The Importance of the HTV
After the construction of the ISS by 16 different countries at a cost of $100 billion, the largest space structure ever built installed the final components, the Kibo Japanese Experiment Module in July 2009. This facility enlarged the ISS and gave researchers aboard the ability to study space medicine, biology, make observations of Earth, analyze material production and research communications. In order to facilitate these ongoing studies, a spacecraft was needed to sustain astronauts.
Before the launch of the HTV, the station was primarily supplied by a growing fleet of international spacecraft: the U.S. Space Shuttle and Russia's Soyuz. Additional craft, such as Russia's Progress space freighter and Europe's Automated Transfer Vehicles (ATV) also assisted with unmanned supply runs. However, the Kibo was specifically designed to interact with the HTV.
The HTV has the benefit of being able to supply Kibo's two compartments: an internal experimental facility and a large unpressurized area for external research. At 16 ½ tons, 33 feet long and 14 feet wide, the HTV can haul a stunning six tons of supplies. In addition, unlike the Progress and ATV, the HTV does not directly dock with the ISS. Instead, it flies very close to the station and is captured by the Canadarm2. It then is linked to the station either via the Kibo or the Harmony modules.