HTV-X1: Japan's JAXA Launches New Cargo Spacecraft On Debut Mission To ISS

Japan Aerospace Exploration Agency (JAXA) successfully launched the first HTV-X1 cargo spacecraft, atop an H3 rocket from the Tanegashima Space Center at 0000 UTC, on Sunday (Oct. 26). It is expected to arrive at the International Space Station (ISS) for docking on Wednesday (Oct. 29) at about 1550 UTC.

The launch marked the maiden flight of the new generation of Japanese cargo ships and the debut of the H3 rocket’s configuration with four solid rocket boosters (SRBs). This H3 Flight 7 (H3 F7) mission represents a significant milestone in JAXA’s efforts to modernize its ISS resupply capabilities.

The HTV-X is the successor to the H-II Transfer Vehicle (HTV), also known as Kounotori ("White Stork"), which completed its nine missions to the ISS between 2009 and 2020. The new spacecraft was conceived in 2015 to develop a cost-reduced, improved version of the HTV, with a focus on enhanced efficiency and flexibility. It features a modular design, reusing the Pressurized Logistics Carrier (PLC) from the HTV but incorporating a new Service Module that replaces the Unpressurized Logistics Carrier, Avionics Module, and Propulsion Module.

A key design change was the removal of the side hatch for late access cargo, which was initially planned but later abandoned. Instead, unpressurized cargo is now carried on top of the Service Module, allowing for greater payload capacity and improved mission flexibility.

The HTV-X1 spacecraft is 8 meters(m) long (1.2 m shorter than its predecessor) and has a launch mass of 16,000 kg. It can carry a total of 5,820 kg of cargo, consisting of 4,069 kg of pressurized cargo and 1,750 kg of unpressurized cargo, representing a significant increase over the previous HTV's capabilities.

The spacecraft is powered by deployable solar cells, generating up to 1 kW of power, and is designed to remain berthed to the ISS for up to six months. After departure, it can conduct extended free-flight missions for up to 1.5 years, serving as a testbed for autonomous navigation and long-duration system reliability.

The primary mission of HTV-X1 includes delivering a mix of consumables, maintenance gear, and experimental equipment to the ISS. A key payload is the i-SEEP-3B, the latest version of Japan’s exposed experiment platform, which will be robotically installed on the Kibo laboratory module to host small scientific and commercial payloads.

This first flight is not only a resupply mission but also a full-scale demonstration of JAXA’s upgraded power, avionics, and modular service systems under real ISS conditions 

The H3 rocket, developed by Mitsubishi Heavy Industries (MHI), is designed to be a cost-effective and reliable launch vehicle, incorporating 3D-printed components and simplified structures. Its maiden flight in March 2023 ended in failure due to a second-stage engine issue, but subsequent missions have been successful, including a February 2025 launch that deployed the QZS-6 navigation satellite. The H3’s ability to deliver precise orbital insertion into the ISS’s narrow orbital plane makes it an ideal partner for the HTV-X.

"HTV-X enhances transportation capabilities and adds the capability to provide various users with on-orbit demonstration opportunities for up to 1.5 years after leaving ISS until reentry," Mitsubishi Heavy Industries, which builds the HTV-X for JAXA, wrote in a description of the vehicle.

Looking ahead, JAXA plans to extend the HTV-X design for future missions beyond low Earth orbit, including potential logistics support for the Lunar Gateway the space station NASA may build in lunar orbit as part of its Artemis program, and future lunar surface operations. The agency envisions it aiding "post-ISS human space activities in low Earth orbit."

HTV-X joins the stable of ISS cargo vehicles which currently include Russia's Progress vehicle and Northrop Grumman's Cygnus and SpaceX's Dragon, the only reusable craft of the four. The others are designed to burn up in Earth's atmosphere when their missions are over.

The successful launch of HTV-X1 signifies a new era in Japanese space logistics, enhancing international cooperation on the ISS and paving the way for Japan’s continued role in future space exploration.