Japan’s H3 rocket made a second attempt to reach orbit on Saturday, 11 months after it failed during its maiden flight. The rocket successfully sent a mass simulator and two small satellites to the same 669-kilometer Sun-synchronous orbit it targeted on the previous mission. Liftoff commenced at 00:22 UTC (9:22 AM local time) from Launch Pad 2 of the Yoshinobu Launch Complex of the Tanegashima Space Center.
The Japan Aerospace Exploration Agency (JAXA) and Mitsubishi Heavy Industries (MHI) developed the H3 as a successor to the previous-generation H-IIA and H-IIB vehicles. The H-IIA, which first flew in 2001, has been a workhorse of Japan’s space program, but only has two launches remaining and is expected to retire by the end of the year. The more powerful H-IIB made its final flight in 2020.
H3 made its first flight on March 7, 2023, with the Advanced Land Observing Satellite 3 (ALOS-3) satellite aboard. The mission proceeded nominally through first stage flight and stage separation as planned. However, the rocket’s second stage failed to ignite. Thirteen minutes and 55 seconds after liftoff, once it had become clear that the rocket would not be able to reach orbit, the flight termination system (FTS) was commanded to destroy the vehicle.
An investigation determined three possible causes of the failure, focusing on an abnormal power reading detected at the moment the second stage ignition command was sent. The scenarios identified were a short-circuit of the igniter, an overcurrent in the igniter, or an overcurrent in the second stage’s primary propulsion system controller which spread to the redundant controller. Changes were proposed to ensure these failure modes could not occur on future missions and have been implemented ahead of H3’s return to flight with Saturday’s mission.
Saturday’s launch is designated Test Flight 2, or TF2. With H3’s maiden flight having been unsuccessful, the primary payload for TF2 was Vehicle Evaluation Payload 4 (VEP–4). VEP–4 is a mass simulator that mimics the presence of a spacecraft aboard the rocket without risking the cost and project impact of losing another large satellite in the case of TF2 not succeeding in its mission.
To give the best possible indication that issues experienced during the first test flight have been resolved, TF2 followed a similar launch profile to TF1, and VEP–4 was built with the same mass as ALOS–3 — around 3,000 kilograms. VEP–4 follows on from three previous VEPs – carried aboard the first H-II launch in 1994, and the first and second H-IIA launches in 2001 and 2002 – which were instrumented to gather data about the performance and operation of their launch vehicles.
In addition to VEP–4, Saturday’s launch also carried a pair of small satellites — CE-SAT–1E and TIRSAT — as secondary payloads. These are lower-cost, less risk-averse missions taking advantage of excess payload capacity aboard H3 to get a ride into orbit. CE-SAT–1E, or Canon Electric Satellite 1E, is part of a series of lightweight imaging satellites being developed by Canon Electronics, incorporating imagers based on Canon’s range of commercially available cameras. Its primary instrument is based around a Canon EOS R5 camera, with a 40-centimeter reflector telescope, while a secondary imager has been derived from a PowerShot S110 camera.
TIRSAT is a three-unit CubeSat with a mass of about six kilograms. A partnership between Japan Space Systems, Seiren Corporation, and several other organizations and universities, the satellite will perform on-orbit validation of the Uncooled Small Infrared Sensor, a thermal infrared imaging payload intended for future missions. Infrared imaging allows heat emissions to be identified and observed; potential applications include industrial monitoring and disaster management.
The two secondary payloads are mounted on either side of VEP–4 and separated into low-Earth orbit (LEO) during a coast phase after the end of the second stage’s first engine burn. CE-SAT–1E was deployed using a SimplePAF15M payload attachment fitting (PAF), while TIRSAT is housed within a standard CubeSat dispenser.
H3 is a two-stage rocket, with both stages burning cryogenic liquid hydrogen and liquid oxygen propellants. It can fly in several different configurations, varying the number of first-stage engines, the number of solid rocket boosters augmenting the first stage, and the length of the payload fairing. Each configuration has a three-character designation, with the first digit indicating the number of engines on the first stage, the second indicating the number of solid boosters, and the third character being either an “S” or “L” to denote the use of a short or long fairing, respectively.
In all configurations, the first stage is powered by LE–9 engines, with the second stage using a single LE–5B–3. In configurations that use solid rocket motors, IHI Aerospace’s SRB–3 boosters (not to be confused with the SRB-A3 used on H-IIA) are attached radially around the base of the first stage to provide additional thrust.
The three-engine version of H3’s first stage will be used without boosters in the 30S and 30L configurations. The 22S and 22L configurations have twin-engine first stages with two solid rocket motors, and the 24S and 24L use the same first stage with four boosters. The short payload fairing is 10.4 meters long, while the long fairing measures 16.4 meters in length. Both types of fairing have the same diameter: 5.2 meters.
The TF2 mission used an H3–22S, the same configuration that flew the maiden flight. Its launch took place from Launch Pad 2 (LP2) of the Yoshinobu Launch Complex, part of JAXA’s Tanegashima Space Center located on the island of Tanegashima, off the south coast of Kyushu.
LP2 was built in the early 2000s as a backup pad for H-IIA launches, however, it has never been used by the H-IIA. Instead, its first launch came in 2009 with the debut of the H-IIB rocket, which made all nine of its launches from LP2. H3’s maiden flight was also made from LP2 last year. The nearby Launch Pad 1 is older, having been constructed ahead of the H-II’s first launch in 1994, and continues to be used by the H-IIA.
Despite being in the same configuration, the rocket flying the TF2 mission differs slightly from the one that flew TF1. Changes to the second-stage engine igniter and propulsion system controllers have been made based on the findings of the investigation into TF1’s failure, while one of the first-stage engines was the LE–9 Type 1A which includes upgrades over the standard LE–9 Type 1 to improve its reliability.
First stage of the H3 TF2 rocket is raised to vertical during integration operations. (Credit: JAXA)
For Japanese launches, the start of the mission is designated X0, rather than T0 as is more common for Western launches. The first stage’s two LE-9 engines ignited a few seconds before X0, with the SRB-3 boosters igniting and the rocket lifting off at the zero mark in the count. The SRB-3s burnt out and separated from the vehicle at one minute and 56 seconds after liftoff, with separation of the payload fairing succeeding at three minutes, 34 seconds mission elapsed time.
First stage flight continued until X+4 minutes, 58 seconds, when main engine cutoff, or MECO, occured. The LE-9 engines then shut down, having completed their role in the mission, with stage separation taking place seven seconds after MECO.
The next flight event and the point at which H3’s previous launch failed – second-stage ignition – successfully took place 12 seconds after staging. This marked the start of an 11-minute, 19-second burn for the LE-5B-3 engine which injected H3’s second stage into LEO. CE-SAT-1E was then deployed 21 seconds after the end of the second stage burn, with TIRSAT separating around 500 seconds later.
After completing almost a full orbit, the second stage restarted to deorbit itself and VEP-4 to a safe reentry over the Indian Ocean. Ignition commenced at X+1 hour, 47 minutes, and 13 seconds, with the burn lasting 26 seconds.
The mission’s final objective was to test the separation mechanism securing VEP-4 to the second stage. To ensure that VEP-4 is not left in orbit as space junk, this test took place about 40 seconds after the end of the deorbit burn.
In addition to its separation mechanism, the payload is also secured to the rocket by stopper bolts, allowing it about one centimeter of motion, which prevents it from drifting away once the separation test is conducted.
This successful test flight will begin to pave the way for H3 to start carrying operational payloads, with several more missions slated to fly before the end of the year. These will carry the ALOS-4 resource-monitoring satellite, a military communications satellite, and the QZS-5 navigation satellite. Over the next few years, H3 will deploy multiple HTV-X cargo spacecraft to supply the International Space Station as well as launch missions to the Moon and Mars.