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.
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 (8ft 2in) in diameter and 15.1 metres (50ft) 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
Closeup of SRB-3 models attached to a model H3 rocket
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 (2,200lb) 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]
1 2 "H3プロジェクト前進へ"(PDF). 宇宙航空の最新情報マガジン JAXA's. 74. JAXA: 10. 1 October 2018. Archived from the original(PDF) on 18 March 2022. Retrieved 17 February 2023.
* Different versions of the engine use different propellant combinations
Engines in italics are/were under development
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
