The European Space Agency’s Gaia star-mapping satellite will be built using contractors selected on the basis of both technical expertise and legal residence in Europe, with the former trumping the latter, according to European government officials.

The goal, they say, is to prevent the agency’s time-honored geographic-return policy from forcing Gaia managers to select subcontractors from a given country with little regard for whether they can do the work on time and within budget.

Work on Gaia, which has been on again/off again over the course of the last 10 years, is designed to “take a census of everything that moves” in the Milky Way in a five-year mission scheduled to start in late 2011, according to ESA Science Director David Southwood.

Gaia is a much more ambitious successor to ESA’s Hipparcos satellite that compiled a catalogue of stars in the early 1990s. Gaia will measure the temperature, age and composition of perhaps 1 billion stars, and also compile a list of perhaps 20,000 exoplanets — planets outside the solar system — as well as 100,000 asteroids and comets.

Gaia is budgeted at 557 million euros ($709 million) including the satellite’s construction and launch, ground facilities and five years of operations.

Astrium Satellites, formerly named EADS Astrium, will lead Gaia’s manufacturing team under a contract signed here May 11 and valued at 317 million euros.

Astrium affiliates in Britain, France, Germany and Spain will retain no more than about 37 percent of that sum. The rest will be spent on dozens of subcontractors to be selected in the next six months from throughout ESA’s 17 member governments.

Science is an obligatory program at ESA, with nations contributing based on their gross domestic product. Because all contribute, all expect to see a return on their investment in the form of ESA contracts with their domestic manufacturers, per ESA’s geographic-return rules.

Nations customarily are guaranteed that at least 90 percent of their investment will be redistributed to their domestic industrial base this way each year.

Vincent Poinsignon, Gaia project manager at Astrium Satellites, said Astrium expects to have signed contracts with Gaia component suppliers by early 2007.

Because of the highly specialized nature of a satellite like Gaia, Astrium cannot be certain that the volume of contracts it will sign with its subcontractors will not exceed the approximately 200 million euros it has budgeted.

Geographic-return considerations make contract estimations even more hazardous because of the lack of competition in some nations among potential Gaia suppliers. This is especially true in ESA’s smaller nations.

To avoid a situation in which contractors take advantage of geographic-return rules to dictate terms to Astrium and to ESA, the agency has received permission from its member states to apply a “best practices” measure to assure that every contractor meets Gaia technical standards. Only then will ESA and Astrium begin negotiations on price.

“Once they have demonstrated ‘best practices,’ we can go a little higher on price to meet the geographic-return rules,” said Jacques Louet, ESA’s head of science projects. “We fully expect to organize competitions for almost all contracts, and this presents serious difficulties in some of the smaller countries. We occasionally have to say, ‘No, your industry will not be part of this program,’ despite geographic-return rules.”

Louet conceded that this practice only postpones the problem; it does not eliminate it altogether. As smaller nations build up credits from programs in which their domestic companies are not generating sales, ESA is obliged sooner or later to find work for them. “Of course the problem compounds over time,” Louet said.

Southwood said that to leave some flexibility to Astrium and to ESA as the Gaia contracting team is assembled, ESA and Astrium have agreed to a “Maximum Ceiling Price” for the Gaia contract. Southwood declined to disclose it, but it is more than the 317 million euros cited in the May 11 contract with Astrium.

Southwood said that in 2007, when the final contract value is known and all component suppliers have committed to contract terms and conditions, ESA will transform its Gaia agreement with Astrium into a firm, fixed-price contract.