H-II Transfer Vehicle
||Unmanned spacecraft intended to resupply the Kibō Japanese Experiment Module on the International Space Station and, if necessary, the rest of the station.
||10 m (including thrusters)
|Total Launch Payload:
|Mass at launch:
||Solo flight about 100 hours, stand-by more than a week, docked with the ISS about 30 days
The H-II Transfer Vehicle (HTV), also called Kounotori (こうのとり Kōnotori, "Oriental Stork" or "White Stork"), is an unmanned resupply 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. 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". 
Inside view of the Pressurised Logistics Carrier section of HTV-1.
Canadarm2 removing unpressurised payload from HTV-2.
The HTV is about 10 m long (including maneuvering thrusters at one end) and 4.4 m in diameter. Total mass is 10.5 tonnes, with a 6,000 kilograms (13,000 lb) payload. The HTV are comparable in function to the Russian Progress, European ATV, commercial Dragon, and commercial Cygnus spacecraft, all of which bring or are planned to 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 dock automatically, HTVs and American commercial crafts approach the ISS in stages, and are signaled by ISS crew or ground control to continue from one holding point to the next. Once they reach their closest parking orbit to the ISS, crew grip them using the robotic arm Canadarm2 and berth them to an open berthing port on the Harmony module.
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 are the only vehicles that can carry ISPRs to the ISS.
The four main thrusters. Smaller attitude control thrusters can be seen at the right side of this view of HTV-1.
The baseline configuration, known as the "Mixed Logistics Carrier", uses one pressurized and one unpressurized segment and can carry 7,600 kg of cargo in total and is 9.2 m long. When two pressurized units are used together the cargo decreases slightly to about 7,000 kg, and the overall length is reduced to 7.4 m.
To control the HTV's attitude and to perform the orbital maneuvers such as rendezvous and re-entry, 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. 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. Later HTVs use 500 N class HBT-5 thrusters and 120 N class HBT-1 thrusters made by Japanese manufacturer IHI Aerospace Co., Ltd. The HTV carries about 2400 kg of propellant in four tanks.
After the unloading process is completed, the HTV will be loaded with waste and undocked. The vehicle will then deorbit and be destroyed during reentry, the debris falling into the Pacific Ocean.
As of 2010 It is expected to be launched by 2018.
, JAXA is planning to add a return capsule option. HTV's Pressurized Cargo is replaced by a reentry module capable of returning 1.6 tonne cargo from ISS to Earth.
Further, it is expected to be followed on by 2022 by capsules which accommodate a crew of three and carry up to 880 pounds (400 kilograms) of cargo.
HTV-2 departing Tanegashima spaceport bound for the International space station
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. Six subsequent missions are planned.
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