Japan's space truck ready to fly

By Jonathan Amos Science reporter, BBC News

Animation of the HTV's launch and payload delivery

Japan is ready to launch its new space freighter from the Tanegashima base in the south of the country.

The 16.5-tonne unmanned H-II Transfer Vehicle (HTV) will haul cargo to the International Space station (ISS).

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

When the orbiters retire, re-supply will be in the hands of a number of robotic vessels - the HTV included.

The logistics demands of a fully crewed, fully functional ISS will require all of the freighters to play their part.

Lift-off for the HTV is timed for 0201 local time on Friday (1701 GMT, Thursday).

"This HTV-1 vehicle is a demonstration 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."

The rocket carrying the cargo ship into orbit - the H-IIB is also new. Japan, though, has high confidence the launcher will work first time.

It is essentially a beefed up version of the existing H-11A vehicle.

The attachment of two additional solid rocket boosters and a second main engine on the core stage will give the IIB the significant extra thrust it needs to hurl the HTV into low Earth orbit.

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

The HTV will be directed to conduct a number of tests of its navigation and rendezvous systems before making a close approach to the ISS.

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

Unlike the European freighter (the Automated Transfer Vehicle - ATV), which made its maiden flight to the ISS last year, the HTV cannot drive itself all the way into the station.

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

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

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 abort, to retreat or to hold. They can also command the grapple fixture 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 4.5 tonnes of supplies are unloaded.

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

These exterior 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 into 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 late 2010.

Length: 9.8m; Diameter: 4.4m; Vehicle Mass: 10.5t; Max cargo: 6t Pressurised cargo: Food, clothing, water, laptops, science equipment, etc External cargo: Equipment to study Earth's oceans and the atmosphere First unmanned vehicle to deliver both pressurised and unpressurised cargo

Jonathan.Amos-INTERNET@bbc.co.uk