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H-II Transfer Vehicle
 |
| Description |
| Role: |
Unmanned spacecraft intended to resupply the Kibō Japanese Experiment Module on the International Space Station and, if necessary, the rest of the station. |
| Crew: |
Unmanned |
| Dimensions |
| Height: |
~9.8 m (including thrusters)[1] |
| Diameter: |
4.4 m[1] |
| Spacecraft Mass: |
10,500 kg[1] |
| Total Launch Payload: |
6,000 kg[2] |
| Pressurized Payload: |
5,200 kg[2] |
| Unpressurized Payload: |
1,500 kg[2] |
| Return Payload: |
None[3] |
| Mass at launch: |
16.5 ton[2] |
| Pressurized Volume: |
14 m3[4] |
| Performance |
| Endurance: |
Solo flight about 100 hours, stand-by more than a week, docked with the ISS about 30 days[1] |
| Apogee: |
460 km[1] |
| Perigee: |
350 km[1] |
| Inclination: |
51.6 degrees[1] |
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.
[5] 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".
[6]
Design
Inside view of the Pressurised Logistics Carrier section of HTV-1.
Canadarm2 removing unpressurised payload from HTV-2.
The HTV is about 9.8 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.
[1] 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.
[7]
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, until that capability was expanded with the introduction of
the
SpaceX Dragon in 2012.
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.
[8]
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.
[9] 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.
[9] Later HTVs use 500 N class
HBT-5 thrusters and 120 N class HBT-1 thrusters made by Japanese manufacturer
IHI Aerospace Co., Ltd.
[10] The HTV carries about 2400 kg of propellant in four tanks.
[9]
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.
[3]
HTV-R
As of 2010, 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.
[11][12] It is expected to be launched by 2018.
[13][not in citation given]
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.
[14]
Flights
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.
[15] Six subsequent missions are planned.
[16]
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