Epsilon (rocket)

The Epsilon Launch Vehicle, or (formerly Advanced Solid Rocket), is a Japanese solid-fuel rocket designed to launch scientific satellites. It is a follow-on project to the larger and more expensive M-V rocket which was retired in 2006. The Japan Aerospace Exploration Agency (JAXA) began developing the Epsilon in 2007. It is capable of placing a 590 kg payload into Sun-synchronous orbit.

Vehicle description E-X The development aim is to reduce the US$70 million launch cost of a M-V; the Epsilon costs US$38 million per launch. Development expenditures by JAXA exceeded US$200 million.

To reduce the cost per launch the Epsilon uses the existing SRB-A3, a solid rocket booster on the H-IIA rocket, as its first stage. Existing M-V upper stages will be used for the second and third stages, with an optional fourth stage available for launches to higher orbits. The J-I rocket, which was developed during the 1990s but abandoned after just one launch, used a similar design concept, with an H-II booster and Mu-3S-II upper stages.

The Epsilon is expected to have a shorter launch preparation time than its predecessors; a function called "mobile launch control" greatly shortens the launch preparation time, and needs only eight people at the launch site, See figure 6 compared with 150 people for earlier systems.

The rocket has a mass of and is tall and in diameter.Epsilon Launch Vehicle Information

Enhanced Epsilon After the successful launch of the Epsilon first flight (demonstration flight), the improvement plan was decided to handle the planned payloads (ERG and ASNARO-2).

Requirements for the improvement: Apogee ≧ 28700 km (summer launch), ≧ 31100 km (winter launch) of a 365 kg payload Sun-synchronous orbit (500 km) of a ≧ 590 kg payload Larger fairing

Planned characteristics: Height: 26.0 m Diameter: 2.5 m Mass: 95.1 t (Standard) / 95.4 t (Optional 4th stage (Post Boost Stage))

Catalog performance according to IHI Aerospace: Low Earth orbit 250 km × 500 km for 1.5 t Sun-synchronous orbit 500 km × 500 km for 0.6 t

Final characteristics: Height: 26.0 m Diameter: 2.6 m (max), 2.5 m (fairing) Mass: 95.4 t (standard) / 95.7 t (optional)

Epsilon S Block 1 The Epsilon rocket's first stage has a common design with the SRB-A3, the solid rocket booster of H-IIA/B. As the H-IIA family has retired in 2025, continuing the production of SRB-A3 solely for Epsilon would lead to a significant rise in production cost. Thus a new Epsilon variant, the Epsilon S Block 1 which incorporates commonized parts with the H3, the H-IIA's successor, has been in development. The Epsilon S Block 1's first stage will have a common design with SRB-3, the H3's solid rocket booster.

Major changes from Enhanced Epsilon to Epsilon S Block 1 are: The first stage is based on SRB-3, the strap-on solid rocket booster of H3. The third stage designated the E-31 is a new design, whereas Enhanced Epsilon's third stage was based on the M-V's third stage. New third stage is three-axis stabilized, whereas Epsilon's third stage was spin-stabilized. Also the third stage is outside the fairing, whereas Enhanced Epsilon's fairing covered the third stage. The Epsilon S Block 1's fourth stage, the Post Boost Stage (PBS) is mandatory, whereas Enhanced Epsilon's PBS was optional. Epsilon S Block 1's second stage, the M-35a will have the same performance as Enhanced Epsilon's M-35, but with changes in propellant and insulation.

In June 2023, a ground test of the E-31 was conducted at JAXA's Noshiro Rocket Testing Center. Ground testing of the M-35a is scheduled to be conducted in 2026 at the Tanegashima Space Center.

Epsilon S In order to further increase the payload capacity of Epsilon, the Epsilon S Block 1's second stage M-35a is planned to be replaced with a larger solid-rocket motor designated E-21.

Initially, the E-21 was to be introduced simultaniously with the SRB-3 first stage and E-31 third stage. However, on 14 July 2023, a test firing of the E-21 failed. The root cause was determined to be the "melting and scattering of a metal part from the ignition device", which damaged the propellant and insulation. Corrective measures were implemented and the rocket motor was tested again on 26 November 26 2024; however, the second test also resulted in a failure 49 seconds after ignition.

In July 2025, NHK reported that JAXA was reviewing its development plans for the Epsilon S. In order to move up plans for a return to flight, the decision was made to defer planned improvements to the second stage and revert to using the proven, existing design of Enhanced Epsilon. While this would entail performance being lower than originally planned, it could enable a launch as early as late 2026.

Launch statistics Launch outcomes

Launch history Epsilon launch vehicles are launched from a pad at the Uchinoura Space Center previously used by Mu rockets. The first flight, carrying the SPRINT-A scientific satellite, lifted off at 05:00 UTC (14:00 JST) on 14 September 2013. The launch was conducted at a cost of US$38 million.

On 27 August 2013, the first planned launch of the launch vehicle had to be aborted 19 seconds before liftoff because of a botched data transmission. A ground-based computer had tried to receive data from the launch vehicle 0.07 seconds before the information was actually transmitted.

The initial version of Epsilon, E-X had a payload capacity to low Earth orbit of up to 500 kilograms, with the Enhanced Epsilon expected to be able to place into a orbit, or to a circular orbit at with the aid of a hydrazine fueled stage.

Flight No. Date / time (UTC) Configuration Payload Payload mass Orbit Customer Outcome 1 14 September 201305:00:00 E-X, 4 stage SPRINT-A (HISAKI) 340 kg LEO JAXA Demonstration Flight 2 20 December 201611:00:00 Enhanced, 3 stage ERG (ARASE) 350 kg Geocentric JAXA 3 17 January 201821:06:11 Enhanced, 4 stage ASNARO-2 570 kg SSO Japan Space Systems 4 18 January 201900:50:20 Enhanced, 4 stage RAPIS-1MicroDragonRISESATALE-1OrigamiSat-1AOBA-VELOX-IVNEXUS 200 kg SSO JAXA Innovative Satellite Technology Demonstration-1; component demonstration and technology validation. A new Guidance and Control system was developed for multiple payload deployment capability. 5 9 November 202100:55:16 Enhanced, 4 stage RAISE-2HIBARIZ-SatDRUMSTeikyoSat-4ASTERISCARICANanoDragonKOSEN-1 110 kg SSO JAXA Innovative Satellite Technology Demonstration-2. 6 12 October 2022 00:50:00 Enhanced, 4 stage RAISE-3QPS-SAR 3QPS-SAR 4MAGNAROMITSUBAKOSEN-2WASEDA-SAT-ZEROFSI-SAT 110 kg SSO JAXA, iQPS RAISE-3 and the six CubeSats were part of Innovative Satellite Technology Demonstration-3. QPS-SAR 3/4 were Epsilon's first commercial satellites launch contracts. Vehicle was destroyed by flight termination system shortly after second stage cutoff due to an attitude control fault. A report regarding the cause has been published and is available for viewing, although it is in Japanese.

Planned launches Launch (UTC) Configuration Payload Orbit Customer 2026 Epsilon S Block 1 TBD TBD JAXA TBD Epsilon S Block 1 LIDAR Altimeter Satellite SSO JAXA TBD Epsilon S Block 1 TBD (JAXA-STEPS rideshare) TBD JAXA TBD Epsilon S Block 1 LOTUSat-1 SSO VNSC July 2028 Epsilon S Solar-C SSO JAXA November 2028 Epsilon S with Kick Stage OPENS-0 TBD JAXA 2032 Epsilon S JASMINE SSO JAXA

Sources: Cabinet Office of Japan

Internet data leak In November 2012, JAXA reported that there had been a possible leak of rocket data due to a computer virus. JAXA had previously been a victim of cyber-attacks, possibly for espionage purposes. Solid-fuel rocket data potentially has military value, and Epsilon is considered as potentially adaptable to an intercontinental ballistic missile. The Japan Aerospace Exploration Agency removed the infected computer from its network, and said its M-V rocket and H-IIA and H-IIB rockets may have been compromised.

Epsilon (rocket)

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