Epsilon (rocket)
The Epsilon Launch Vehicle, or Epsilon 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 began developing the Epsilon in 2007. It is capable of placing a 590 kg payload into Sun-synchronous orbit.
Vehicle description
The development aim is to reduce the US$70 million launch cost of an 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, compared with 150 people for earlier systems.
The rocket has a mass of and is tall and in diameter.
Enhanced version
After the successful launch of the Epsilon first flight, the improvement plan was decided to handle the planned payloads.Requirements for the improvement:
- Apogee ≧ 28700 km, ≧ 31100 km of a 365 kg payload
- Sun-synchronous orbit of a ≧ 590 kg payload
- Larger fairing
- Height: 26.0 m
- Diameter: 2.5 m
- Mass: 95.1 t / 95.4 t
- Low Earth orbit 250 km × 500 km for 1.5 t
- Sun-synchronous orbit 500 km × 500 km for 0.6 t
- Height: 26.0 m
- Diameter: 2.6 m, 2.5 m
- Mass: 95.4 t / 95.7 t
Epsilon S
Major changes of Epsilon S from Epsilon are:
- The first stage is based on SRB-3, the strap-on solid-rocket booster of H3.
- The third stage is a new design, whereas Epsilon's third stage was based on the M-V's third stage. New third stage is three-axis stabilized using Post-Boost Stage, whereas Epsilon's third stage was spin-stabilized. Also the third stage is outside the fairing, whereas Epsilon's fairing covered the third stage.
- The Epsilon S Post-Boost Stage is mandatory, whereas Epsilon's PBS was optional.
- Sun-synchronous orbit : ≧ 600 kg
- Low Earth orbit : ≧ 1400 kg
In July 2025, NHK reported that JAXA was reviewing its development plans for the Epsilon S. In order to expedite the first launch, it was proposed to defer planned improvements to the second stage and revert to using the proven, existing design of Epsilon. While this would entail performance being lower than originally planned, it could enable a launch around the end of 2026 at the soonest.
Due to delays with the development of Epsilon S, the RAISE-4 spacecraft and 8 small satellites originally planned for launch on Epsilon S was moved to launch over 2 launches by Rocket Lab's Electron rocket in December 2025 and Q1 2026 respectively.
Launch statistics
Launch outcomes
Launch history
Epsilon launch vehicles are launched from a pad at the Uchinoura Space Center previously used by Mu launch vehicles. The maiden flight, carrying the SPRINT-A scientific satellite, lifted off at 05:00 UTC 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 has a payload capacity to low Earth orbit of up to 500 kilograms, with the operational version expected to be able to place into a orbit, or to a circular orbit at with the aid of a hydrazine fueled stage.