition from the failed 2023 attempt to the successful 2024 flight demonstrated the effectiveness of the engineering adjustments made to the propulsion and flight systems. As the program continues, the H3 is expected to maintain its role as a primary vehicle for both scientific discovery and commercial logistics.
The upcoming launch at the Tanegashima Space Center serves as a practical demonstration of these capabilities. By utilizing the H3-24L configuration, JAXA is testing the limits of the rocket’s current design in a challenging interplanetary mission. The success of this launch will likely influence future mission planning for both the Lunar Polar Exploration Mission and other international collaborations. The H3 is now established as a core asset in the effort to maintain a consistent and reliable presence in space.
Sources
- [Note Exclusive] H3 Rocket Flight 15 to Launch the Day After Tomorrow at Dawn; MMX to Unravel the Origin of Martian Moons, Aiming for Phobos Sample Return by 2030｜相模経済新聞
- H3 (rocket)
- JAXA’s Martian Moons eXploration (MMX) Mission Set to Launch Next Tuesday on H3 Rocket – SpaceWatch.GLOBAL
Photo: Hunini (CC BY-SA 4.0)
