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HTV-X, also known as the New Space Station Resupply Vehicle (Japanese: 新型宇宙ステーション補給機, Hepburn: Shingata Uchū Sutēshon Hokyūki), 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.[4]

Background

The HTV-X is manufactured by Mitsubishi Heavy Industries with contributions from Mitsubishi Electric.[5] IHI Aerospace provides the propulsion system[6] and American company Sierra Nevada Corporation provides the Common Berthing Mechanism and hatch kit.[7]

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 2.7-metre-long (8 ft 10 in) 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.[8]
  • Pressurised Module (PM): A 3.5-metre-long (11 ft 6 in) section with an internal volume of 39.6 cubic metres (1,400 cu ft)[9] and a payload capacity of 4,070 kilograms (8,970 lb).[2] Identical in design to the original HTV, it is positioned at the bottom of the stack to improve mass distribution.

The HTV-X measures 8 metres (26 ft 3 in) in length. It is launched by the H3 rocket with a payload fairing widened to 5.4 metres (18 ft) (in contrast to normal 5.2 metres (17 ft)), and Payload Adapter Fitting (PAF) widened to 4.4 metres (14 ft 5 in) to allow increased structural strength and accommodate the side hatch.[2][10]

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.[11] Simplification was expected to reduce launch mass to 15,500 kilograms (34,200 lb) from HTV’s 16,500 kilograms (36,400 lb), while increasing maximum cargo mass to 5,850 kilograms (12,900 lb) from 4,000 kilograms (8,800 lb).[10]

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.[10]

Comparison of uncrewed resupply spacecraft, the original HTV is third from the left, HTV-X is fourth from left

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.[12][13] The 2015 proposal included the following design choices:[11]

  • 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.[14][10] As of June 2019, NASA’s Flight Planning Integration Panel scheduled the launch of HTV-X1 for February 2022.[15]

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.[16]

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.[1]

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.[4]

Flights

As of May 2026, 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.[17]

Mission Launch Docking Undocking Reentry Outcome
HTV-X1 26 October 2025, 00:00:15[4] 30 October 2025, 11:10[18] 6 March 2026, 17:00[19] 26 May 2026, 14:09[20] Success
HTV-X2 Summer 2026[21] Planned
HTV-X3 JFY26[22] Planned

As of December 2024, HTV-X4 and HTV-X5 are tentatively planned for launch in JFY27–29.[17]

See also

References

  1. ^ a b c d e 新型宇宙ステーション補給機（HTV‐X）の開発状況について (PDF) (in Japanese). Ministry of Education, Culture, Sports, Science. 9 February 2021. Retrieved 4 March 2021.
  2. ^ a b c d e f “HTV-X”. JAXA. Retrieved 30 January 2022.
  3. ^ 新型宇宙ステーション補給機 HTV-X1 Mission PRESS KIT (PDF) (in Japanese). JAXA. Retrieved 5 November 2025.
  4. ^ a b c d “H3ロケット7号機による新型宇宙ステーション補給機1号機（HTV-X1）の 打上げ結果” [Launch result of new unmanned cargo transfer spacecraft HTV-X1 aboard H3 rocket flight 7] (Press release) (in Japanese). JAXA. 26 October 2025.
  5. ^ Tsujita, Daisuke; Fujiwara, Satoshi; Uchida, Takeshi; Nakajima, Atsushi (December 2021). “Development Status and Future Plans of Next Generation Cargo Transfer Spacecraft HTV-X” (PDF). Mitsubishi Heavy Industries Technical Review. 58 (4).
  6. ^ 新型宇宙ステーション補給機 （HTV-X）1号機サービスモジュールを報道機関向けに公開 (in Japanese). JAXA. 12 December 2024. Retrieved 3 March 2025.
  7. ^ “Ozmens’ Sierra Nevada Corporation to Provide Hardware for Japanese HTV-X International Space Station Missions”. Sierra Nevada Corporation (Press release). 31 May 2019. Retrieved 6 September 2024.
  8. ^ “新型宇宙ステーション補給機（HTV-X（仮称））プロジェクト移行審査の結果について” [New Space Station Resupply Vehicle (HTV-X (provisional name)) Project Progress Review] (PDF). JAXA (in Japanese). 6 December 2017. Retrieved 20 June 2019.
  9. ^ Sakashita, Tetsuya; Kamiya, Takashi (11 July 2010). “How the HTV Cargo Vehicle is Fully Stuffed -Cargo Loading Capability Enhancement and Related Issues-“. 40th International Conference on Environmental Systems. American Institute of Aeronautics and Astronautics. doi:10.2514/6.2010-6046. ISBN 978-1-60086-957-0.
  10. ^ a b c d JAXA (14 July 2016). ＨＴＶ‐Ｘの開発状況について (PDF) (in Japanese). Archived (PDF) from the original on 15 July 2016. Retrieved 18 July 2016.
  11. ^ a b ＨＴＶ－Ｘ（仮称）の開発（案）について (PDF) (in Japanese). 2 July 2015. Archived (PDF) from the original on 20 July 2015. Retrieved 17 July 2015.
  12. ^ 2016年～2020年のISS共通システム運用経費（次期CSOC）の我が国の負担方法の在り方について (PDF). Research and Development Division, Ministry of Education, Culture, Sports, Science and Technology. 20 May 2015. Archived (PDF) from the original on 5 June 2015. Retrieved 4 June 2015.
  13. ^ “国際宇宙ステーション計画を含む有人計画について” (PDF) (in Japanese). 3 June 2015. Archived (PDF) from the original on 13 July 2015. Retrieved 13 July 2015.
  14. ^ 宇宙基本計画工程表（平成27年度改訂） (PDF) (in Japanese). Strategic Headquarters for Space Policy. 8 December 2015. Archived (PDF) from the original on 20 October 2016. Retrieved 18 July 2016.
  15. ^ Gebhardt, Chris (20 June 2019). “Station mission planning reveals new target Commercial Crew launch dates”. NASASpaceFlight.com. Retrieved 20 June 2019. The new HTV is known as HTV-X and is now planned to make its inaugural trip to the Station in February 2022.
  16. ^ “Japan – United States Space Cooperation and the International Space Station Program” (PDF). Ministry of Education, Culture, Sports, Science, and Technology. 22 December 2015. Archived (PDF) from the original on 8 August 2016. Retrieved 25 July 2016.
  17. ^ a b 宇宙基本計画工程表 （令和６年度改訂） (PDF) (in Japanese). Cabinet Office, Japan. 24 December 2024. Retrieved 21 June 2025.
  18. ^ “Successful berthing of the HTV-X1 to the International Space Station (ISS)”. JAXA. 30 October 2025. Retrieved 31 October 2025.
  19. ^ Wall, Mike (6 March 2026). “Japan’s 1st HTV-X cargo craft leaves the International Space Station (photo)”. Space. Retrieved 22 March 2026.
  20. ^ “Successful Controlled Re-entry of HTV-X1”. JAXA. 27 May 2026. Retrieved 28 May 2026.
  21. ^ “JAXA HTV-X2”. NASA. Retrieved 15 June 2026.
  22. ^ “宇宙基本計画⼯程表 (令和５年度改訂)” [Basic Plan on Space Policy (2023 Revision)] (PDF) (in Japanese). Cabinet Office. 22 December 2023. p. 45. Archived (PDF) from the original on 25 December 2023. Retrieved 26 December 2023.