LE-5B-2
LE-5B-2 is the vibration-reduced development of the LE-5B liquid-hydrogen/liquid-oxygen expander-bleed engine. JAXA revised its hydrogen mixer and injector after large low-frequency oscillations on H-IIA Flight 3, reducing combustion-pressure fluctuations and vibration. LE-5B-2 was installed from H-IIA Flight 14 onward and on H-IIB. Further developments added idle-mode operation for controlled stage disposal and throttling for insertion accuracy. JAXA compares its 446.6 s specific impulse with the later LE-5B-3 design’s 448.0 s; these are distinct upper-stage engine developments.
Identity
- Domains
- spaceflight
- Identity Level
- variant
- Kind
- liquid-rocket-engine
- Name
- LE-5B-2
- Status
- retired
Details
- Description
- LE-5B-2 is the vibration-reduced development of the LE-5B liquid-hydrogen/liquid-oxygen expander-bleed engine. JAXA revised its hydrogen mixer and injector after large low-frequency oscillations on H-IIA Flight 3, reducing combustion-pressure fluctuations and vibration. LE-5B-2 was installed from H-IIA Flight 14 onward and on H-IIB. Further developments added idle-mode operation for controlled stage disposal and throttling for insertion accuracy. JAXA compares its 446.6 s specific impulse with the later LE-5B-3 design’s 448.0 s; these are distinct upper-stage engine developments.
- Family
- Lineage
- Note
- JAXA documents LE-5B-2 as a design update of LE-5B to reduce combustion-pressure oscillation.
- 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 08:48:42 UTC
- Updated Time
- October 29, 2026 at 15:36:34 UTC
Other
- Sources
- Accessed Date
- 2026-07-29
- Note
- Supports the canonical H-IIB upper-stage installation.
- Publisher
- Japan Aerospace Exploration Agency
- Title
- H-IIB Launch Vehicle
- Accessed Date
- 2026-08-15
- Note
- JAXA identifies the currently operated LE-5B-2 as a LE-5B update with multiple ignition, idle-mode low-thrust controlled-reentry, and throttling functions for higher orbital-insertion accuracy.
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B
- 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
- Explains mixer/injector revisions, adoption from H-IIA Flight 14 and on H-IIB, idle and throttle functions, and 446.6 s Isp in comparison with LE-5B-3.
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B engine: design improvements