Japan’s H3 rocket awaiting final engine certification for first flight

by Lee Kanayama

Japan’s third-generation liquid hydrogen-powered rocket, H3, is nearing closer to its first launch. The H3 rocket is co-developed by the Japan Aerospace Exploration Agency (JAXA) and Mitsubishi Heavy Industries (MHI), succeeding the H-II family, which provided satellite launches and International Space Station cargo resupply missions for two decades.

The H3 rocket is the third in Japan’s hydrogen-powered rocket family. The first was the H-I rocket used from 1986 to 1992. Then, the vehicle used an American-built Extended Long Tank Thor (ELTT) with either six or nine Caster-2 solid rocket boosters (SRBs).

This was the first Japanese rocket to use a Japanese-built cryogenic second stage using their new LE-5 engine. The H-I was 2.44 meters in diameter and had a height of 42 meters. The H-I successfully flew nine times with a 100% success record.

The H-I was replaced in 1994 by the H-II, the first all Japanese-built liquid rocket. The ELTT first stage was replaced by a Japanese-built first stage now powered by a single LE-7 hydrolox engine.  H-II also included a single upgraded LE-5A hydrolox second-stage engine and twin Japanese-built solid rocket boosters.

The rocket was 4 meters in diameter with a height of 49 meters. It flew seven times from 1994 to 1999 with five successful launches. The H-II was then retired in favor of the H-IIA and H-IIB rockets.

H-IIA is Japan’s main launch system currently in operation. It uses a single LE-7A first-stage hydrolox engine, a single LE-5B second-stage hydrolox engine, and two or four SRB-A solid rocket boosters. H-IIA is the same 4-meter diameter as H-II but taller at 53 meters. H-IIA took its maiden flight in 2001 and currently sits at 43 launches with 42 successes. 

Launch of the H-IIA Flight 40 with IBUKI-2 (GOSAT-2) and KhalifaSat – via JAXA

H-IIB was a more powerful version of H-IIA to support the now-retired Kounotori H-II Transfer Vehicle (HTV). The rocket used two LE-7A engines on the first stage and the same second stage as the H-IIA. H-IIB was larger than H-IIA at 5.2 meters in diameter at 56.6 meters tall. It launched nine ISS resupply missions from 2009 to 2020 with a 100% success record.

The H3 program started in 2014 to replace the aging H-II family to lower the overall cost per launch. More similar to the H-IIB than the H-IIA, H3 is a two-stage expendable launch system with three main configurations. H3 will be 5.2 meters in diameter with an approximate height of 63 meters, making H3 the largest rocket Japan has ever built.

The H3 will have a starting price of $45 million (about 5 billion Japanese Yen) per launch, making it about half the price of the H-IIA.

The first stage of the H3 will use two or three LE-9 hydrolox rocket engines, the newest rocket engine Japan has developed for a space launch vehicle. Derived from the LE-5 rocket engine, the LE-9 will generate 1472 kN of thrust with a specific impulse of 425 seconds. In addition, the engine will use an expander bleed cycle, similar to the American BE-3U rocket engine developed by Blue Origin.

The first LE-9 engine was assembled and installed at the Tanehashima Space Center rocket engine test stand in March 2017. Designed by JAXA, the engine is manufactured by Mitsubishi Heavy Industries (MHI).

The first engine, model 1-1, successfully completed 11 of its 11 planned engine tests from April 2017 to July 2017. Most tests successfully completed full-duration burns lasting from two to 78 seconds. However, engine tests three, eight, and nine all ended early due to issues with turbopump rotation speeds.

From 2017 to 2019, four more development LE-9 engines were also successfully tested.

In early 2020, MHI and JAXA started testing the first certification engine for use on the H3 rocket. During its eighth of 14 planned tests, an issue was found with the combustion chamber wall and the LH2 turbopump. The combustion wall and turbopump were found to have fatigue fractures.

These issues were fixed but have caused the first launch to be delayed from late 2020 to 2021. In 2021, the LE-9 engine has continued to undergo certification tests, with the second certified engine currently on its third of ten tests. 

The H3 test tank and LE-9 engines going through the “Battleship” test – via JAXA

The LE-9 engine completed several important milestones in 2019 and 2020 with the “Battleship” firing tests. The first test was completed in January 2019, using two engines on a first stage test tank. In 2020, a three-engine “Battleship” test was conducted, also using a first-stage test tank. These tests gave MHI and JAXA data to see how the engines will react to the stresses of multiple engines firing at once.

Either two or three LE-9 engines will power the first stage of the H3 rocket. Two engines will be used on the first stage if any SRBs are used for the launch, while three engines will be used if no SRBs are to be flown.  The first stage will generate 2,942 kN or 4,413 kN of thrust, depending on how many engines are used for the flight.

The SRB to be used on the H3 rocket is the SRB-3. The SRB-3 design is derived from the SRB-A, which is used on the H-IIA and Epsilon rockets. SRB-3 will be slightly shorter than its predecessor but has more solid propellant and generates more thrust at 2,158 kN. Zero, two, or four of these boosters can be used on the H3 rocket first stage. 

The first completed SRB-3 underwent its static fire test in August 2018. Two more tests took place in 2019 and 2020 to certify SRB-3 for H3. In addition, a full-scale separation test was also completed in 2019.

The first stage and optional SRBs will accelerate the second stage, payload fairing, and payload(s) to space. The second stage, powered by a single LE-5B-3 hydrolox engine, will place itself and the payload(s) into the intended orbit.

The LE-5B-3 is the latest version of the LE-5 engine. The new variant is designed to improve performance while reducing the cost of the engine. LE-5B-3 will generate 137 kN of thrust with a specific impulse of approximately 448 seconds. It will be using an expander bleed cycle just like the LE-9 engine.

Evolution of Japanese hydrolox engines – via JAXA

The LE-5B-3 first conducted its own certification test in 2017 and has successfully undergone 20 engine firings. A second engine was tested throughout 2018 and 2019 to complete the certification of the engine.

The second stage will also have the payload fairing on top of it to protect its payload(s). The fairing will have two short and long variants, but both will be 5.2 meters in diameter. In December 2019, a fairing separation test was successfully completed.

All of these successful tests culminated in the assembly of the H3 Test Flight No. 1 (TF1) launch vehicle. In 2020, the engines were installed on the first and second stages of the TF1. This allowed the rocket to undergo functional tests while at the Tobishima Plant in the Aichi Prefecture.

In January 2021, testing was completed, and the rocket was shipped to the Tanegashima Space Center. A month later, the rocket, along with two SRB-3s, was placed on Movable Launcher 5 (ML-5) in the H-IIB Vehicle Assembly Building (VAB). The operation, known as Vehicle On Stand (VOS), was the last important milestone before the rocket would conduct a Wet Dress Rehearsal (WDR). A mockup payload fairing was placed on top of the second stage. 

In March 2021, the H3 rocket was rolled out to the Yoshinobu Launch Complex (LC-Y) Pad 2. After arriving at Pad 2, the rocket was loaded with Liquid Oxygen and Liquid Hydrogen for the WDR.

A Wet Dress Rehearsal, or WDR, is where a rocket is fueled in order to test the rocket, countdown procedures, and grounds systems before a launch. The rocket went into the launch countdown until T-8 seconds, when the clock was stopped as planned. The test was completed, and the fuel was unloaded. Shortly thereafter, the rocket was rolled back to the VAB. Inspections were completed, and the vehicle was confirmed to be in healthy condition.

H3 on LC-Y Pad 2 ready for the WDR – via JAXA

Since then, H3 has been waiting in the VAB for future testing and final certification of the LE-9 engine. TF1 is scheduled to launch in Q1 2022 with the Advanced Land Observation Satellite 3 (ALOS-3).

TF1 will launch in an H3-22S configuration. The first digit of the configuration shows how many LE-9 engines are on the first stage, which can either be a two or three. The second digit shows how many SRB-3s will support the mission. And the final letter states which fairing is being used.

For ALOS-3, it will launch with two LE-9 engines, two SRB-3s, and the short payload fairing. H3 will take ALOS-3 to a 669-kilometer orbit at 97.8 degrees inclination, a Sun-Synchronous Orbit.

With these rocket configurations, H3 will be able to lift up to 3 tons to a Sun-Synchronous Orbit or 6.5 tons to a 1.5 km/s Geostationary transfer orbit (GTO), meaning a transfer orbit where 1.5 km/s of Delta-V is required to reach the operational Geostationary orbit.

Once H3 becomes operational, the H-IIA will be retired in 2023. H3 will later support commercial communication satellites, science, and exploration missions, including the HTV-X ISS cargo resupply ship.

The HTV-X (Kotonotori) is JAXA’s next-generation cargo resupply ship for the ISS. The Kotonotori is designed to lower the vehicle’s overall mass while allowing more unpressurized cargo to the ISS. It will be able to be berthed to the ISS for up to six months and free fly in orbit for up to 18 months. It is scheduled to launch for the first time in late 2022 on an H3-24L.

Both H3 and Kotontori will also have a possibility of supporting NASA’s Gateway Lunar space station. A future variant of the H3 will be a tri-core H3 Heavy rocket to carry the HTV-XG variant to lunar orbit. HTV-XG will also possibly launch on other smaller H3 variants or American launch vehicles like Falcon Heavy. An HTV-XG could launch as early as 2025 and H3 Heavy as early as 2030.

(Lead render of the H3 rocket in flight – via Mack Crawford for NSF/L2)

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