H-II Transfer Vehicle


The H-II Transfer Vehicle, also called Kounotori, is an expendable, automated cargo spacecraft used to resupply the Kibō Japanese Experiment Module and the International Space Station. The Japan Aerospace Exploration Agency 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, therefore, it precisely expresses the HTV's mission to transport essential materials to the ISS".

Design

The HTV is about long and in diameter. Total mass when empty is, with a maximum total payload of, for a maximum launch weight of.
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.
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 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.
The intent behind the HTV's modularized design was to use different module configurations to match different mission requirements. However, to reduce the development cost it was decided to fly the mixed PLC/ULC configuration only.
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 as fuel and mixed oxides of nitrogen 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 is loaded with waste and unberthed. The vehicle then deorbits and is destroyed during reentry, the debris falling into the Pacific Ocean.

Flights

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.
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.
, five subsequent missions are planned — one each year for 2015–2019 — one fewer total mission than had been planned in August 2013 at the time the fourth HTV mission was underway.
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. In addition, JAXA has agreed to provide HTV-X logistic resupply flights to the Gateway space station as part of its Gateway contribution in addition to co-developing a habitation module with the ESA.
HTVLaunch date/time Berth date/time Carrier rocketReentry date/time Outcome
HTV-110 September 2009, 17:01:5617 September 2009, 22:12H-IIB F11 November 2009, 21:26
HTV-222 January 2011, 05:37:5727 January 2011, 14:51H-IIB F230 March 2011, 03:09
HTV-321 July 2012, 02:06:1827 July 2012, 14:34H-IIB F314 September 2012, 05:27
HTV-43 August 2013, 19:48:469 August 2013, 15:38H-IIB F47 September 2013, 06:37
HTV-519 August 2015, 11:50:4924 August 2015, 17:28H-IIB F529 September 2015, 20:33
HTV-69 December 2016, 13:26:4713 December 2016, 18:24H-IIB F65 February 2017, 15:06
HTV-722 September 2018, 17:52:2727 September 2018, 18:08H-IIB F710 November 2018, 21:38
HTV-824 September 2019, 16:05:0528 September 2019, 14:09H-IIB F83 November 2019, 02:09
HTV-920 May 2020, 17:31:0025 May 2020, 12:13H-IIB F9 2020
HTV-X1February 2022H3 F3

Planned successor

HTV-X

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.
The proposal of HTV-X as of 2015 is as follows:
Re-using the PLC design will allow minimizing the development cost and risk. Concentrating the reaction control system and the solar panels on the Service Module will simplify the wiring and piping, to reduce the weight and 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 the existing HTV.
The simplification of the overall structure will allow the launch mass of HTV-X to be dropped to 15.5 t from HTV's 16.5 t, while the maximum weight of cargo will be increased to 7.2 t from HTV's 6.0 t.
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 by the H3 rocket., new ISS plansfrom NASA's Flight Planning Integration Panel have set the launch of HTV-X1 for February 2022, which is on schedule.
With the Japan-US Open Platform Partnership Program 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 be given an opportunity to develop a possible small return capsule.
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 capable of operating independently of the other modules, which contains two arrays of solar panels generating 1 kW of electrical power as opposed to the 200 W generated by the HTV, batteries capable of providing a peak output of 3 kW compared to the 2 kW of the original, and a 1 Mbit/s communication link in addition to the original 8 kbit/s link, though the main thrusters have been removed, so the HTV-X is purely reliant on Reaction Control System motors mounted in a ring around the Service Module and selected service module components have been mounted externally on the top; and a 3.8 m long unpressurised cargo module, essentially a hollow cylinder with shelves that vastly expands the volume of unpressurised cargo.
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.
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.

Former evolutionary proposals

HTV-R

, 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 cargo from ISS to Earth.
Further, conceptual plans in 2012 included a follow-on spacecraft design by 2022 which would accommodate a crew of three and carry up to of cargo.

Lagrange outpost resupply

, 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. This variant of HTV was to be launched by H-X Heavy and can carry 1.8 tons of supplies to EML2. Modifications from the current HTV includes the addition of solar electric paddles and extension of the propellant tank.

Human-rated variant

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.

Japanese space station

A Japanese space station has been proposed to be built up from HTV modules. 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.

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