Reusable rocket takeoff and landing test conducted: Re-test of Epsilon S second-stage combustion also completed

The Japan Aerospace Exploration Agency (JAXA) conducted a takeoff and landing test of the reusable rocket experimental vehicle "RV-X" in Noshiro City, Akita Prefecture. It flew as planned and successfully acquired data. Partial reuse of rocket airframes has been achieved by companies in the U.S., establishing dominance in the launch market through cost reduction and other advantages. RV-X is an effort with an eye toward application to the successor of the "H3" flagship rocket currently in operation. Establishing the technology and subsequently discerning business viability and other factors appear to be the keys to realization. Meanwhile, JAXA conducted a re-test of the combustion test for the second-stage airframe of the "Epsilon S" small rocket under development on the 23rd.

"Gained data that connects to the next step"

The test, aiming to acquire engine reuse technology and flight data, was conducted on the morning of the 11th at JAXA Noshiro Rocket Testing Center. The airframe measures 7.3 meters in total length, 1.8 meters in diameter, and weighs 3.1 tons including fuel. It has a shape resembling a cylinder with a pointed upper end and is equipped with four legs. It first ascended 11 meters vertically, moved 16 meters horizontally, and descended to land, taking 40 seconds which almost exactly to plan.

After the experiment, Research and Development Manager Takashi Ito held a press conference and stated: "As far as I could see, it flew normally. I am relieved that data effectively connecting to the next step was obtained." The experiment was initially scheduled for March 7, but postponements were repeated due to bad weather and problems with the connection mechanism that supplies fuel to the airframe.

JAXA had envisaged conducting a second test at a later date after re-servicing the airframe but announced on the 21st of July that "as a result of post-test inspections and data evaluations, it was confirmed that the intended results were obtained," and "the RV-X flight test series is concluded (with the single test on the 11th)." The obtained data will be reflected in "CALLISTO," a joint flight test with Germany and France to be conducted within this fiscal year, as well as in future research and development.

Reusable rockets are those where, after launch, the first stage or other relevant sections retro-fire to land at a designated location, are recovered, serviced, and launched again. Compared to conventional disposable rockets, they are expected to be useful for cost reduction and environmental measures.

At JAXA, from the late 1990s through the 2000s, the Institute of Space and Astronautical Science conducted a predecessor experiment "RVT" as a "basic experiment for a fully reusable space transportation system." The successor RV-X scaled up the airframe and changed the engine combustion system, among other modifications. "We are acting in the form of a first step eyeing the next flagship rocket (the successor to H3)," said Ito. Preparations began in 2016, and after repeated ground combustion tests, the takeoff and landing test was realized.

After shuttle retirement, U.S. commercial spacecraft set pace

Unraveling history, the first reusable rocket was the U.S. Space Shuttle. Reusing a crewed orbiter and solid rocket boosters, it was said at the start of development in 1972 to significantly reduce costs. It achieved its maiden flight in 1981, but in reality, re-servicing expenses ballooned. Added to this, safety measures strengthened following two fatal accidents accelerated costs, and after 135 flights, it was retired in 2011.

In 2017, U.S. company SpaceX realized the reuse of the first-stage airframe of the large-sized rocket "Falcon 9." Thereafter, by also reusing the "fairing" that covers satellites, it consolidated its dominance in the market. According to a 2018 document by a National Aeronautics and Space Administration (NASA) official, launching per kilogram of weight into low Earth orbit cost 54,500 dollars for the Shuttle, whereas Falcon 9 cost merely 2,720 dollars.

In addition, U.S. company Blue Origin's "New Glenn" succeeded in reusing its first stage in April this year (though satellite orbit insertion by the upper stage failed). On July 10, China recovered the first stage of "Long March 10B" at sea. Domestically, Honda R&D Co., Ltd. (Saitama Prefecture), a subsidiary of Honda, succeeded in the takeoff and landing of an experimental vehicle in June last year. Triggered by Falcon 9, movements toward reuse have become a major trend.

For fuel, Falcon 9 uses kerosene, and the super-large reusable vehicle "Starship" under development as its successor uses methane. In contrast, RV-X adopted liquid hydrogen and liquid oxygen, the same as H3 and its predecessor "H2A." While hydrogen has good fuel efficiency and can make the airframe lightweight, it has a low boiling point and explodes easily, making it difficult to handle. Ito explained at a press conference in February: "We aim to acquire technology while securing high performance and safety." Like H3, the engine adopts the "expander bleed" combustion cycle, which lacks a pre-burner and is easy to control.

Increasing launch frequency remains a key challenge

The efforts of RV-X and CALLISTO may be perceived as following in the footsteps of SpaceX, but Japan sowed the seeds of airframe reuse early on, as in the efforts of RVT. However, this flight test is actually the first in 23 years. Although research and discussions continued, government policy aiming directly at realization never came about. In the meantime, SpaceX established market dominance, and global circumstances completely changed with practical application. A frustrating development to be sure.

The government's current Basic Plan for Space Policy (revised in 2023) clearly states: "In the 2030s, operate the next flagship rocket. By partially reusing the airframe, increase launch frequency and transportation capacity to reduce costs," and "Engage in research and development of next-generation technologies necessary for scaling up, reuse, and cost reduction toward development."

However, reuse is not a simple problem that can be realized merely by refining technology. In addition to developing infrastructure and systems, above all, there is a wall of business viability requiring high-frequency launches to recover investments. While Falcon 9 accomplished 165 launches last year, Japan's large-sized rocket launches remained at six at most even in a busy year (2017). SpaceX launches dozens of small satellites at a time for its own communication service, cumulatively totaling over 10,000, generating massive internal demand.

Asked for his view at a press conference in February, Ito stated: "Unless we stack up launch counts, it will not pay off (be profitable), but unfortunately we have not reached that point yet. First, we will start from examining maintenance person-hours and inspection items until the next flight. If we can reduce those, it will lead to cost reductions. As a first step, I want to construct that basic data with RV-X."

For Japan, it is important to steadily refine technology so that reuse can be realized in the future when prospects for the business environment are established.

"Largest step" toward Epsilon's comeback

The combustion test for the second-stage airframe of Epsilon S was conducted on the morning of the 23rd of July at JAXA Tanegashima Space Center in Kagoshima Prefecture. Explosions occurred during second-stage combustion tests in July 2023 and November 2024, making development difficult due to investigations into their cause and other factors. In February this year, the plan was changed to temporarily revert the second-stage specifications to those close to the conventional Epsilon that ended operation, and the test was based on this. It was burned for just over two minutes as planned, attempting to acquire data necessary for development.

Through the specification change, the second-stage airframe resurrects the model used in Epsilon Launch Nos. 2 to 6 (2016-2022), and this entire airframe is called "Epsilon S Rocket Block 1." However, because parts of the binder that mixes and solidifies fuel particles and the insulation material have become difficult to obtain, these will be replaced with alternative materials. The launch capacity of Block 1 will decrease compared to the originally planned Epsilon S. No. 7, which will be the first launch vehicle, aiming for a launch within the fiscal year.

At a press conference on the 14th prior to the test, Project Manager Takayuki Imoto stated: "Epsilon failed with Launch No. 6, and since Launch No. 5 in 2021, there has been no success for about five years. We are devoting all our strength toward a comeback. This combustion test is the largest step, and if we overcome it, we will get considerably closer to launch."

The explosion in July 2023 occurred at the Noshiro Rocket Testing Center, and the one in November 2024 occurred at the Tanegashima Space Center. This test was conducted after restoring the facility in Tanegashima damaged by the explosion. Regarding the explosion in November 2024, JAXA explained the status of the cause investigation at a press conference on July 14. It is considered highly likely that during combustion of the second-stage airframe, part of the internal rubber insulation broke for some reason, expanding the combustion area of the fuel, and the investigation will continue.