Due to the difficulties encountered in developing the small launch vehicle "Epsilon S," the Japan Aerospace Exploration Agency (JAXA) has announced a change of plan: the second-stage motor of the Epsilon S will revert to that of the conventional Epsilon, which has already been retired from service. The aim is to shorten the period in which Japan has no rocket in operation, with a launch targeted for the next fiscal year. The decision was reported to and approved by the Working Group on Space Development and Utilization of the Ministry of Education, Culture, Sports, Science and Technology (MEXT).
Provided by JAXA
The Epsilon S is still under development, but explosions occurred during static firing tests of the second-stage motor in July 2023 and November 2024; investigation into the cause of the second incident is ongoing. At the working group meeting held on the 4th of this month, JAXA briefed members on the situation, acknowledging that the investigation and formulation of responsive measures were taking time and that it was becoming difficult for the rocket to fulfill its role as a core government launch vehicle and to maintain customer confidence. JAXA also reported that it would review its development plans in order to meet near-future satellite launch demand.
Under the revised plan, the second stage won't use the newly developed model for the Epsilon S but will instead revive and adopt the conventional type. However, some materials used as the binder, which mixes and solidifies fuel particles, and as the insulation material have become difficult to procure, substitutes will be used. The overall configuration of this vehicle type will be called the "Epsilon S Launch Vehicle Block 1."
As a result of the revision, the overall length of the vehicle will be reduced from 27.2 meters to 26.8 meters, and the propellant loaded in the second stage will decrease from 18 tons to 15 tons. Because Block 1 has lower capability than the originally planned Epsilon S, there will be constraints on some of the satellites that can be carried. For example, the Vietnamese Earth observation satellite "LOTUSat-1," which had been planned for launch on the first Epsilon S flight, can still be accommodated, but the satellite itself will need to consume more of its own propellant to reach its final target orbit. The capability is insufficient for the solar observation satellite "SOLAR-C," scheduled for launch in fiscal year 2028, and alternative measures are said to require study.
Provided by JAXA
The combustion test facility at the Tanegashima Space Center (Kagoshima Prefecture) will soon complete recovery construction following the November 2024 explosion. Using that facility, a new static firing test of the second-stage motor will be conducted, and the goal is to launch the Block 1 demonstration vehicle within the next fiscal year. Whether any satellite will be carried on the demonstration vehicle has not yet been decided.
At the working group meeting, Project Manager Takayuki Imoto explained: "It is difficult to speak about what comes further ahead, but first, as step one, we are thinking of steadily achieving a successful (Block 1) launch to build a track record and then recovering as much capability as possible in the next plan." He sought the participants' understanding.
The Epsilon is a three-stage solid-fuel rocket. Together with the large liquid-fuel rocket "H-IIA," which was retired last year, and its successor the "H3," it is designated by the government as a core launch vehicle. It carries small satellites for scientific, Earth observation, and technology demonstration purposes. Six conventional Epsilon rockets were launched from the Uchinoura Space Center (Kagoshima Prefecture) between 2013 and 2022. Vehicles No. 1 through No. 5 succeeded, while the final sixth vehicle in 2022 failed. The rocket keeps costs down by sharing its first stage with the solid rocket boosters used on large launch vehicles and by streamlining vehicle inspection and launch control operations. The first launch of the improved Epsilon S was originally planned for 2023.
H3 to conduct another combustion test of minimum-configuration vehicle within this fiscal year
Meanwhile, the H3 also suffered a launch failure on its eighth flight in December last year, and the investigation into the cause is ongoing. JAXA and Mitsubishi Heavy Industries announced on the 3rd of this month that they would forgo the launch of the H3's ninth flight within the fiscal year, which had been held as a contingency window.
The H3 is planned to achieve its minimum configuration—without solid rocket boosters—with the sixth vehicle currently under development, which will be a first for a domestically produced large launch vehicle. During the combustion test of the sixth vehicle conducted at Tanegashima in July last year, a problem occurred in which the pressure inside the first-stage propellant tank did not rise sufficiently. JAXA disclosed at the MEXT working group meeting on the 4th of this month that a re-test incorporating corrective measures would be conducted within the current fiscal year.
Original article was provided by the Science Portal and has been translated by Science Japan.