H3 (rocket)

The H3 rocket is a Japanese medium-lift launch vehicle developed by the Japan Aerospace Exploration Agency (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.

H3

Launch of a H3 rocket carrying the QZS-6 satellite on 2 February 2025
Function	Medium-lift launch vehicle
Manufacturer	Mitsubishi Heavy Industries
Country of origin	Japan
Cost per launch	US$50 million for H3‑30S[1]
Size
Height	63 m (207 ft)[2]
Diameter	5.27 m (17.3 ft)[2]
Mass	574,000 kg (1,265,000 lb) for H3‑24L[3]
Stages	2
Capacity
Payload to SSO
Mass	4,000 kg (8,800 lb) for H3‑30[2]
Payload to GTO
Mass	4,000–7,900 kg (8,800–17,400 lb) for H3‑24[2][4]
Associated rockets
Family	H-II family
Based on	H-IIA · H-IIB
Comparable	Angara A5 Ariane 6 Atlas V Falcon 9 GSLV Long March 7 8 12 LVM3 Soyuz-2
Launch history
Status	Active
Launch sites	Tanegashima, LA-Y2
Total launches	6
Success(es)	5
Failure	1
First flight	7 March 2023
Last flight	26 October 2025
Carries passengers or cargo	ALOS-4 HTV-X IGS QZSS
Boosters – SRB-3
No. boosters	0, 2 or 4
Maximum thrust	2,158 kN (485,000 lbf) each[3]
Total thrust	4,316 or 8,632 kN (970,000 or 1,941,000 lbf)
Specific impulse	283.6 s (2.781 km/s)[5]
Burn time	116 seconds[5]
First stage
Powered by	2 or 3 × LE-9
Maximum thrust	2,944 or 4,416 kN (662,000 or 993,000 lbf)[3]
Specific impulse	425 s (4.17 km/s)
Propellant	LOX / LH2
Second stage
Powered by	1 × LE-5B-3[3]
Maximum thrust	137 kN (31,000 lbf)
Specific impulse	448 s (4.39 km/s)
Propellant	LOX / LH2

Development

MHI oversaw development and leads final assembly of the H3 and its liquid-fuel engines. IHI Corporation produces the liquid-fuel engine turbopumps and solid-fuel boosters, Kawasaki Heavy Industries builds the S and L-type payload fairings, and Toray Industries supplies the carbon fiber and synthetic resin used in the booster motor cases and fairings.^[6][7][8] Beyond Gravity manufactures the W-type fairing based on its standard 5.4-metre-wide (18 ft) design.^[9]

The Japanese government authorized development of the H3 on 17 May 2013.^[10] 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.^[11]

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.^[12][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.^[13] While such cycles typically cannot produce high thrust, the LE-9 was designed to reach 1,471 kN (331,000 lb_f), making its development one of the most significant challenges of the program.^[14]

Ground tests of the LE-9 began in April 2017,^[15] and the first solid rocket booster tests were conducted in August 2018.^[16]

On 21 January 2022, the first H3 launch was postponed to JFY22 or later due to technical issues with the LE-9 engine.^[17]

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.^[18][19][20] 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.^{[21][22][23][24]}

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.^[25]

Vehicle description

The H3 is a two-stage launch vehicle. The first stage uses two or three LE-9 engines fueled by 225 tonnes (496,000 lb) 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 (51,000 lb) of hydrolox propellant.^[26][3][27]

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.^[28][29]

As of November 2018^[update], three configurations were planned: H3-30, H3-22, and H3-24.^[28]

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.^[28]

As of July 2015^[update], the minimum H3-30 configuration is to carry a payload of up to 4,000 kg (8,800 lb) into Sun-synchronous orbit (SSO) for about ¥5 billion (equivalent to ¥5.1 billion or US$46.76 million in 2019)^[30] and the maximum configuration is to carry more than 6,500 kg (14,300 lb) into geostationary transfer orbit (GTO).^[2] The most powerful H3‑24 variant will deliver more than 6,000 kg (13,000 lb) of payload to lunar transfer orbit (TLI) and 8,800 kg (19,400 lb) of payload to geostationary transfer orbit (GTO) (∆V=1830 m/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.^[31] The proposed H3 Heavy would have a payload capacity of 28,300 kg (62,400 lb) to low Earth orbit.^[32]

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.^[33]

As of 2018, MHI is aiming to price the H3 launch service on par with SpaceX's Falcon 9.^[33]

Launch history

See also: List of H-II series and H3 launches § 2024

Past launches

Sources: Japanese Cabinet^[34]

Flight No.	Date and time (UTC)	Version	Launch site	Payload(s) and notes	Launch outcome
TF1	7 March 2023, 01:37:55	H3‑22S[35]	Tanegashima, LA‑Y2	ALOS-3 (Daichi-3)	Failure Second stage engine did not ignite.[36]
TF2	17 February 2024, 00:22:55	H3‑22S	Tanegashima, LA‑Y2	Vehicle Evaluation Payload (with rideshares: CE-SAT-1E / TIRSAT)[37]	Success[38]
F3	1 July 2024, 03:06:42	H3‑22S	Tanegashima, LA‑Y2	ALOS-4 (Daichi-4)	Success[39]
F4	4 November 2024, 06:48:00	H3‑22S	Tanegashima, LA‑Y2	DSN-3 (Kirameki 3)	Success[40][41]
F5	2 February 2025, 08:30:00	H3‑22S	Tanegashima, LA‑Y2	QZS-6 (Michibiki-6)	Success[42]
F7[a]	26 October 2025, 00:00:15	H3-24W[44]	Tanegashima, LA‑Y2	HTV-X1 - In-flight demonstration of AFSS and TDRS telemetry[44]	Success[45]

1. 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]

Future launches

Date and time (UTC)	Version	Payload(s)
7 December 2025	H3-22S	QZS-5 (Michibiki-5)
JFY25[46]	H3-30S	Vehicle Evaluation Payload (with rideshares: PETREL / STARS-X / VERTECS / HORN L / HORN R / BRO-19)
JFY25	H3-22S	QZS-7 (Michibiki-7)
JFY25	H3-24L	ETS-IX
JFY26	H3‑24W	HTV-X2
JFY26	H3-24L	MMX
JFY26	H3-24W	HTV-X3
JFY26	H3	IGS-Optical Diversification 1
2026–28	H3	LUPEX
JFY27	H3	IGS-Optical 9
JFY27	H3	IGS-Optical Diversification 2
2027	H3	JDRS-2
2027	H3	ALOS-3 successor
2027	H3	Eutelsat (TBD)[47]
March 2028	H3	MBR Explorer
JFY28	H3	Himawari 10
2028[48]	H3	DESTINY+
2028	H3	ALOS-4 successor
JFY29	H3	IGS-Radar Diversification 1
JFY29	H3	IGS-Optical 10
JFY30	H3	IGS-Radar Diversification 2
JFY31	H3	IGS-Radar 9
JFY32	H3	IGS-Optical Diversification Successor
JFY32	H3	LiteBIRD
JFY33	H3	IGS-Radar 10
JFY33	H3	IGS-Optical 11
TBD	H3	Inmarsat (satellite TBD)[49]

Notes