HTV stands for H-II Transfer Vehicle. HTV is an unmanned spacecraft designed and built in Japan. HTV is designed to deliver supplies to the International Space Station (ISS).
The typical mission for HTV starts at the Tanegashima Space Center (TKSC) near Tsukuba, in Japan.
A H-IIB launch vehicle will inject the HTV on a low Earth orbit (LEO). After the separation from the H-IIB second stage, the transfer vehicle is able to navigate independently.
It will take approximately three days for HTV to reach the proximity of the ISS. During this time, it will maintain contact with the Control Center at TKSC (designated as HTV-CC) through the Tracking and Data Relay Satellite System (TDRSS). TDRSS is a network of satellites that allow a spacecraft in LEO to maintain permanent contact with the control center on the ground. HTV will use GPS to position itself at 7 km behind the ISS.
At this point, the berthing phase of the mission starts. HTV will approach the ISS within 500 m and use the Rendezvous Sensor (RVS) to move closer to the ISS. Reflectors that are installed on Kibo will allow HTV to maintain a distance of 10 m below the ISS.
HTV does not have the capability to dock on its own to the ISS (as opposed to the European ATV), so the Canadarm2 robotic arm will be used to grab the transfer vehicle and berth it to the nadir side of the Node 2 module.
While the HTV is berthed to the ISS, supplies from the HTVâ€™s pressurized section are transferred to the space station by the crew, and waste will be loaded from the ISS.
The cargo from the un-pressurized section will be unloaded using the robotic arm and attached either to the Exposed Facility of the Japanese Experiment Module (JEM) or the ISS Mobile Base System.
The HTV mission will end in a similar way to the European ATV: a destructive re-entry above the Pacific Ocean.
Here is some more background information about the HTV. The spacecraft is a cylinder-shaped structure 10 m long and 4.4 m in diameter. It has a total mass of 10,500 kg, of which 6,000 kg is cargo (divided into 4,500 kg pressurized cargo and 1,500 kg un-pressurized cargo). HTV can carry 6,000 kg of waste during the re-entry.
HTV consists of four modules: the Pressurized Logistics Carrier (PLC), the Unpressurized Logistics Carrier (UPLC), the Avionics Module, and the Propulsion Module. The UPLC carries the Exposed Pallet (EP), which can accommodate unpressurized payloads.
The PLC is equipped with a Common Berthing Mechanism (CBM). This will allow the crew present on the station to enter the module in order to unload the supplies and load waste material.
The EP carried by the UPLC can be either Type I or Type III Exposed Pallets. The Type I EPs will carry payloads for the Kiboâ€™s Exposed Facility (EF), while the Type III EPs will be used to deliver the Orbital Replacement Units (ORUs) to the ISS.
The systems in the avionics module enable HTV to execute the autonomous flight to the space station. The module also contains communication and power systems. The thirty-two thrusters installed on the propulsion module provide HTV with the capability to execute orbital adjustments and control the attitude during the mission.
HTV will add to the existing fleet of transfer vehicles that includes the Russian Soyuz and Progress spacecraft, as well as the European ATV. The first HTV mission is scheduled for late 2009.
For more information about HTV, you can visit the H-II Transfer Vehicle page on the JAXA web site.