By Jonathan Amos
Science reporter, BBC News, Kourou
Engineers working on Europe's space station re-supply truck are aiming to have it ready for flight in February.
The European Space Agency had an early launch target of January, but the final assembly and fuelling sequence of the ATV is proving quite challenging.
Some components have had to be replaced on the vehicle, including elements involved in docking with the outpost.
The ATV has been dubbed Jules Verne for its maiden voyage to the International Space Station (ISS).
It will deliver a little under seven tonnes of air, water, fuel, scientific equipment, food, clothing and even personal items to the platform.
The 20-tonne truck is the biggest, most sophisticated spacecraft Europe has ever attempted to fly; and engineers were under no illusions that the final preparations at the Kourou spaceport in French Guiana would be anything other than tricky.
"We are on track and we are passing milestones, one after another," said Nicolas Chamussy, the ATV programme manager at prime contractors EADS-Astrium.
"We're working a minimum of two shifts; sometimes three shifts, six days a week. But the bird is big and we've still got a lot of tests to do."
SPACE STATION CARGO TRUCKS
ATV (L) will resupply the ISS with up to 7,500kg of cargo
Capacity is three times that of the Russian Progress craft (R)
Deliveries will include science equipment, food and clothing
Large tanks can transport vital air, water and fuel supplies
ATV project's estimated cost is about 1.3bn euros (£0.9bn)
At least four craft will follow the maiden ATV - Jules Verne
Named after the author who wrote about fantastic journeys
The ATV has two major divisions - a pressurised payload unit, and an avionics and propulsion unit. They have yet to be joined and welded in the spaceport's giant integration halls.
And some teething issues have put pressure on the timeline.
The Russian docking mechanism had to be taken off the vehicle so a faulty switch could be replaced.
"The Russian team came and dismounted it," explained Mr Chamussy. "They were missing one millimetre in the setting of one contact. The team re-tuned it, cleaned it and checked it worked. It was not a major problem. The system will be reinstalled two weeks from now," he told BBC News.
There are valves in the propulsion sub-system that need to be exchanged; and components in the light-reflector system used in the final moments of navigation to the station are also having to be replaced because of fears that condensation may have compromised their proper functioning.
But ATV does now have its four solar wings attached, and soon its cargo will be added and the batteries installed. It is hoped the vehicle will be ready for fuelling by mid-December and can be transferred for mating with its rocket at the end of January. The launch would follow sometime in February.
The Ariane 5 rocket has had to be specially modified for the flight. Used to lofting just under 10 tonnes into a highly elliptical geostationary transfer orbit, the rocket will have to put the 20-tonne space truck into a low-Earth circular orbit.
To get the job done, the launcher will be relying on some special manoeuvres from the EPS upper stage and its reignitable Aestus engine.
The package will give the ATV an initial boost over the Atlantic, putting the truck in an orbit with a near distance (perigee) to Earth of 160km and a far distance (apogee) of 250km above the planet.
"Above Australia, we will have a second boost and this will circularise the orbit; it will increase the perigee from 160 to 250km and after this we will jettison the ATV," explained Jean-Yves Le Gall, the boss of Arianespace, the company which operates Europe's rockets.
"There will be a further ignition to organise the re-entry of the EPS over the Pacific Ocean," he told BBC News.
The EPS will put ATV on a circular orbit under the station
The ATV flight is the third event in a series of major space station activities for Europe.
The platform has just taken delivery of the Italian-built Harmony node which is the connecting passageway linking the station to the soon-to-arrive Columbus laboratory.
The European module is currently sitting inside the Atlantis shuttle at the Kennedy Space Center ready for a 6 December launch.
The arrival of the Jules Verne truck in February or March will signal that Europe's involvement in the station project is in full swing.
ATV capacities: Maximum total load is 7,667kg
1,500-5,500kg - dry cargo; 0-100kg - air (oxygen/nitrogen)
0-840kg - drinking water; 0-860kg - refuelling propellant