VAL DE REUIL, France — Engineers at prime contractor Astrium Space Transportation and at the European Space Agency (ESA) are working double and even triple shifts to complete work on Europe’s Automated Transfer Vehicle (ATV) in time for a mid-2007 launch. But ATV’s launch aboard an Ariane 5 rocket, now scheduled for July, depends on so many factors both within and beyond the control of project managers that forecasting a launch date remains difficult, they said.

The billion-dollar ATV, which is designed to carry cargo, water and fuel to the international space station, is generally viewed as the most complex space program undertaken in Europe since the development of the Ariane 5 launch vehicle.

Launched aboard a specially designed Ariane 5 and placed into low Earth orbit by an Ariane 5 EPS upper stage that has never performed this kind of work, the 20,000-kilogram ATV is designed to use U.S. GPS satellite guidance to rendezvous with the space station.

From a distance of about 300 meters, it will switch from GPS to optical sensors for its final approach. It must be capable of stopping on command, withdrawing to its previous position and then advancing slowly toward the station. Most of its functions have double backup, meaning the ATV’s operations can withstand two failures of any of its major systems and still perform.

The first ATV, called Jules Verne, has completed assembly and electrical and acoustic testing at ESA’s Estec technology center in Noordwijk, Netherlands. Thermal-vacuum testing began the week of Nov. 13 and is scheduled to continue until early December, ESA ATV Program Manager John Ellwood said.

A final system-validation test is scheduled to occur in February, including a review of the Functional Simulation Facility that simulates all phases of ATV’s mission. Located at Astrium’s site in Les Mureaux, France, this facility has been the source of most of ATV’s problems over the past year.

Nicolas Chamussy, ATV program manager at Astrium, said the ATV flight simulation software is 10 times more complicated than the flight software that controls an Ariane 5 rocket at launch in terms of the lines of computer coding needed.

At a Nov. 10 briefing here at an ATV test facility, Chamussy said the Astrium ATV team is cautiously optimistic that its simulator has been debugged and will be ready for a mid-2007 launch.

ATV managers recently completed a series of tests of an ATV’s approach to the station here at a naval- and missile-test range owned by the French arms procurement agency, DGA. Inside a 600-meter-long building normally used to test ship designs, a mockup of the docking module of the station was erected aboard a mobile platform and then moved toward optical sensors like those aboard ATV.

Stein Strandmoe, ATV guidance and navigation test manager, said the facility is unique in Europe and, as far as he knows, the biggest in the world. He said ESA had considered erecting an ATV test facility on a river, at an airport or on a rail track before discovering the DGA site here. Strandmoe said the simulated approaches have been successfully completed.

But ATV’s launch schedule depends on more than Astrium’s or ESA’s test schedule.

ATV’s arrival at the station also depends on NASA’s shuttle flight schedule, Russia’s schedule of flights of manned Soyuz and unmanned Progress resupply spacecraft — and even the position of the sun relative to the ATV and the station at the time of docking.

To avoid perturbing the optical sensors, the sun must not be behind the station, or behind the ATV, as it prepares for final approach.

“There are a lot of variables,” Ellwood said Nov. 10. “What I can say today is that I believe we will be ready for a July launch. But system tests must still be completed, and no one has actually tested something quite as complicated as this.”

Ellwood said he is discussing ATV’s schedule on a weekly basis with the Arianespace launch consortium, which is responsible for assuring that ATV is fitted into a 2007 schedule that is already booked solid.

Arianespace Chief Executive Jean-Yves Le Gall said Nov. 13 that the company is confident that even ESA’s traditionally long pre-launch activities at the Guiana Space Center spaceport can be accommodated without disturbing Arianespace’s other launches.

“I don’t want to be in a situation where any of our other launch campaigns are blocked by ATV,” Le Gall said in an interview. “We are still working out the details with ESA, but as of now it does not appear that we will have trouble accommodating ATV and at the same time conducting our other launches.”

Arianespace missed its target of six Ariane 5 launches in 2006; a fifth is scheduled for early December. Le Gall said that in 2007 the company plans six Ariane 5 campaigns, plus the ATV flight.

Peter B. de Selding was the Paris bureau chief for SpaceNews.