LE-5B-3
LE-5B-3 is H3’s restartable liquid-hydrogen/liquid-oxygen second-stage engine, developed from LE-5B-2. Mixer and hydrogen-turbine changes improve efficiency and operating life. JAXA lists 137 kN vacuum thrust, 448 s vacuum specific impulse, approximately 300 kg mass, 2.8 m length and 1.690 m maximum diameter. Its published operating envelope includes 740 seconds at full thrust, 250 seconds in idle mode and three ignitions; these are engine capabilities rather than one mandatory mission sequence.
Identity
- Domains
- spaceflight
- Identity Level
- variant
- Kind
- liquid-rocket-engine
- Name
- LE-5B-3
- Status
- active
Details
- Description
- LE-5B-3 is H3’s restartable liquid-hydrogen/liquid-oxygen second-stage engine, developed from LE-5B-2. Mixer and hydrogen-turbine changes improve efficiency and operating life. JAXA lists 137 kN vacuum thrust, 448 s vacuum specific impulse, approximately 300 kg mass, 2.8 m length and 1.690 m maximum diameter. Its published operating envelope includes 740 seconds at full thrust, 250 seconds in idle mode and three ignitions; these are engine capabilities rather than one mandatory mission sequence.
- Dry Mass
- …
- Family
- Length
- …
- Lineage
- Note
- JAXA documents LE-5B-3 as an H3-focused design evolution of LE-5B-2.
- Related Propulsion System
- Relationship
- direct-derivative-of
- Sources
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B-3
- Propellants
- liquid hydrogenliquid oxygen
- Rocket Specs
- Cycle
- expander-bleed
- Restartable
- Yes
- Vacuum Specific Impulse
- …
- Vacuum Thrust
- …
Links
- Official Url
- https://www.rocket.jaxa.jp/rocket/h3/le5b.html
Assets & Meta
- Creation Time
- July 29, 2026 at 08:49:17 UTC
- Updated Time
- October 29, 2026 at 15:30:57 UTC
Other
- Diameter
- …
- 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
- H3-30S official vehicle reference
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- H3 Launch Vehicle: LE-5B-3 and LE-9
- Accessed Date
- 2026-07-29
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B-3
- Accessed Date
- 2026-10-29
- Note
- Exact-model table: 137 kN vacuum thrust, 448 s vacuum Isp, approximately 300 kg mass and 2.8 m length; 1690 mm maximum diameter, 740 s full-thrust and 250 s idle operation, three ignitions.
- Publisher
- Japan Aerospace Exploration Agency
- Title
- LE-5B-3