# Epsilon (rocket)

The Epsilon Launch Vehicle, or Epsilon rocket (イプシロンロケット, Ipushiron roketto) (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

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 91 t (90 long tons; 100 short tons) and is 24.4 m (80 ft) tall and 2.5 m (8 ft 2 in) in diameter.

### Enhanced version

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

Epsilon's first stage has been the modified SRB-A3 which is the solid-rocket booster of H-IIA. As the H-IIA is to be decommissioned and to be replaced by H3, Epsilon is to be replaced by a new version, named 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 (PBS), 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.
Planned performance of Epsilon S is:
* Sun-synchronous orbit (350 – 700 km): ≧ 600 kg
* Low Earth orbit (500 km): ≧ 1400 kg
The first launch of Epsilon S is planned in 2023.
On July 14, 2023, the solid-fuelled second stage of Epsilon S failed during a test firing. 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 stage was tested again on November 26, 2024; however, the second test also resulted in a failure 49 seconds after ignition.

## Launch statistics
### Launch outcomes

* Failure
* Partial failure
* Success
* Planned

## 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 (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 has a payload capacity to low Earth orbit of up to 500 kilograms, with the operational version expected to be able to place 1,200 kg (2,600 lb) into a 250 by 500 km (160 by 310 mi) orbit, or 700 kg (1,500 lb) to a circular orbit at 500 km (310 mi) with the aid of a hydrazine fueled stage.
| Flight No. | Date / time (UTC) | Rocket, Configuration | Launch site | Payload | Payload mass | Orbit | Customer | Launch outcome |
| 1 | 14 September 2013 05:00:00 | Epsilon 4 Stages | Uchinoura Space Center | SPRINT-A (HISAKI) | 340 kg | LEO | JAXA | Success |
| Demonstration Flight ||||||||
| 2 | 20 December 2016 11:00:00 | Epsilon 3 Stages | Uchinoura Space Center | ERG (ARASE) | 350 kg | Geocentric | JAXA | Success |
| 3 | 17 January 2018 21:06:11 | Epsilon 4 Stages | Uchinoura Space Center | ASNARO-2 | 570 kg | SSO | Japan Space Systems | Success |
| 4 | 18 January 2019 00:50:20 | Epsilon 4 Stages | Uchinoura Space Center | RAPIS-1 MicroDragon RISESAT ALE-1 OrigamiSat-1 AOBA-VELOX-IV NEXUS | 200 kg | SSO | JAXA | Success |
| Innovative Satellite Technology Demonstration-1; component demonstration and technology validation. ||||||||
| 5 | 9 November 2021 00:55:16 | Epsilon PBS | Uchinoura Space Center | RAISE-2 HIBARI Z-Sat DRUMS TeikyoSat-4 ASTERISC ARICA NanoDragon KOSEN-1 | 110 kg | SSO | JAXA | Success |
| Innovative Satellite Technology Demonstration-2. ||||||||
| 6 | 12 October 2022 00:50:00 | Epsilon 4 Stages | Uchinoura Space Center | RAISE-3 QPS-SAR 3 QPS-SAR 4 MAGNARO MITSUBA KOSEN-2 WASEDA-SAT-ZERO FSI-SAT | 110 kg | SSO | JAXA, iQPS | Failure |
| 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

| Date / time (UTC) | Rocket, Configuration | Launch site | Payload | Orbit | Customer |
| 2024 | Epsilon S | Uchinoura Space Center | LOTUSat-1 | SSO | VNSC |
| 2025 | Epsilon S | Uchinoura Space Center | Innovative Satellite Technology Demonstration-4 | LEO | JAXA |
| 2027 | Epsilon S | Uchinoura Space Center | Innovative Satellite Technology Demonstration-5 | LEO | JAXA |
| July 2028 | Epsilon S | Uchinoura Space Center | Solar-C EUVST | SSO | JAXA |
| 2028 | Epsilon S | Uchinoura Space Center | JASMINE | SSO | JAXA |
| 2029 | Epsilon S | Uchinoura Space Center | Innovative Satellite Technology Demonstration-6 | LEO | JAXA |
| 2030 | Epsilon S | Uchinoura Space Center | HiZ-GUNDAM [ja] | SSO | JAXA |
| 2031 | Epsilon S | Uchinoura Space Center | Innovative Satellite Technology Demonstration-7 | LEO | JAXA |
Sources: Japanese Cabinet

## 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.