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HTV-8 (H-II Transfer Vehicle)/Kounotori-8 Mission

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Developed and built in Japan, the H-II Transfer Vehicle (HTV) known as "Kounotori (meaning 'white stork' in Japanese)" is an unmanned cargo transfer spacecraft that delivers supplies to the International Space Station (ISS). "Kounotori" provides very basic support for ISS operations by delivering up to six tons of cargo and has the world's largest transportation capacity. It also has the unique function of carrying multiple numbers of large-size experimental instruments on one flight. 1)

Launch: On 24 September 2019 at 16:05 UTC on Japan’s Kounotori H-II Transfer Vehicle’s eighth journey to the International Space Station aboard an H-IIB carrier rocket has begun following a successful second attempt. The launch from the Tanegashima Space Center followed a standdown due to a pad fire during its initial countdown two weeks ago. Mitsubishi Heavy Industries, Ltd. (MHI) launched the H-IIB Launch Vehicle No. 8 (H-IIB F8). H-IIB F8 flight proceeded nominally. Approximately 15 minutes 2 seconds after launch, as planned, the payload separated from the launch vehicle. 2)

Orbit: Near circular orbit, altitude of ~400 km, inclination = 51.6º.


Figure 1: A Japanese H-2B rocket lifts off with the eighth HTV resupply freighter (image credit: MHI/JAXA)

Kounotori is designed to carry both pressurized and unpressurized cargo to the Space Station in two compartments. The Pressurized Logistics Carrier (PLC) is located at the nose of the spacecraft and incorporates the Common Berthing Mechanism that will secure it to the station. Once berthed, astronauts will enter the PLC and access its cargo. 3)

Behind this, the Unpressurized Logistics Carrier (ULC) contains an Exposed Pallet with additional cargo to be accessed from outside of the station. For the Kounotori-8 mission, a Type III Exposed Pallet will be used, which is designed to be used in conjunction with the Mobile Base System on the US Orbital Segment. The other type of pallet, Type I, is designed instead to be mounted to the Exposed Facility of the Japanese Kibo module.

The Exposed Pallet is loaded with six Orbital Replacement Units (ORUs) for batteries on the station’s Integrated Truss Structure (ITS). These consist of lithium-ion batteries which will replace the original nickel-hydrogen units that launched with the truss segments.

CanadArm2, the space station’s robotic arm, and its Dextre attachment are used to extract the pallet from Kounotori, and to reinstall it prior to departure.

The HTV-8 cargo freighter is loaded with more than 4.1 tons of batteries, experiments, spacewalk equipment, water and provisions for the International Space Station. The Kounotori-8 spacecraft will approach the Space Station in autopilot mode on 28 September (Saturday) and bring the spacecraft to a berthing port on the station’s Harmony module. The crew inside the station will get to work unpacking 2,410 kg of cargo inside the HTV’s pressurized logistics carrier. Meanwhile, robots outside the station will extract a pallet from the HTV’s unpressurized cargo bay containing six lithium-ion batteries to upgrade the space station’s power system. 4)


Figure 2: Japan’s HTV-8 supply ship is seen during launch preparations at the Tanegashima Space Center (image credit: JAXA)

Astronauts Nick Hague and Andrew Morgan on the space station will conduct five spacewalks — the first is set for 6 October — to begin installing the fresh batteries, which will replace aging and less-capable nickel-hydrogen batteries on the P6 solar array module on the far port side of the station’s truss backbone.

The Kounotori-8 mission will deliver the third set of six lithium-ion batteries to upgrade the space station’s four huge U.S.-built external power modules, each of which features solar array wings that span 73 m tip-to-tip. The sixth HTV mission in 2016 carried the first set of new batteries to the station, followed by a second batch last year on the Kounotori-7 resupply mission.

A final set of six batteries will launch on the ninth HTV flight next year.

Each solar array section powers two electrical channels with 12 charging nickel-hydrogen batteries, and NASA is replacing the old batteries in power truss section with six lighter, more efficient lithium-ion batteries.


Figure 3: Six new lithium-ion batteries are loaded on a cargo pallet riding inside Japan’s Kounotori-8 spacecraft (image credit: JAXA)

The Pressurized Logistics Carrier incorporates a new racking system developed for the next-generation HTV-X spacecraft, which increases the number of Cargo Transfer Bags that can be carried from 248 to 316. Each bag measures 50.2 x 42.5 x 24.8 cm, providing a volume of about 50 liters . The cargo includes provisions and fresh food for the space station’s crew, as well as experiments that will be conducted in the station’s Japanese Experiment Module (JEM), Kibo.

JAXA uses the HTV missions as part of its contribution to the space station program. Each HTV cargo freighter measures about 10 meters long and about 4.4 meters in diameter.

The Kounotori-8 mission is also carrying food, fresh drinking water, a high-pressure gas tank to recharge the space station’s internal atmosphere with oxygen and nitrogen, and spacewalking tools, such as high-definition cameras and equipment for a series of repair spacewalks planned later this year for the Alpha Magnetic Spectrometer-2 cosmic ray experiment.

The HTV-8 will also deliver research payloads to the space station.

One of the experiments will demonstrate a high-speed satellite laser communications system, developed by JAXA and Sony Computer Science Laboratories. The technology demonstrator will test a laser link with a ground station, which can accommodate higher-bandwidth communications than radio systems.

“This technology, which employs a laser for in-orbit mass-data communication, will likely be widely used not only in the telecommunications industry, but in the future as a means of communication in the field of exploration,” said Koichi Wakata, a JAXA vice president, in a statement. “Specifically, it can be used as a means of communication between the Earth and the International Space Station, the moon, and Mars. There is a wide range of potential applications, such as communication with the moon rovers.”

The SOLISS (Small Optical Link for International Space Station) experiment will be mounted on an experiment platform outside the space station’s Japanese Kibo laboratory module.

“Sony CSL is taking advantage of the in-orbit demonstrations to complete our long-distance laser communication system,” said Hiroaki Kitano, president of Sony CSL. “It will be the first step for Sony to build upon the results of these demonstrations and put it into practical use in society as we commercialize it.

“The opportunity to use Kibo for the in-orbit demonstrations makes it possible to greatly advance the research and development of the optical communication system, much more quickly than if we had launched a small satellite for the same purpose on our own,” Kitano said. “The SOLISS system is built using consumer components. After the demonstrations, we will retrieve the SOLISS unit and perform follow-up analyses, which we expect will further accelerate our commercialization process.”

JSSOD (JEM Small Satellite Orbital Deployer) and Ultra-small Satellite (CubeSat). An ultra-small satellite collaboratively developed by Kyushu Institute of Technology and National Authority for Remote Sensing and Space Science (NARSS) as well as other ultra-small satellites developed by Space BD Inc. and The University of Tokyo will be transported and deployed from the KIBO.

Japan’s Hourglass experiment also launched on the eighth HTV mission to help scientists investigate the behavior of soil and rock particles under low gravity, simulating the conditions future probes might encounter on a small planet or asteroid.

New hardware for a cellular biology experiment rack is also flying to the space station on the Kounotori-8 spacecraft, expanding the station’s capabilities for biological research.

• Three CubeSats are also riding to the station inside the Kounotori-8 spacecraft. Once they arrive at the station, astronauts will transfer them to the Japanese Kibo module, where they will install them into a deployer for release into orbit through an airlock.

- The 1U NARSSCube-1 nanosatellite was developed by Egypt’s National Authority for Remote Sensing and Space Science in partnership with the Kyushu Institute of Technology in Japan. It carries a low-resolution imaging camera.

- The AQT-D (AQua Thruster-Demonstrator) 3U CubeSat with a mass of 3.7 kg will demonstrate a water-based satellite propulsion system. The AQT-D mission is led by the University of Tokyo (see AQT-D description on the eoPortal).

- RWASAT-1 (The University of Tokyo/Ministry of Commerce, Industry, & Tourism Rwanda Utilities Regulatory Authority Smart Africa secretariat (Republic of Rwanda)). For human resources development of researchers in Republic of Rwanda and technological improvement. A radio wave (weak) receiver is installed and collects sensor information on the ground.

Kounotori will remain berthed until November, as the crew unloads its cargo and replaces it with material and hardware to be disposed of. At the end of its stay, CanadArm2 will be used to remove Kounotori from its berth and release it away from the station.

Mission status

• September 28, 2019: Ground controllers successfully installed the Japan Aerospace Exploration Agency (JAXA) Kounotori 8 H-II Transfer Vehicle (HTV-8) to the Earth-facing port of the International Space Station’s Harmony module at 10:09 a.m. EDT. 5)


Figure 4: International Space Station Configuration. Five spaceships are attached to the space station including Japan’s HTV-8 cargo craft with Russia’s Progress 73 resupply ship and Soyuz MS-12, MS-13 and MS-15 crew ships (image credit; NASA)

- Named Kounotori, meaning “white stork” in Japanese, the craft delivered six new lithium-ion batteries and corresponding adapter plates that will replace aging nickel-hydrogen batteries for two power channels on the station’s far port truss segment. The batteries will be installed through a series of robotics and spacewalks the station’s crew members will conduct later this year.

- Additional experiments on board HTV-8 include an upgrade to the Cell Biology Experiment Facility (CBEF-L), a small-sized satellite optical communication system (SOLISS), and a payload for testing the effects of gravity on powder and granular material (Hourglass).

1) ”HTV8 Mission,” JAXA, 25 September 2019, URL:

2) ”Launch Result of the H-II Transfer Vehicle KOUNOTORI8 aboard the H-IIB Vehicle No. 8,” MHI, 25 September 2019, URL:

3) William Graham, ”HTV-8 launches on H-IIB to the ISS,” NASA, 24 September 2019, URL:

4) Stephen Clark, ”Fresh batteries, experiments on the way to the International Space Station,” Spaceflight Now, 24 September 2019, URL:

5) Nora Moran, ”Japan’s Kounotori Spaceship Attached to Station,” NASA, 28 September 2019, URL:

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (

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