Japan has successfully launched its new space freighter from the Tanegashima base in the south of the country.

日本在国土南部种子岛航天基地成功发射新型货运飞船。

The 16.5-tonne unmanned H-II Transfer Vehicle (HTV) is on a mission to re-supply the space station.

Its role is vitally important to the station project, which is set to lose the servicing capability² of the US shuttle fleet next year.

The freighter left Earth atop an H-IIB rocket at 0201 local time on Friday (1701 GMT, Thursday).

Separation from the rocket's upper-stage was confirmed some 15 minutes later.

The HTV mission is being directed by engineers in Tsukuba, Japan, and at the US space agency's (Nasa) mission control in Houston.

The vehicle must conduct a number of tests of its navigation and rendezvous³（约会，约会地点） systems before making a close approach to the International Space Station (ISS).

Docking is not expected to take place until at least day eight of the mission.

The freighter（货船） is carrying about 4.5 tonnes of cargo⁴ on this maiden⁵ flight（首航）. It has the capacity to carry six tonnes.

Over the next few years, the HTV, and the other robotic re-supply ships like it, will be central to the operation of a fully¹ crewed, fully functional⁶ ISS.

"This HTV-1 vehicle is a demonstration⁷ flight to verify its functionality and performance," said Masazumi Miyake, one of the Japanese space agency's (Jaxa) senior officials in the US.

"After completion of this mission we are planning to launch one operational HTV per year on average."

Grab and dock

The flight to orbit marked the first time Jaxa had used the H-IIB rocket, a beefed up version of the existing H-11A launcher.

The rocket incorporates additional solid-fuel boosters and a second main engine on its core stage to achieve significant extra thrust.

Unlike all previous spacecraft to visit the International Space Station (ISS), the HTV will not drive all the way into the orbiting platform.

Instead, the Japanese ship will simply park itself under the bow of the ISS to allow the station's robotic arm to grab it.

The vessel⁸ will then be locked into an Earth-facing docking port on the Harmony (Node 2) connecting module⁹.

Safety will be the primary concern for the ISS astronauts. The robotic vessel will be monitored constantly to see that it is behaving as expected.

"[The astronauts] can command the vehicle to abort¹⁰, to retreat or to hold. They can also command the grapple（抓斗） fixture¹¹ to separate in case there is a failed capture," said Dana Weigel, a US space agency (Nasa) flight director for the mission.

The HTV will remain attached to the ISS for about six weeks while its supplies are unloaded.

In addition to the cargo (3.6t) carried in its pressurised compartment¹² (accessed from inside the ISS), the ship has important cargo (900kg) mounted on a pallet（托盘） in an unpressurised compartment.

These exterior¹³（外部，表面） supplies include two new Earth-observation experiments for the exposed "terrace" of instruments that sits outside Japan's Kibo science module.

Again, astronauts will use the station arm to remove the pallet before handing it across to the Kibo arm, which will then position the new experiments.

As the freighter's supplies are used up, the ship will be filled with station rubbish. Ultimately, it will undock from the ISS and take itself into a destructive dive through the atmosphere somewhere over the south Pacific.

When the US shuttles retire at the end of next year or the beginning of 2011, the ISS project will become dependent on five robotic freighters for its logistics:

• The Russian Progress and European ATV have already demonstrated their flight capability. Four more ATVs have been booked to fly to the station, one a year starting in 2010.

• After the first HTV mission, Japan plans a further six flights through to 2015.

• Two commercial US suppliers, SpaceX and Orbital Sciences, are in the process of developing their Dragon and Cygnus supply ships. The first of these is scheduled to deliver supplies to the ISS no earlier than the end of 2010.

HTV and Dragon are particularly important because of their ability to deliver larger items in their unpressurised compartments¹⁴（间隔，个别室） that would not normally fit through the docking port of a pressurised compartment.