H3

Launch of a H3 rocket carrying theQZS-6 satellite on2 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 toSSO
Mass	4,000 kg (8,800 lb) for H3‑30[2]
Payload toGTO
Mass	4,000–7,900 kg (8,800–17,400 lb) for H3‑24[2][4] ≥6,500 kg (14,300 lb) (ΔV=1500 m/s)[5]
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)[6]
Burn time	~110 seconds[6]
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)
Burn time	292 seconds[citation needed]
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
[edit on Wikidata]

TheH3 rocket is a Japanesemedium-lift launch vehicle developed byJAXA andMitsubishi Heavy Industries (MHI). It is the successor to theH-IIA andH-IIB rockets, designed to reduce launch costs through the use of the lower-costLE-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.

MHI oversaw development and leads final assembly of the H3 and its liquid-fuel engines.IHI Corporation produces the liquid-fuel engineturbopumps and solid-fuel boosters,Kawasaki Heavy Industries builds the S and L-typepayload fairings, andToray Industries supplies thecarbon fiber andsynthetic resin used in the booster motor cases and fairings.^[7][8][9]Beyond Gravity manufactures the W-type fairing based on its standard 5.4-metre-wide (18 ft) design.^[10]

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 theH-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 forJapanese 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 developedLE-9 engine was the key to cost reduction, improved safety, and higher thrust. The engine employs anexpander bleed cycle, a combustion method previously used on the upper-stageLE-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 1,471 kN (331,000 lb_f), 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 01:37:55UTC. 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 theALOS-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]

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 andliquid hydrogen (hydrolox) propellants. The first-stage can be fitted with zero, two, or four strap-on SRB-3solid rocket boosters (SRBs) derived from theSRB-A and fueled withpolybutadiene. The second stage is powered by an upgraded LE-5B-3 engine and carries 23 tonnes (51,000 lb) of hydrolox propellant.^[27][3][28]

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 November 2018^[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 lowgeostationary transfer orbit, leaving the satellites to raise themselves to ageostationary 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 July 2015^[update], the minimum H3-30 configuration is to carry a payload of up to 4,000 kg (8,800 lb) intoSun-synchronous orbit (SSO) for about¥5 billion (equivalent to¥5.1 billion or US$46.76 million in 2019)^[31] and the maximum configuration is to carry more than 6,500 kg (14,300 lb) intogeostationary transfer orbit (GTO).^[2] The most powerful H3‑24 variant will deliver more than 6,000 kg (13,000 lb) of payload tolunar transfer orbit (TLI) and 8,800 kg (19,400 lb) of payload togeostationary 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 theDelta IV Heavy andFalcon Heavy.^[32] The proposed H3 Heavy would have a payload capacity of 28,300 kg (62,400 lb) to low Earth orbit.^[33]

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 H3launch service on par with SpaceX's Falcon 9.^[34]

Sources:Japanese Cabinet^[35]

Wikimedia Commons has media related toH3 (rocket).

• JAXA H3 English page
• JAXA H3 pamphlet
• JAXA TODAY No. 10

• Mitsubishi Heavy Industries space launch vehicles
• Expendable space launch systems

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