The Japan Aerospace Exploration Agency (JAXA) is set to launch its advanced HTV-X1 cargo spacecraft to the International Space Station (ISS) from the Yoshinobu Launch Complex at Tanegashima Space Center on Sunday. The launch had been delayed for days due to poor weather at the picturesque launch site.
The mission will utilize JAXA’s H3-24L rocket, an expendable launch system developed by JAXA and Mitsubishi Heavy Industries (MHI) as a successor to the H-IIA and H-IIB rockets.
HTV-X1: A Next-Generation Resupply Vehicle:
The HTV-X1, also built by MHI for JAXA, is an uncrewed, expendable spacecraft designed to resupply the ISS while serving as a platform for technical demonstrations. Japan developed the HTV-X spacecraft as a replacement for the earlier HTV (Kounotori) cargo ship that launched atop the now-retired H-IIB.
The H3 is a medium-lift launch vehicle. Its first stage utilizes two or three LE-9 engines and uses 222 tons of Liquid Hydrogen (LH2) and Liquid Oxygen (LOX), otherwise known as Hydrolox. The second stage uses one LE-5B-3 engine and is powered by 23 tons of Hydrolox.
There is the additional capability of strap-on Solid Rocket Boosters; the H3 rocket can have either two or four SRB-3s.
JAXA’s range of launchers – Credit JAXA
Another JAXA rocket, Epsilon S, uses an SRB-3 as its first stage.
Unlike its predecessor, which required 80 hours for cargo loading, the HTV-X1 streamlines the process to just 24 hours, enhancing mission efficiency.
With a launch mass of 16,000 kg, the HTV-X1 can carry up to 5,820 kg of supplies and experiments using International Standard Payload Racks to optimize capacity. The spacecraft features two solar panel arrays generating 1 kW of power—five times the 200 W capacity of the original HTV.
Onboard power supplies and refrigeration units enable the delivery of fresh food to Expedition 74 and future ISS crews. The HTV-X1 maneuvers using its Reaction Control System (RCS) thrusters.
Mission Operations:
JAXA astronaut Kimiya Yui, a member of Expedition 74, will berth the HTV-X1 to the ISS’s Harmony module using the Canadarm2, a robotic arm developed by the Canadian Space Agency. Yui previously berthed an HTV spacecraft during Expedition 44 in 2015.
HTV-X1 approaching the ISS – Credit JAXA.
Once attached, the HTV-X1 is expected to remain at the ISS for six months. After departing, it has the capability for extended missions, enabling additional scientific and technical experiments.
H3 Rocket: A Reliable Workhorse:
The H3 rocket, which will carry HTV-X1, debuted in March 2023 with the launch of the 3.7-tonne ALOS-3 (Daichi-3) satellite. A second-stage failure triggered the Flight Termination System, marking an initial setback.
Since then, JAXA and MHI have achieved four successful launches, including a February 2025 mission that deployed QZS-6, a regional navigation satellite for Japan.
Looking Beyond the ISS:
With the ISS scheduled for deorbit in 2030, JAXA is preparing for future missions beyond low Earth orbit. The HTV-X is designed to deliver cargo to Gateway, a planned lunar-orbiting space station in a near-rectilinear halo orbit.
JAXA is also contributing to Gateway through the International Habitation (I-Hab) module, developed in collaboration with the European Space Agency. The I-Hab will provide life support for visiting astronauts and is slated to launch on NASA’s SLS Block 1B for the Artemis IV mission in September 2028.
Lead Image: JAXA’s new rocket – credit Mack Crawford for NSF.
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