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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]

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]
Crew capacity0
VolumePressurized: 14 m3 (490 cu ft)
Length~9.8 m (32 ft) (including thrusters)
Diameter4.4 m (14 ft)[2]
Payload to ISS6,000–6,200 kg (13,200–13,700 lb)[1][3]
First launch10 September 2009



Inside view of the Pressurised Logistics Carrier section of HTV-1.
Canadarm2 removing unpressurised payload from HTV-2.

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 10.5 tonnes (23,000 lb), with a maximum total payload of 6,000 kilograms (13,000 lb), for a maximum launch weight of 16.5 tonnes (36,000 lb).[2] The HTV is comparable in function to the Russian Progress, European ATV, commercial Dragon, and commercial 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 capsules and ATVs, which use the docking ports automatically, HTVs and American commercial spacecraft 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 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 Orbital Sciences Cygnus can carry resupply cargo bags but not ISPRs.[citation needed]

The four main thrusters. Smaller attitude control thrusters can be seen at the right side of this view of HTV-1.

The intention of HTV's modularized design was to use different module configuration to match the mission requirement.[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 to 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, -2, and -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 will be loaded with waste and unberthed. The vehicle will then deorbit and be destroyed during reentry, the debris falling into the Pacific Ocean.[10]


HTV-2 departing Tanegashima spaceport bound for the International space station

Initially seven missions were planned in 2008–2015. With the extension of ISS project after 2015 through 2020, three more missions are planned, possibly replacing the tenth flight with an improved, cost-reduced version (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 GMT on 10 September 2009, from Launch Pad 2 of the Yoshinobu Launch Complex at the Tanegashima Space Center.[12]

As of March 2015, five subsequent missions are planned—one each year for 2015–2019[13] —one fewer total mission than had been planned in August 2013 at the time the fourth HTV mission was underway.[14][unreliable source?]

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 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
HTV-1 10 September 2009, 17:01:56 17 September 2009, 22:12 H-IIB F1 1 November 2009, 21:26[18]
HTV-2 22 January 2011, 05:37:57 27 January 2011, 14:51 H-IIB F2 30 March 2011, 03:09[19]
HTV-3 21 July 2012, 02:06:18 27 July 2012, 14:34 H-IIB F3 14 September 2012, 05:27
HTV-4 3 August 2013, 19:48:46 9 August 2013, 15:38 H-IIB F4[20] 7 September 2013, 06:37[21]
HTV-5 19 August 2015, 11:50:49 24 August 2015, 17:28 [22] H-IIB F5 29 September 2015, 20:33[23]
HTV-6 9 December 2016, 13:26:47 13 December 2016, 18:24 H-IIB F6 5 February 2017, 15:06[24]
HTV-7 22 September 2018, 17:52:27 27 September 2018, 18:08 H-IIB F7 10 November 2018, 21:38[25]
HTV-8 2019[13] H-IIB
HTV-9 2020[13] H-IIB
HTV-X Feb 2022[26] H-IIB

Planned successorEdit


In May 2015, Japan's Ministry of Education, Culture, Sports, Science and Technology announced a proposal to replace HTV with an improved, cost-reduced version preliminary called HTV-X.[11][27]

Proposed concept of HTV-X as of July 2015 is:[28]

  • To re-use the design of HTV's Pressurized Logistics Carrier (PLC) as much as possible, except adding a side hatch for late access cargo,
  • To replace the Unpressurized Logistics Carrier (UPLC), Avionics Module, and the Propulsion Module with a new Service Module
  • Instead of loading the unpressurized cargo inside the spacecraft, load them on top of the Service Module.

Re-using the PLC design will allow minimizing the development cost and risk. Concentrating the reaction control system (RCS) and the solar panels to the Service Module will allow simplifying the wiring and piping, to reduce the weight and the manufacturing cost. Loading the unpressurized cargo outside the spacecraft allows larger cargo, only limited by the launch vehicle fairing. The aim is to cut the cost in half, while keeping or extending the capability of existing HTV.[28]

The simplification of overall structure will allow the launch mass of HTV-X to be dropped to 15.5 t (planned) from HTV's 16.5 t, while the maximum weight of cargo will be increased to 7.2 t (net weight 5.85 t excluding support structure weight) from HTV's 6.0 t (net 4.0 t).[29]

In December 2015, the plan to develop HTV-X was approved by the Strategic Headquarters for Space Policy of the Cabinet Office, targeting fiscal year 2021 for the flight of HTV-X1 (Technical Demonstration Vehicle) to be launched by the H3 rocket.[30][29] As of June 2019, new ISS planning dates from NASA's Flight Planning Integration Panel have revealed the flight of HTV-X1 to February 2022, which is on schedule.[31]

With the agreement of Japan-US Open Platform Partnership Program (JP-US OP3) in December 2015 to extend the cooperation of ISS operation through 2024, Japan will provide its share of ISS operation costs with the form of transportation by HTV-X, and also a possibility to develop a small return capsule.[32]

The final form of the HTV-X consists of three modules; a lower 3.5 m long pressurised logistics module nearly identical to that of the HTV elongated by 0.2 m and with a side access hatch added to allow late loading while mated to the rocket, a 2.7 m long central Service Module containing all functions and capable of operating independently of the other modules, two arrays of solar panels generate 1 kW of electrical power as opposed to the 200 W generated by the HTV, in addition the Service Module batteries are capable of providing a peak output of 3 kW compared to the 2 kW of the original and a 1 Mbit/s communication link has been added in addition to the original 8 kbit/s link,[33] the main thrusters have been removed and the HTV-X is purely reliant on Reaction Control System (RCS) motors mounted in a ring around the Service Module and selected service module components have been mounted externally on the top of the Service Module sitting beneath an attached unpressurised cargo module to allow for ease of maintenance access in space. Finally the 3rd module by default is a 3.8 m long unpressurised cargo module, essentially a hollow cylinder with shelves it vastly expands the volume of unpressurised cargo which can be stored compared to the storage compartments built in to the outside of the original HTV and it can be optionally replaced with a different mission payload. 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 accommodate replacing of pressurised module with alternate modules, add increased structural strength and to accommodate the side hatch.[29]

Other payloads being considered to replace the unpressurised cargo module while carrying out ISS resupply missions are an external sensor package, a technology trial of an IDSS airlock with automated station docking as used by the Progress and ATV craft, a trial of rendezvous and docking with a simulated satellite module, a smaller satellite piggybacking the launch to reach ISS orbit, a station return capsule, assembling a beyond earth orbit mission such as lunar lander from smaller modules and acting as a space tug shuttling orbiting unpressurised cargo modules to the ISS allowing stuff such as recyclable materials, excess propellant and spare parts to be stored in orbit for future use rather than discarded.[29]

Former evolutionary proposalsEdit


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 1.6 tonnes (1.8 tons) cargo from ISS to Earth.[34][35][needs update]

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.[36][needs update]

Lagrange outpost resupplyEdit

As of 2014, both JAXA and Mitsubishi conducted studies of a next generation HTV as a possible Japanese contribution to the proposed international manned outpost at Earth-Moon L2.[37][38] This variant of HTV was to be launched by H-X Heavy and can carry 1.8 tons of supplies to EML2.[37] Modifications from the current HTV includes the addition of solar electric paddles and extension of the propellant tank.[37]

Manned variantEdit

A proposal announced in June 2008 suggested combining HTV's propulsion module with a manned capsule for four people.[39]

Japanese Space StationEdit

A Japanese Space Station has been proposed to be built up from HTV modules.[40] 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 alsoEdit


  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 11 August 2011. Retrieved 3 September 2009.
  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 Research and Development Division, Ministry of Education, Culture, Sports, Science and Technology (20 May 2015). 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). Archived (PDF) from the original on 5 June 2015. Retrieved 4 June 2015.CS1 maint: Multiple names: authors list (link)
  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.
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  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". Retrieved 26 November 2018.
  25. ^ JAXA. "HTV7:H-II Transfer Vehicle KOUNOTORI (HTV) - International Space Station - JAXA". Retrieved 26 November 2018.
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  27. ^ "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.
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  31. ^ Gebhardt, Chris (20 June 2019). "Station mission planning reveals new target Commercial Crew launch dates". 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.
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External linksEdit