JAXA Completes Epsilon S Engine Firing Test for FY2026 Launch

01The Story新闻事实

JAXA completed a two-minute ground firing test of the Epsilon S rocket second-stage engine on July 23, 2026. After two explosion accidents, JAXA reverted to a conventional engine design to ensure a FY2026 launch restart.2026年7月23日，JAXA完成Epsilon S火箭第二级发动机2分钟地面燃烧测试。经历两次爆炸事故后，JAXA改用传统发动机方案，以争取在2026财年内恢复发射。

JAXA completed a 2-minute ground static firing test of the Epsilon S second-stage engine on July 23, 2026.JAXA于2026年7月23日完成Epsilon S第二级发动机约2分钟地��静止燃烧测试。
Following explosions in July 2023 and November 2024, JAXA reverted to a conventional Epsilon engine design.经历2023年7月与2024年11月两次爆炸后，JAXA退回使用传统Epsilon发动机设计。
JAXA plans to launch Epsilon S Flight 7 in FY2026 carrying Vietnam's LOTUSat-1 satellite.JAXA计划于2026财年发射Epsilon S 7号试验机，运载越南LOTUSat-1卫星。

Reverting to a conventional engine enables JAXA to restart launches in FY2026, but reduced payload capacity threatens Japan's commercial launch competitiveness.改用传统发动机保障了JAXA在2026财年复飞，但运力下降削弱了日本在商��发射市场的竞争力。

024 Dimensions维度分析

Historical context历史脉络

Development Delays and Explosion Accidents研��历程与两次爆炸��故

Two motor explosion accidents in 2023 and 2024 delayed Epsilon S development by three years, forcing JAXA to alter engine specifications.2023与2024年两次发动机爆炸事故导致Epsilon S研制延误3年，迫使JAXA修改发动机规格。

July 2023 – July 20262023年7月—2026年7月 3 years3年
July 23, 2026 test2026年7月23日测试 130 seconds130秒

On July 14, 2023, the Epsilon S second-stage motor exploded 57 seconds into a test at Noshiro due to thermal insulator failure.2023年7月14日，Epsilon S第二级发动机在能代实验场测试第57秒发生爆燃。
On November 26, 2024, a revised second-stage motor exploded 49 seconds after ignition at Tanegashima Space Center.2024年11月26日，改良型第二级发动机在种子岛宇宙中心点火49秒后再次爆炸。
In October 2022, Epsilon Flight 6 failed mid-flight due to a reaction control system diaphragm rupture.2022年10月，Epsilon 6号机因姿态控制系统部件故障导致飞行失败并自毁。

Comparison对比

Launch Readiness Speed vs Payload Capacity恢复发射速度与运载能力折衷

Reverting to the conventional M-35a motor restores launch schedule stability but sacrifices high-altitude payload performance.退回使用M-35a传统发动机保障了发射日程，但牺牲了高轨道运载能力。

Target SSO payload capacity (Original design)SSO轨道目标运载能力（原设计）

Original specification原设计指标600 kg

2026 specification2026年规格99,000 kg

Epsilon S was designed to carry over 600 kg to Sun-Synchronous Orbit using a new high-propellant second stage.Epsilon S原计划采用新型第二级发动机，实现太阳同步轨道600公斤以上运力。
Using the conventional M-35a engine design reduces payload weight, increasing cost-per-kilogram for satellite customers.采用传统M-35a发动机导致运力下降，抬高了单位公斤发射成本及客户费用。

Stakeholder impact利益相关方

International Satellite Launch Commitments国际卫星发射履约与客户影响

Successful motor qualification allows Japan to fulfill its delayed launch contract for Vietnam's LOTUSat-1 satellite.发动机测试通过使日本得以履约，为越南发射延迟已久的LOTUSat-1雷达观测卫星。

Vietnam's LOTUSat-1 synthetic aperture radar satellite weighs 580 kg and is manufactured by Japan's NEC Corporation.越南LOTUSat-1合成孔径雷达卫星重580公斤，由日本电气公司（NEC）承造。
Repeated rocket test failures delayed LOTUSat-1's launch from its original 2023 schedule into FY2026.火箭测试屡次失利导致LOTUSat-1发射日程从原定2023年推迟至2026财年。

Consequence影响推演

Solid-Fuel Strategic Value for Defense固体燃料技术与国家安全即时响应

Unlike liquid-fueled rockets, solid-propellant Epsilon S can be stored pre-fueled for rapid defense emergency deployment.与液体火箭不同，固体燃料Epsilon S可预加注长期储存，具备国防危机的即时发射能力。

Professor Atsushi Osanai notes solid-fuel rockets allow long-term pre-fueled storage for rapid replacement of destroyed defense satellites.长内厚教授指出固体火箭支持长期加注备战，可在卫星遭破坏时快速发射替代卫星。

— Nikkei

Epsilon S employs solid propellant across all three main stages, streamlining ground launch procedures compared to H3.Epsilon S全三级主推进均采用固体燃料，发射准备流程较液体火箭H3显著简化。

03Timeline时间线

2013-09-14 JAXA launches first-generation Epsilon rocket Flight 1.JAXA成功发射第一代Epsilon火箭首飞机。
2022-10-12 Epsilon Flight 6 fails after launch and self-destructs.Epsilon 6号机发射失败并执行空中自毁。
2023-07-14 Epsilon S 2nd-stage motor explodes during test at Noshiro.Epsilon S第二级发动机在能代实验场爆燃。
2024-11-26 Redesigned Epsilon S 2nd-stage motor explodes at Tanegashima.改进型Epsilon S第二级发动机在种子岛爆炸。
2026-07-23 Epsilon S conventional M-35a engine test succeeds at Tanegashima.Epsilon S传统M-35a发动机在种子岛完成燃烧测试。
2027-03-31 Target deadline for Epsilon S Unit 7 Maiden Flight in FY2026.Epsilon S 7号试验机2026财年内首飞目标期限。

Key takeaway核心结论

Engine test success enables a FY2026 launch restart, but dual-track development is required to restore full market competitiveness.发动机测试成功奠定2026财年复飞基础，但日本仍需双轨研发以恢复商业竞争力。

04What to Watch后续关注

JAXA's detailed telemetry analysis of the July 23 engine test.JAXA对7月23日发动机燃烧测试数据的详细解析结果。
Final integration timeline for Epsilon S Unit 7 carrying LOTUSat-1.Epsilon S 7号试验机与LOTUSat-1卫星的总装整合日程。
R&D progress on the next-generation high-thrust modified engine.新一代高推力改良型发动机的平行研发推进进度。

05Uncertainties不确定因素

Payload capacity penalty of the M-35a engine on commercial launch pricing.改用传统M-35a发动机导致的运力折损对商业定价的影响。
Readiness of international satellite payloads before the FY2026 launch window.国际搭载卫星在2026财年发射窗口前的交付备战状态。

06Sources信息来源

Epsilon S Rocket Engine Test Completed, Targeted for Launch in FY2026Epsilon S火箭发动机测试完成拟于2026财年内发射 Nikkei · 2026-07-23
Ground Firing Test Results of the Epsilon S Second-Stage Motor (M-35a)Epsilon S第二级发动机（M-35a）地面燃烧测试结果 Japan Aerospace Exploration Agency (JAXA) · 2026-07-23
Epsilon S Launch Vehicle Specifications and CapabilitiesEpsilon S运载火箭规格与性能指标 IHI Aerospace · 2024-03-15
LOTUSat-1 Earth Observation Satellite Development and Launch ScheduleLOTUSat-1地球观测卫星研制与发射计划 Vietnam National Space Center (VNSC) · 2025-01-10
Chronology of Epsilon and Epsilon S Firing Test FailuresEpsilon及Epsilon S火箭燃烧测试与发射失败记录 Yomiuri Shimbun · 2024-11-27

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