LE-5B
LE-5B is the expander-bleed cryogenic upper-stage engine developed from LE-5A for H-IIA. Its chamber-cooling heat supplies turbine-driving hydrogen, and it supports repeated ignition in orbit. JAXA lists 137 kN vacuum thrust, 448 s vacuum specific impulse, 2.8 m overall length and 290 kg mass. LE-5B-2 later revised the mixer and injector to reduce combustion-pressure fluctuations and vehicle vibration.
Identity
- Domains
- spaceflight
- Identity Level
- variant
- Kind
- liquid-rocket-engine
- Name
- LE-5B
- Status
- retired
Details
- Description
- LE-5B is the expander-bleed cryogenic upper-stage engine developed from LE-5A for H-IIA. Its chamber-cooling heat supplies turbine-driving hydrogen, and it supports repeated ignition in orbit. JAXA lists 137 kN vacuum thrust, 448 s vacuum specific impulse, 2.8 m overall length and 290 kg mass. LE-5B-2 later revised the mixer and injector to reduce combustion-pressure fluctuations and vehicle vibration.
- Dry Mass
- …
- Family
- Length
- …
- Lineage
- Note
- JAXA explicitly describes LE-5B as an improved LE-5A.
- Related Propulsion System
- Relationship
- direct-derivative-of
- Sources
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B
- Propellants
- liquid hydrogenliquid oxygen
- Rocket Specs
- Cycle
- expander-bleed
- Restartable
- Yes
- Vacuum Specific Impulse
- …
- Vacuum Thrust
- …
Links
Assets & Meta
- Creation Time
- July 29, 2026 at 08:48:39 UTC
- Updated Time
- October 29, 2026 at 15:30:54 UTC
Other
- Sources
- Accessed Date
- 2026-07-29
- Note
- Supports the legacy vehicle installation and the narrow canonical identity used for migration.
- Publisher
- Official vehicle or program source
- Title
- H-IIA Launch Vehicle official vehicle reference
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- July 2025 President's Press Conference: H-IIA Flight 50
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B
- Accessed Date
- 2026-10-29
- Note
- LE-5B table: 137 kN vacuum thrust, 448 s vacuum Isp, 2.8 m length, 290 kg mass; chamber-expander-bleed cycle and multiple ignition.
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B and LE-5-series engine comparison