SRB-A
Family of Japanese solid rocket boosters
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The SRB-A and SRB-3 are a family of Japanese solid-fueled rocket boosters developed and manufactured by IHI Corporation for use on the H-IIA, H-IIB, Epsilon, H3, and Epsilon S launch vehicles. The earlier versions, designated SRB-A, flew from 2001 to 2025, while the successor SRB-3 made its first flight in 2023.
Closeup of the SRB-A attached to the H-IIA rocket which launched the Global Precipitation Measurement spacecraft | |
| Manufacturer | IHI Corporation |
|---|---|
| Country of origin | Japan |
| Used on | |
| SRB-A | |
| Height | 14.6 m (47 ft 11 in) |
| Diameter | 2.5 m (8 ft 2 in) |
| Gross mass | 75.5 t (166,449 lb) |
| Propellant mass | 66.8 t (147,269 lb) |
| Maximum thrust | 2,300 kN (517,061 lbf) |
| Specific impulse | 283.6 s (2.781 km/s) |
| Burn time | 110 seconds |
| SRB-3 | |
| Height | 15.1 m (49 ft 6 in) |
| Diameter | 2.5 m (8 ft 2 in) |
| Gross mass | 76.6 t (168,874 lb) |
| Propellant mass | 66 t (145,505 lb) |
| Maximum thrust | 2,158 kN (485,138 lbf)[1] |
| Specific impulse | 283.6 s (2.781 km/s)[2] |
| Burn time | 116 seconds[2] |
Design
All SRB variants have a composite motor case constructed from carbon-fiber-reinforced polymer materials, with thrust vector control provided by electrically actuated nozzles. IHI led development and production, with contributions from other Japanese manufacturers: the composite propellant (BP-208) was developed by NOF Corporation, and the T1000GB carbon fiber used in the motor case was developed by Toray.[3]
The SRB-A motor case incorporated foreign technology licensed from Alliant Techsystems (ATK), based on the Castor 120 motor used in the LGM-118 Peacekeeper ICBM.[4] By contrast, the SRB-3 uses a fully domestic motor case design developed in Japan.[5]
SRB-A series
The SRB-A was developed for the H-IIA rocket and first flew in 2001. It was later used on the larger H-IIB and as the first stage of the smaller Epsilon rocket. It measured 2.5 metres (8 ft 2 in) in diameter and 15.1 metres (50 ft) in length, with a filament-wound composite casing. It replaced the SRBs used on the earlier H-II rocket.[6]
Variants
- SRB-A — The initial version, used on the first six H-IIA launches. A separation failure on the sixth launch in 2003 led to loss of mission.[6][7]
- SRB-A2 — A planned upgrade canceled after the 2003 failure; its design changes were merged into the SRB-A Improved.
- SRB-A Improved — Incorporated a redesigned bell-shaped nozzle to reduce erosion, with slightly lower thrust and longer burn time. Used on the seventh through thirteenth H-IIA flights, but nozzle erosion persisted.
- SRB-A3 — Final SRB-A version, with further improvements to reliability and performance. Available in a high-thrust or long-burn variant. Used on all H-IIA launches after the thirteenth flight, as well as on the H-IIB and as the first stage of the Epsilon rocket.[6][8][9]
The SRB-A series was retired in 2025 and replaced by the SRB-3.
SRB-3
The SRB-3 is the current generation of Japanese solid rocket boosters, developed for the H3 and Epsilon S launch vehicles. Compared to the SRB-A, it carries 1 tonne (2,200 lb) more propellant, uses a fixed nozzle, and incorporates a simplified separation system to reduce cost and increase reliability.[5][10]
Unlike the SRB-A series, which required different burn patterns depending on configuration and vehicle type, the SRB-3 uses a unified burn pattern whether flown in pairs or quartets on the H3, or as the first stage of the Epsilon S.[10]