The H3 rocket is a Japanese medium-lift launch vehicle developed by JAXA and Mitsubishi Heavy Industries (MHI). It is the successor to the H-IIA and H-IIB rockets,designed to reduce launch costs through the use of the lower-cost LE-9 main engine. The H3 features a modular design with two or three first-stage engines and zero,two,or four solid rocket boosters,allowing it to accommodate a variety of payload sizes. Development began in 2013,and the first flight took place in March 2023;the launch ended in failure when the second-stage engine did not ignite. The first successful test flight occurred in February 2024.
The Japanese government authorized development of the H3 on 17 May 2013.[11] The vehicle is being jointly developed by JAXA and MHI to support a wide range of commercial satellite launches. Compared with the H-IIA,the H3 was designed with simpler,lower-cost engines to reduce manufacturing time,technical risk,and overall expense. JAXA and MHI were responsible for preliminary design work,ground facility readiness,new technology development,and manufacturing. Cost reduction was the primary design goal,with launch prices projected at about US$37 million.[12]
As of 2015,the first H3 launch was planned for Japanese fiscal year (JFY) 2020 in the H3-30 configuration,which lacks solid rocket boosters,followed by a booster-equipped version in JFY21.[13][2]
The newly developed LE-9 engine was the key to cost reduction,improved safety,and higher thrust. The engine employs an expander bleed cycle,a combustion method previously used on the upper-stage LE-5 engine,and never before used on a first-stage.[14] While such cycles typically cannot produce high thrust,the LE-9 was designed to reach 1,471kN (331,000lbf),making its development one of the most significant challenges of the program.[15]
Ground tests of the LE-9 began in April 2017,[16] and the first solid rocket booster tests were conducted in August 2018.[17]
On 21 January 2022,the first H3 launch was postponed to JFY22 or later due to technical issues with the LE-9 engine.[18]
The first launch attempt on 17 February 2023 was aborted just before ignition of the SRB-3 boosters,although the main engines had successfully ignited.[19][20][21] The second launch attempt occurred on 7 March 2023 at 01:37:55 UTC. Approximately five minutes and twenty-seven seconds after launch,the second-stage engine failed to ignite. With the rocket unable to reach the required velocity,JAXA issued a self-destruct command 14 minutes and 50 seconds after launch,destroying the ALOS-3 satellite along with the launch vehicle.[22][23][24][25]
On 17 February 2024,JAXA successfully launched the second test rocket,configured as an H3‑22S. During this flight,the second stage reached the intended orbit,marking the first fully successful H3 launch.[26]
Vehicle description
The H3 is a two-stage launch vehicle. The first stage uses two or three LE-9 engines fueled by 225 tonnes (496,000lb)liquid oxygen and liquid hydrogen (hydrolox) propellants. The first-stage can be fitted with zero,two,or four strap-on SRB-3 solid rocket boosters (SRBs) derived from the SRB-A and fueled with polybutadiene. The second stage is powered by an upgraded LE-5B-3 engine and carries 23 tonnes (51,000lb) of hydrolox propellant.[27][3][28]
Variants
H3 configurations are identified by a two-digit number and a letter. The first digit indicates the number of LE-9 engines on the core stage (two or three),while the second digit indicates the number of SRB-3 solid rocket boosters (zero,two,or four). The final letter specifies the payload fairing:short ("S"),long ("L"),or wide ("W"). For example,the H3-24L has two LE-9 engines,four SRBs,and a long fairing,while the H3-30S has three engines,no SRBs,and a short fairing.[29][30]
As of November2018[update],three configurations were planned:H3-30,H3-22,and H3-24.[29]
The H3-32,a proposed variant with three engines and two SRBs,was cancelled in late 2018 after tests showed that the H3-22 offered better-than-expected performance,reducing the need for the more powerful version. JAXA cited commercial precedent,noting that SpaceX's Falcon 9 frequently launched satellites into a low geostationary transfer orbit,leaving the satellites to raise themselves to a geostationary orbit. Since commercial clients appeared willing to accept this trade-off,JAXA concluded that customers would prefer the less expensive H3-22 even if it required additional onboard satellite propellant.[29]
As of July2015[update],the minimum H3-30 configuration is to carry a payload of up to 4,000kg (8,800lb) into Sun-synchronous orbit (SSO) for about ¥5 billion(equivalent to¥5.55 billionorUS$36.65 million in 2024)[31] and the maximum configuration is to carry more than 6,500kg (14,300lb) into geostationary transfer orbit (GTO).[2] The most powerful H3‑24 variant will deliver more than 6,000kg (13,000lb) of payload to lunar transfer orbit (TLI) and 8,800kg (19,400lb) of payload to geostationary transfer orbit (GTO) (∆V=1830m/s).
As of October 2019,MHI was also studying two concepts for potential use in NASA's Lunar Gateway program:an extended second stage,and a heavy-lift version with three liquid-fueled core stages strapped together,similar to the Delta IV Heavy and Falcon Heavy.[32] The proposed H3 Heavy would have a payload capacity of 28,300kg (62,400lb) to low Earth orbit.[33]
Launch services
H3 will have a "dual-launch capability,but MHI is focused more on dedicated launches" in order to prioritize schedule assurance for customers.[34]
As of 2018,MHI is aiming to price the H3 launch service on par with SpaceX's Falcon 9.[34]
The first flight of the H3 launch vehicle. The second-stage engine failed to ignite due to an electrical circuit failure between the vehicle controller and the engine igniter during ignition.[36]
JAXA suspects payload fairing impacted the second stage during separation.[46] An abnormal decrease in second-stage liquid hydrogen tank pressure was observed during first-stage flight, shortly after fairing separation. The initial second-stage burn lasted 27 seconds longer than planned, followed by unexpected engine shutdown one second into the second burn. Payload stranded in low Earth orbit.[47][48][49]
↑Although designated F7 (Flight 7), it was the rocket's sixth flight. F6, the first launch of the H3-30 configuration, was delayed after defects were found during a July 2025 captive firing test.[43]
↑A Japanese Fiscal Year starts in April of the year and ends in March of the next year. For this case, it denotes launch will occur no earlier than 1 April 2021, and no later than 31 March 2022.
↑Shinya Matsuura (2 February 2021). H3ロケットの主エンジン「LE-9」熱効率向上で世界初に挑戦 (in Japanese). Nikkei Business. Archived from the original on 24 January 2022. Retrieved 23 January 2022.
↑"Development of the LE-X Engine"(PDF). Mitsubishi Heavy Industries Technical Review. 48 (4). December 2011. Archived(PDF) from the original on 9 July 2015. Retrieved 8 July 2015.
↑2020年：H3ロケットの目指す姿(PDF) (in Japanese). JAXA. 8 July 2015. Archived(PDF) from the original on 5 March 2016. Retrieved 8 July 2015.
123H3ロケットの開発状況について(PDF) (in Japanese). JAXA. 29 November 2018. Archived(PDF) from the original on 29 November 2018. Retrieved 29 November 2018.
↑衛星フェアリングとは (in Japanese). JAXA. Archived from the original on 25 September 2022. Retrieved 25 September 2022.
↑H3ロケットの開発状況について(PDF). 宇宙開発利用部会 (in Japanese). 10 December 2019. Archived(PDF) from the original on 10 December 2019. Retrieved 10 December 2019.
↑"Ｈ３ロケット試験機１号機打上げ失敗の原因究明に係る調査・安全小委員会 報告書 【概要】"[Summary Report on the Investigation into the Cause of the H3 Rocket Test Vehicle No. 1 Launch Failure](PDF) (Press release) (in Japanese). JAXA. 26 October 2023.
↑"H3ロケット4号機によるXバンド防衛通信衛星「きらめき3号」の打上げ結果"[Launch result of X-band defense communications satellite "Kirameki-3" by H3 rocket No. 4] (Press release) (in Japanese). JAXA. 4 November 2024.
↑"H3ロケット7号機による新型宇宙ステーション補給機1号機（HTV-X1）の 打上げ結果"[Launch result of new unmanned cargo transfer spacecraft HTV-X1 aboard H3 rocket flight 7] (Press release) (in Japanese). JAXA. 26 October 2025.
↑"Michibiki 5". Next Spaceflight. Retrieved 23 December 2025.
↑"H3ロケット8号機の打上げ失敗及び対策本部の設置"[H3 rocket 8th launch failure and establishment of response headquarters] (Press release) (in Japanese). JAXA. 22 December 2025.
↑"宇宙基本計画⼯程表 (令和5年度改訂)"[Basic Plan on Space Policy (2023 Revision)](PDF) (in Japanese). Cabinet Office. 22 December 2023. p.45. Archived(PDF) from the original on 25 December 2023. Retrieved 26 December 2023.
↑Sato, Toshiaki (27 September 2024). H3ロケット30形態試験機の打上げ計画及び超小型衛星相乗りの実施について(PDF). Ministry of Education, Culture, Sports, Science and Technology (in Japanese). Retrieved 28 October 2024.
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