H-II Transfer Vehicle

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H-II Transfer Vehicle
Iss020e0413802 - cropped.jpg
H-II Transfer Vehicle (HTV-1) approaching the ISS
Country of originJapan
ApplicationsAutomated cargo spacecraft to resupply the ISS
Spacecraft typeCargo
Launch mass16,500 kg (36,400 lb)[1]
Dry mass10,500 kg (23,100 lb)[2]
VolumePressurized: 14 m3 (490 cu ft)
Length~9.8 m (32 ft) (including thrusters)
Diameter4.4 m (14 ft) [2]
Payload to ISS
Mass6,000–6,200 kg (13,200–13,700 lb)[1][3]
StatusRetired (original model)
In development (HTV-X)
On order1
Maiden launch10 September 2009
Last launch20 May 2020

The H-II Transfer Vehicle (HTV), also called Kounotori (こうのとり, Kōnotori, "Oriental stork" or "white stork"), is an expendable, automated cargo spacecraft used to resupply the Kibō Japanese Experiment Module (JEM) and the International Space Station (ISS). The Japan Aerospace Exploration Agency (JAXA) has been working on the design since the early 1990s. The first mission, HTV-1, was originally intended to be launched in 2001. It launched at 17:01 UTC on 10 September 2009 on an H-IIB launch vehicle.[4] The name Kounotori was chosen for the HTV by JAXA because "a white stork carries an image of conveying an important thing (a baby, happiness, and other joyful things), therefore, it precisely expresses the HTV's mission to transport essential materials to the ISS".[5] The HTV is very important for resupplying the ISS because after the retirement of the Space Shuttle it is the only vehicle that can transfer new 41.3 in (105 cm) wide International Standard Payload Racks (ISPRs) and dispose old ISPRs that can fit the 51 in (130 cm) wide tunnels between modules in the US Orbital Segment.


The inside view of the Pressurised Logistics Carrier section of HTV-1.
The Canadarm2 removing unpressurised payload from HTV-2.
The four main thrusters. Smaller attitude control thrusters can be seen at the right side of this view of HTV-1.

The HTV is about 9.8 metres (32 ft) long (including maneuvering thrusters at one end) and 4.4 metres (14 ft) in diameter. Total mass when empty is 10,500 kilograms (23,100 lb), with a maximum total payload of 6,000 kilograms (13,000 lb), for a maximum launch weight of 16,500 kilograms (36,400 lb).[2]

The HTV is comparable in function to the Russian Progress, ESA ATV, commercial Cargo Dragon 1, and Cargo Dragon 2 of SpaceX. Plus the Cygnus spacecraft, all of which bring supplies to the ISS. Like the ATV, the HTV carries more than twice the payload of the Progress, but is launched less than half as often. Unlike Progress spacecraft, Cargo Dragon 2's and ATV's which use the docking ports automatically, HTVs and American Dragon 1 approach the ISS in stages, and once they reach their closest parking orbit to the ISS, crew grapple them using the robotic arm Canadarm2 and berth them to an open berthing port on the Harmony module.[6]

The HTV has an external payload bay which is accessed by the robotic arm after it has been berthed to the ISS. New payloads can be moved directly from the HTV to Kibō's exposed facility. Internally, it has eight International Standard Payload Racks (ISPRs) in total which can be unloaded by the crew in a shirt-sleeve environment. After the retirement of NASA's Space Shuttle in 2011, HTVs became the only spacecraft capable of transporting ISPRs to the ISS. The SpaceX Dragon and Northrop Grumman Cygnus can carry resupply cargo bags but not ISPRs.[citation needed]

The intent behind the HTV's modularized design was to use different module configurations to match different mission requirements.[7] However, to reduce the development cost it was decided to fly the mixed PLC/ULC configuration only.[7]

To control the HTV's attitude and perform the orbital maneuvers such as rendezvous and reentry, the craft has four 500-N-class main thrusters and twenty-eight 110-N-class attitude control thrusters. Both use bipropellant, namely monomethylhydrazine (MMH) as fuel and mixed oxides of nitrogen (MON3) as oxidizer.[8] HTV-1, HTV-2, and HTV-4 use Aerojet's 110 N R-1E, Space Shuttle's vernier engine, and the 500 N based on the Apollo spacecraft's R-4D.[8] Later HTVs use 500 N class HBT-5 thrusters and 120 N class HBT-1 thrusters made by Japanese manufacturer IHI Aerospace Co., Ltd.[9] The HTV carries about 2400 kg of propellant in four tanks.[8]

After the unloading process is completed, the HTV is loaded with waste and unberthed. The vehicle then deorbits and is destroyed during reentry, the debris falling into the Pacific Ocean.[10]


The HTV-2 departing Tanegashima spaceport bound for the International Space Station.

Initially seven missions were planned in 2008–2015. With the extension of the ISS project through 2028, three more missions were added, with the tenth flight seeing an improved, cost-reduced version called the HTV-X.[11]

The first vehicle was launched on an H-IIB rocket, a more powerful version of the earlier H-IIA, at 17:01 UTC on 10 September 2009, from Launch Pad 2 of the Yoshinobu Launch Complex at the Tanegashima Space Center.[12]

As of December 2020, a total of nine missions successfully launched — one each year for 2015–2019 (though there was no launch in 2017, pushing back the latest to 2020) [13] — one fewer total mission than had been planned in August 2013 at the time the fourth HTV mission was underway.[14]

The improved version of the craft HTV-X is planned to be first used for the tenth flight and will perform scheduled ISS resupply duties for 2021-2024 (with a first launch scheduled for February 2022).[15] In addition, JAXA has agreed to provide HTV-X logistic resupply flights to the Gateway mini-space station (launched by either Falcon Heavy or Ariane 6) as part of its Gateway contribution in addition to co-developing a habitation module with the ESA.[16]

HTV Launch date/time (UTC) Berth date/time (UTC)[17] Carrier rocket Reentry date/time (UTC) Outcome
HTV-1 10 September 2009, 17:01:56 17 September 2009, 22:12 H-IIB F1 1 November 2009, 21:26 [18] Success
HTV-2 22 January 2011, 05:37:57 27 January 2011, 14:51 H-IIB F2 30 March 2011, 03:09 [19] Success
HTV-3 21 July 2012, 02:06:18 27 July 2012, 14:34 H-IIB F3 14 September 2012, 05:27 Success
HTV-4 3 August 2013, 19:48:46 9 August 2013, 15:38 H-IIB F4 [20] 7 September 2013, 06:37 [21] Success
HTV-5 19 August 2015, 11:50:49 24 August 2015, 17:28 [22] H-IIB F5 29 September 2015, 20:33 [23] Success
HTV-6 9 December 2016, 13:26:47 13 December 2016, 18:24 H-IIB F6 5 February 2017, 15:06 [24] Success
HTV-7 22 September 2018, 17:52:27 27 September 2018, 18:08 H-IIB F7 10 November 2018, 21:38 [25] Success
HTV-8 24 September 2019, 16:05:05 28 September 2019, 14:09 H-IIB F8 3 November 2019, 02:09 Success
HTV-9 20 May 2020, 17:31:00 25 May 2020, 12:13 H-IIB F9 (last) 20 August 2020, 07:07 Success



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 preliminary called HTV-X.[11][26]

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 rocket.[27][28] As of June 2019, new ISS plans from NASA's Flight Planning Integration Panel have set the launch of HTV-X1 for February 2022, which is on schedule.[29] In 2022 the debut of the HTV-X spacecraft has been furtherly delayed to January 2024.[30]

The HTV-X has a length of 6.2 m, or 10 m with the unpressurised cargo module fitted. The payload fairing adaptor and payload dispenser have been widened from 1.7 m to 4.4 m to allow the pressurized cargo module to be swapped out for alternate modules, to add increased structural strength, and to accommodate the side hatch.[28]

As of 2021, an evolutionary version of HTV-X called HTV-XG is being considered for transferring cargo to the Lunar Gateway as part of the Artemis program.[31]

Former evolutionary proposals[edit]


As of 2010, JAXA was planning to add a return capsule option. In this concept, HTV's pressurized cargo would be replaced by a reentry module capable of returning 1,600 kilograms (3,500 lb) cargo from ISS to Earth.[32][33]

Further, conceptual plans in 2012 included a follow-on spacecraft design by 2022 which would accommodate a crew of three and carry up to 400 kilograms (880 lb) of cargo.[34]

Lagrange outpost resupply[edit]

As of 2014, both JAXA and Mitsubishi conducted studies of a next generation HTV as a possible Japanese contribution to the proposed international crewed outpost at Earth-Moon L2.[35][36] This variant of HTV was to be launched by H-X Heavy and can carry 1800 kg of supplies to EML2.[35] Modifications from the current HTV includes the addition of solar electric paddles and extension of the propellant tank.[35]

Human-rated variant[edit]

A proposal announced in June 2008, "Preliminary Study for Manned Spacecraft with Escape System and H-IIB Rocket" suggested combining HTV's propulsion module with a human-rated capsule for four people.[37]

Japanese space station[edit]

A Japanese space station has been proposed to be built up from HTV modules.[38] This method is similar to how the modules in Mir, as well as many modules of the Russian Orbital Segment of the ISS are based on the TKS cargo vehicle design.[citation needed]


See also[edit]


  1. ^ a b "Overview of the "KOUNOTORI"". JAXA. Archived from the original on 15 November 2010. Retrieved 18 January 2011.
  2. ^ a b c "H-II Transfer Vehicle "KOUNOTORI" (HTV)". Japan Aerospace Exploration Agency. 2007. Archived from the original on 16 November 2010. Retrieved 11 November 2010.
  3. ^ 「こうのとり」(HTV)5号機の搭載物変更について (PDF). 31 July 2015. Archived (PDF) from the original on 22 December 2015. Retrieved 17 December 2015.
  4. ^ "NASA Sets Briefing, TV Coverage of Japan's First Cargo Spacecraft". NASA. Archived from the original on 17 April 2011. Retrieved 3 September 2009. Public Domain This article incorporates text from this source, which is in the public domain.
  5. ^ ""KOUNOTORI" Chosen as Nickname of the H-II Transfer Vehicle (HTV)". JAXA. 11 November 2010. Archived from the original on 22 December 2010. Retrieved 11 November 2010.
  6. ^ Fujimoto, Nobuyoshi (23–26 November 2010). Kibo Utilization Status Update (PDF). 17th Session of the Asia Pacific Regional Space Agency Forum. Archived from the original (PDF) on 17 March 2012. Retrieved 20 June 2019.
  7. ^ a b Miki, Yoichiro; Abe, Naohiko; Matsuyama, Koichi; Masuda, Kazumi; Fukuda, Nobuhiko; Sasaki, Hiroshi (March 2010). "Development of the H-II Transfer Vehicle (HTV)" (PDF). Mitsubishi Heavy Industries Technical Review. Mitsubishi Heavy Industries. 47 (1). Archived (PDF) from the original on 20 July 2015.
  8. ^ a b c Matsuo, Shinobu; Miki, Yoichiro; Imada, Takane; Nakai, Shunichiro (17–21 October 2005). The Design Characteristics of the HTV Propulsion Module. 56th International Astronautical Congress. Fukuoka, Japan. doi:10.2514/6.IAC-05-C4.1.03. Retrieved 20 June 2019.
  9. ^ "宇宙ステーション補給機「こうのとり」3号機(HTV3)ミッションプレスキット" (PDF) (in Japanese). 20 June 2012. Archived (PDF) from the original on 31 October 2012. Retrieved 24 June 2012.
  10. ^ JAXA (2007). "HTV Operations". Archived from the original on 26 January 2011. Retrieved 2 January 2011.
  11. ^ a b 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.
  12. ^ "Launch of the H-IIB Launch Vehicle Test Flight". JAXA (Press release). 8 July 2009. Archived from the original on 11 July 2009. Retrieved 20 June 2019.
  13. ^ "International Space Station Flight Schedule". SEDS. 13 March 2015. Archived from the original on 27 March 2015. Retrieved 15 March 2015.
  14. ^ "International Space Station Flight Schedule". SEDS. 15 May 2013. Archived from the original on 14 July 2013. Retrieved 9 August 2013.
  15. ^ "Koichi Wakata, JAXA vice president and astronaut, helps chart future of ISS and human space exploration". SpaceNews. 27 July 2018.
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  17. ^ "H-II Transfer Vehicle "KOUNOTORI" (HTV) Topics". Japan Aerospace Exploration Agency. Archived from the original on 22 August 2013.
  18. ^ Stephen Clark (1 November 2009). "History-making Japanese space mission ends in flames". Spaceflight Now. Archived from the original on 7 June 2011. Retrieved 13 November 2010.
  19. ^ Stephen Clark (29 March 2011). "Japan's HTV cargo freighter proves useful to the end". Spaceflight Now. Archived from the original on 19 April 2011. Retrieved 21 April 2011.
  20. ^ Stephen Clark (3 August 2013). "Japan launches resupply mission to space station". Spaceflight Now. Archived from the original on 25 September 2013. Retrieved 3 August 2013.
  21. ^ Stephen Clark (9 August 2013). "Japan's cargo craft makes in-orbit delivery to space station". Spaceflight Now. Archived from the original on 14 August 2013. Retrieved 9 August 2013.
  22. ^ "Successful berthing of the H-II Transfer Vehicle KOUNOTORI5 (HTV5) to the International Space Station (ISS)". Archived from the original on 4 November 2016.
  23. ^ "Successful re-entry of H-II Transfer Vehicle "KOUNOTORI5" (HTV5)". JAXA. 30 September 2015. Archived from the original on 1 October 2015. Retrieved 30 September 2015.
  24. ^ JAXA. "HTV6:H-II Transfer Vehicle KOUNOTORI (HTV) - International Space Station - JAXA". iss.jaxa.jp. Retrieved 26 November 2018.
  25. ^ JAXA. "HTV7:H-II Transfer Vehicle KOUNOTORI (HTV) - International Space Station - JAXA". iss.jaxa.jp. Retrieved 26 November 2018.
  26. ^ "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.
  27. ^ 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.
  28. ^ a b 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.
  29. ^ 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.
  30. ^ Eric Berger [@SciGuySpace] (26 October 2022). "The debut of Japan's new ISS cargo supply ship, HTV-X, has been delayed from January 2023 to January 2024. It will launch on Japan's H3 rocket, which also has yet to make its debut" (Tweet) – via Twitter.
  31. ^ JAXA (30 June 2021). アルテミス計画に関する各国の開発状況について (PDF) (in Japanese). Ministry of Education, Cultura, Sports and Technology. Retrieved 9 July 2021.
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  33. ^ "回収機能付加型HTV(HTV-R)" (in Japanese). JAXA. Archived from the original on 26 August 2011. Retrieved 7 September 2011.
  34. ^ Rob Coppinger. "Japan Wants Space Plane or Capsule by 2022". Space.com. Archived from the original on 24 December 2015. Retrieved 25 October 2012.
  35. ^ a b c "International Human Lunar Mission Architecture / System and its Technologies" (PDF). JAXA. 10 April 2014. Archived (PDF) from the original on 15 April 2015. Retrieved 22 January 2015. Public Domain This article incorporates text from this source, which is in the public domain.
  36. ^ "An International Industry Perspective on Extended Duration Missions Near the Moon" (PDF). Lockheed Martin Corporation. 10 April 2014. Archived (PDF) from the original on 15 April 2015. Retrieved 22 January 2015.
  37. ^ Takane Imada; Michio Ito; Shinichi Takata (June 2008). "Preliminary Study for Manned Spacecraft with Escape System and H-IIB Rocket" (PDF). 26th ISTS. Retrieved 25 December 2010.
  38. ^ Sasaki, Hiroshi; Imada, Takane; Takata, Shinichi (2008). "Development Plan for Future Mission from HTV System" (PDF). JAXA. Retrieved 19 July 2016.

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