Engineering:HTV-X

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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. Designed as the successor to the H-II Transfer Vehicle (HTV) for International Space Station (ISS) resupply missions, it was first launched on 26 October 2025.[1]

Background

The HTV-X is manufactured by Mitsubishi Heavy Industries with contributions from Mitsubishi Electric.[2] IHI Aerospace provides the propulsion system[3] and American company Sierra Nevada Corporation provides the Common Berthing Mechanism and hatch kit.[4]

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.[5]
  • 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)[6] and a payload capacity of 4,070 kilograms (8,970 lb).[7] 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.[7][8]

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.[9] 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).[8]

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.[8]

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 an improved, cost-reduced version preliminarily called HTV-X.[10][11] The proposal of HTV-X in 2015 was as follows:[9]

  • To re-use the design of HTV's Pressurised Logistics Carrier (PLC) as much as possible, except for adding a side hatch for late cargo access after the spacecraft-launch vehicle integration.
  • To replace the Unpressurised Logistics Carrier (ULC), Avionics Module, and Propulsion Module with a new Service Module.
  • To load the unpressurised cargo on top of the Service Module rather than inside the spacecraft.

In December 2015, the plan to develop HTV-X was approved by the Strategic Headquarters for Space Policy of the Cabinet Office, targeting launch in fiscal year 2021 for the flight of HTV-X1 (Technical Demonstration Vehicle) by the H3 Launch Vehicle.[12][8] As of June 2019, NASA's Flight Planning Integration Panel had set the launch of HTV-X1 for February 2022.[13]

With the Japan-US Open Platform Partnership Program (JP-US OP3) agreement in December 2015 to extend cooperation on ISS operations through 2024, Japan will provide its share of ISS operation costs with the form of transportation by HTV-X, and also possible use of a small return capsule.[14]

An early concept included a side hatch of Pressurised Module for late cargo loading, but the final 2021 design removed it; late access now uses the ISS docking hatch, requiring a Payload Adapter Fitting (PAF) with access opening on the H3 rocket’s upper stage.[15]

Due to the delay of H3 development, the launch of the first HTV-X slid to 2025. HTV-X1 was launched successfully on 26 October 2025.[1]

As of 2021, an evolved version of HTV-X called HTV-XG is being considered for transporting cargo to the Lunar Gateway as part of the Artemis program.[16]

Flights

As of April 2025, three flights are planned to resupply the ISS.[17]

HTV Launch date/time (UTC) Berth date/time (UTC) Carrier rocket Reentry date/time (UTC) Outcome
HTV-X1 26 October 2025, 00:00:15[1] 30 October 2025, 11:10[18] H3-24W In progress
HTV-X2 JFY2026[19] H3-24W Planned
HTV-X3 JFY2026[19] H3-24W Planned

As of December 2024, HTV-X4 and HTV-X5 are tentatively planned for launch in JFY2027–JFY2029.[17]

See also

References

  1. ↑ 1.0 1.1 1.2 "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 日本語). JAXA. 26 October 2025.
  2. ↑ Tsujita, Daisuke; Fujiwara, Satoshi; Uchida, Takeshi; Nakajima, Atsushi (December 2021). "Development Status and Future Plans of Next Generation Cargo Transfer Spacecraft HTV-X". Mitsubishi Heavy Industries Technical Review 58 (4). https://www.mhi.co.jp/technology/review/pdf/e584/e584060.pdf. 
  3. ↑ "Error: no |title= specified when using {{Cite web}}" (in ja). JAXA. 12 December 2024. https://humans-in-space.jaxa.jp/news/detail/004376.html. 
  4. ↑ "Ozmens' Sierra Nevada Corporation to Provide Hardware for Japanese HTV-X International Space Station Missions". Sierra Nevada Corporation (Press release). May 31, 2019. Retrieved 2024-09-06.
  5. ↑ "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" (in ja). 6 December 2017. http://www.jaxa.jp/press/2017/12/files/20171206_HTV-X.pdf. 
  6. ↑ Sakashita, Tetsuya; Kamiya, Takashi (July 11, 2010). "How the HTV Cargo Vehicle is Fully Stuffed -Cargo Loading Capability Enhancement and Related Issues-" (in en). 40th International Conference on Environmental Systems. American Institute of Aeronautics and Astronautics. doi:10.2514/6.2010-6046. ISBN 978-1-60086-957-0. https://arc.aiaa.org/doi/10.2514/6.2010-6046. 
  7. ↑ 7.0 7.1 "HTV-X". JAXA. https://humans-in-space.jaxa.jp/en/htv-x/. 
  8. ↑ 8.0 8.1 8.2 8.3 JAXA (14 July 2016). "Error: no |title= specified when using {{Cite web}}" (in ja). http://www.jaxa.jp/press/2016/07/files/20160714_htv-x_01_j.pdf. 
  9. ↑ 9.0 9.1 "Error: no |title= specified when using {{Cite web}}" (in ja). July 2, 2015. http://www.mext.go.jp/b_menu/shingi/gijyutu/gijyutu2/059/shiryo/__icsFiles/afieldfile/2015/07/16/1359656_5.pdf. 
  10. ↑ "Error: no |title= specified when using {{Cite web}}". Research and Development Division, Ministry of Education, Culture, Sports, Science and Technology. May 20, 2015. http://www.mext.go.jp/b_menu/shingi/gijyutu/gijyutu2/071/shiryo/__icsFiles/afieldfile/2015/05/28/1358152_1.pdf. 
  11. ↑ "国際宇宙ステーション計画を含む有人計画について" (in ja). June 3, 2015. http://www8.cao.go.jp/space/comittee/27-kiban/kiban-dai5/siryou2.pdf. 
  12. ↑ "Error: no |title= specified when using {{Cite web}}" (in ja). Strategic Headquarters for Space Policy. 8 December 2015. https://www8.cao.go.jp/space/plan/plan2/kaitei_fy27/kaitei_fy27.pdf. 
  13. ↑ Gebhardt, Chris (20 June 2019). "Station mission planning reveals new target Commercial Crew launch dates". https://www.nasaspaceflight.com/2019/06/station-planning-new-crew-launch-dates/. "The new HTV is known as HTV-X and is now planned to make its inaugural trip to the Station in February 2022." 
  14. ↑ "Japan – United States Space Cooperation and the International Space Station Program". Ministry of Education, Culture, Sports, Science, and Technology. 22 December 2015. http://www.mext.go.jp/b_menu/houdou/27/12/__icsFiles/afieldfile/2015/12/22/1365568_01_1.pdf. 
  15. ↑ "Error: no |title= specified when using {{Cite web}}" (in Japanese). Ministry of Education, Culture, Sports, Science. 9 February 2021. https://www.mext.go.jp/kaigisiryo/content/20210209-mxt_uchukai01-000012703_10.pdf. 
  16. ↑ JAXA (30 June 2021). "Error: no |title= specified when using {{Cite web}}" (in Japanese). Ministry of Education, Cultura, Sports and Technology. https://www.mext.go.jp/kaigisiryo/content/0210630-mxt_uchukai01-000016486_5.pdf. 
  17. ↑ 17.0 17.1 "Error: no |title= specified when using {{Cite web}}" (in ja). Cabinet Office, Japan. 24 December 2024. https://www8.cao.go.jp/space/plan/plan2/kaitei_fy06/kaitei_fy0612.pdf. 
  18. ↑ "Successful berthing of the HTV-X1 to the International Space Station (ISS)". JAXA. 30 October 2025. https://global.jaxa.jp/press/2025/10/20251030-1_e.html. 
  19. ↑ 19.0 19.1 "宇宙基本計画⼯程表 (令和５年度改訂)" (in ja). Cabinet Office. 22 December 2023. p. 45. https://www8.cao.go.jp/space/plan/plan2/kaitei_fy05/kaitei_fy0512.pdf. 
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