By Jonathan Amos
Science reporter, BBC News
Europe is set to launch the biggest, most sophisticated spacecraft in its history.
The Automated Transfer Vehicle (ATV) is an unmanned ship that can carry up to 7.6 tonnes of supplies to the International Space Station (ISS).
Its other primary role is to push the orbiting outpost higher into the sky to keep it from falling back to Earth.
The ATV will launch on an Ariane 5 rocket from the Kourou spaceport in French Guiana at 0403 GMT on Sunday.
Its mission will be a huge statement of capability.
The maiden voyage will announce that Europe now has some important new technical competencies to rival the very best in the space exploration business.
The most notable is the ATV's automatic rendezvous and docking technology - the ship can find its own way to the station and attach itself without any human intervention.
"The ATV is how we contribute to the operations costs of the space station - by taking up several tonnes of logistics," says Alan Thirkettle, the European Space Agency's (Esa) ISS programme manager.
"It's also very important as a development. ATV is a marriage of human spacecraft and satellites. It's a very complicated spacecraft; and European industry has had the opportunity to develop new technologies and new techniques as a result of ATV," he told BBC News.
The vehicle has been dubbed "Jules Verne" for Sunday's flight and will weigh some 20 tonnes at launch. Its booster, the Ariane 5, has had to be specially strengthened for the task.
PUTTING THE ATV ON THE RIGHT PATH TO THE ISS
(1) The Ariane 5's first thrust phase lasts 17 minutes; the strap-on solid boosters and the main stage fall into the Atlantic Ocean
(2) Upper-stage re-ignition occurs 1hour and 2 minutes into the flight, and circularises the 260km orbit. The ISS is about 340km high
At 1 hour and 6 minutes, the ATV is ejected; and a final burn (3) deorbits the upper-stage. The ATV must now raise its own orbit
The rocket will put the vehicle - the size of a double-decker bus - into a 260km-high (160 miles) orbit, underneath and behind the space station. The ATV will then raise its height and edge closer and closer to the platform over a series of orbits.
For the Ariane 5, the mission also marks an important milestone - that of the heaviest single payload it has ever attempted to put in orbit.
The rocket is more used to lofting telecommunications satellites into equatorial orbits that go out to 35,000km above the Earth. For this flight, it will have to take a highly inclined trajectory out over the Atlantic to put the ATV on the correct low-altitude path to the ISS.
The 775-tonne Ariane 5-ES vehicle was rolled to the pad on Friday
Ariane's upper-stage will also have to reignite twice - once to circularise the orbit before ejecting the ship; and a second burn to take itself safely out of the sky and into the Pacific Ocean.
The ATV will essentially then be parked in space. It must wait until Space Shuttle Endeavour has completed its forthcoming mission to the ISS before moving in to make a docking, probably on 3 April.
The ship's own computers will be in charge as an advanced form of GPS and, in the latter stages, optical sensors guide it into position on the end of the Russian Zvezda module.
Mission controllers in Toulouse, France, will keep a watching brief but will not intervene unless they see a problem arising.
Likewise, on the station itself, the astronauts will view the approach but will have no role other than in an emergency. If they do sense danger they can order the ATV to reverse by pushing a large red button on a panel positioned in the Zvezda module.
The ATV will stay at the station for six months. At intervals of 10 to 45 days, the vehicle's thrusters will be used to boost the platform's altitude.
Over time, the ISS crew gradually deplete its stock of food, fuel, water, air and equipment.
"And that's when we also act as a dustbin," explains John Ellwood, Esa's ATV project chief.
"All the stuff that the crew has used during the six months that we are attached, they will put in ATV and then we will dump this in a very controlled re-entry into a completely unpopulated area of the Pacific."
Europe has high hopes for the ATV and its technology. Although astronauts will not launch to the ISS in the ship, the vehicle is human-rated - they can go inside its pressurised vessel without wearing spacesuits.
The ATV is a starting point, therefore, if Europe wants to develop its own independent, crew transportation system.
At the moment, no Esa astronaut can get into orbit without the US space shuttle or the Russian Soyuz vehicle.
At their meeting in The Hague in November, Europe's space ministers will be asked to build on the knowledge gained on ATV by approving a research programme that would investigate further technologies which could be used in a possible future human-launch system.
Cost: Total bill was 1.3bn euros (at least 4 more ATVs will be built)
Total cargo capacity: 7.6 tonnes, but first mission will fly lighter
Mass at launch: About 20 tonnes depending on cargo manifest
Dimensions: 10.3m long and 4.5m wide - the size of a large bus
Solar panels: Once unfolded, the solar wings span 22.3m
Engine power: 4x 490-Newton thrusters; and 28x 220N thrusters