HTV-X, also known as the , is a Japanese cargo spacecraft of JAXA. The successor to the H-II Transfer Vehicle (HTV) for International Space Station (ISS) resupply missions, it was first launched on 26 October 2025.
Background The HTV-X is manufactured by Mitsubishi Heavy Industries with contributions from Mitsubishi Electric. IHI Aerospace provides the propulsion system and American company Sierra Nevada Corporation provides the Common Berthing Mechanism and hatch kit.
Design HTV-X consists of three main modules, arranged from top to bottom on the launch pad: Unpressurized Cargo Support System (UPCSS): Unpressurized cargo is mounted externally on top of Service Module, rather than inside the spacecraft, allowing larger items limited only by the launch vehicle fairing and increasing capacity compared to the original HTV. Service Module (SM): A unit capable of independent operation. It includes two deployable solar arrays generating 1 kW of power (replacing the original HTV's 200 W side-mounted panels), batteries with a 3 kW peak output (up from 2 kW), and upgraded communications with a 1 Mbit/s link alongside the previous 8 kbit/s channel. HTV-X omits a main engine, using a ring of reaction control system (RCS) thrusters for propulsion, and mounts some components externally for easier astronaut access. Pressurised Module (PM): A section with an internal volume of and a payload capacity of . Identical in design to the original HTV, it is positioned at the bottom of the stack to improve mass distribution.
The HTV-X measures in length. It is launched by the H3 rocket with a payload fairing widened to (in contrast to normal ), and Payload Adapter Fitting (PAF) widened to to allow increased structural strength and accommodate the side hatch.
Reusing the pressurised logistics module design from previous HTV reduces development cost and risk. Concentrating RCS thrusters and solar arrays on the service module simplifies wiring and piping, lowering weight and manufacturing cost. External loading of unpressurised cargo enables larger payloads, limited only by the fairing. The goal is to halve costs while maintaining or extending HTV capabilities. Simplification was expected to reduce launch mass to from HTV's , while increasing maximum cargo mass to from .
Other proposed payloads for replacing the unpressurised cargo module during ISS resupply missions include external sensor packages, an IDSS connector for automated docking, satellite rendezvous trials, piggyback small satellites, station return capsules, assembly of lunar mission modules, and acting as a space tug to store resources such as recyclable materials, excess propellant, and spare parts in orbit for future use.
History In May 2015, Japan's Ministry of Education, Culture, Sports, Science and Technology announced a proposal to replace the HTV with a redesigned, lower-cost successor preliminarily designated HTV-X. The 2015 proposal included the following design choices: Reuse of the design of the HTV's Pressurised Logistics Carrier (PLC) as much as possible Replacement of the Avionics Module and Propulsion Module with a unified Service Module Placement of unpressurised cargo on top of the Service Module rather than within an Unpressurised Logistics Carrier (ULC)
In December 2015, development of HTV-X was approved by the Strategic Headquarters for Space Policy of the Cabinet Office, with the first flight of HTV-X1 (Technical Demonstration Vehicle) targeted for fiscal year 2021 aboard an H3 launch vehicle. , NASA's Flight Planning Integration Panel scheduled the launch of HTV-X1 for February 2022.
Under the Japan-US Open Platform Partnership Program (JP-US OP3) agreement signed in December 2015, which extended cooperation on ISS operations through 2024, Japan agreed to provide part of its contribution to ISS operating costs through HTV-X transportation services and the possible use of a small return capsule.
An early concept included a side hatch on the Pressurised Module to permit late cargo loading, but the final design adopted in 2021 omitted this feature. Late cargo loading remained possible through a Payload Adapter Fitting (PAF) with an opening in the H3 upper stage.
Due to delays in the development of the H3, the first HTV-X launch was delayed until 2025. HTV-X1 was successfully launched on 26 October 2025.
Flights , three flights are planned to resupply the ISS. All times are in UTC. Future events are listed as "no earlier than" (NET) the stated date. Some dates are given in Japanese fiscal year (JFY), which runs from 1 April to 31 March of the numerated year. Mission Launch Docking Undocking Reentry Outcome HTV-X1 26October 2025, 00:00:15 30October 2025, 11:10 6March 2026, 17:00 26 May 2026, 14:09 HTV-X2 Summer 2026 HTV-X3 JFY2027
, HTV-X4, HTV-X5, and HTV-X6 are tentatively planned for launch in JFY2028–2030.
See also
Cargo spacecraft Comparison of space station cargo vehicles
References
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