By Jonathan Amos
Science reporter, BBC News
Europe's ATV space truck has been cleared for fuelling, to make it ready for launch towards the end of February.
It takes several weeks to fuel the Automated Transfer Vehicle
The vehicle, which will haul new supplies to the space station, will be loaded with some six tonnes of fuel before being mated with its rocket.
Flight managers will probably consider a firm launch date on 6 February.
Much will depend on the timing of the shuttle Atlantis' forthcoming mission. The orbiter must be clear of the station before the ATV arrives.
"It's a case of juggling all the pieces of a puzzle at the moment," said John Ellwood, the ATV programme manager for the European Space Agency.
"The ATV launch will be in the second half of February - that's all we want to say at the moment. We're not going to put a firm date down most likely until the sixth of February because by then we'll know what the situation is with the shuttle," he told BBC News.
Europe's 'big bird'
The Automated Transfer Vehicle (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.
It will make its own way to the orbiting outpost. The docking will also be automatic. Ground controllers and astronauts will only intervene if there is a systems failure and the likelihood of a collision.
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
Since July 2007, Jules Verne has been at the Kourou spaceport in French Guiana undergoing final assembly and testing.
It has now been moved to the far end of the launch centre's giant S5 integration complex; and the time-consuming - and dangerous - process of filling the vehicle with fuel began on Wednesday.
The ATV will be loaded with about one tonne of "Russian fuel" to be passed over to the ISS for its own use. Jules Verne will also be filled with a further five tonnes of another type of hydrazine-based fuel and oxidiser for its own propulsion system.
The latter will be needed by the truck to take it to the station and then boost the platform to a higher altitude (one of the ATV's key tasks).
Fuelling should be complete in early February, at which time the ATV will be moved to Kourou's final assembly building to be mated with its Ariane 5 launcher.
Meanwhile, the US space agency (Nasa) continues to grapple with the fuel sensor glitch which has held the Atlantis orbiter on the ground since 6 December. The ATV cannot arrive at the ISS until the shuttle has been through to the platform to deliver Europe's Columbus science laboratory.
"There are various constraints," explained John Ellwood. "For example, when we actually come into the station, we have a number of [rehearsal] days just before we actually dock.
"Astronauts will watch what is going on with their emergency red stop button which they can press. So there are conflicts with the crew's time that they have to be there while we are doing our manoeuvres; and they obviously can't do that if Atlantis is still there."
There are two 5-6-day docking windows in March when sunlight conditions are at their optimum; a third one exists in early April as well.
A long delay would put pressure on other Kourou operations
"If the shuttle is late coming off the station, we could loiter before moving in," said Mr Ellwood. "We would use about 20kg of fuel a day doing that, which is nothing really. We're trying to build as much flexibility into all of this as possible.
"We've said to the Americans that we'd like to launch as soon as we can because that then allows Arianespace to get on with their normal business." The rocket operator has a heavy schedule this year and is hoping to make 6-8 flights from Kourou.
One not inconsequential issue is the nature of the dry cargo stored on Jules Verne. Some personal items are tied to specific astronauts in the current ISS Expedition crew. Were the ATV scheduled for a very late arrival at the station, technicians might have to go into the vehicle and change them for supplies specific to the next resident crew.
This can be done up to four days before launch.