BERGEN, Norway — Europe’s ambitious GMES satellite-based Earth observation program is an estimated $600 million short of what it needs to complete development of satellites already under construction and assure the promised data continuity to users in the period from 2011 to 2014, with potential funding sources drying up with each new development in Europe’s sovereign-debt crisis, European government and industry officials said.

While the budget shortfall is not as acute as that facing the European Union’s other flagship space program, the Galileo satellite navigation project, it will not necessarily be any easier to resolve given the many stresses on European government budgets, officials said. “Sometimes what’s possible is unfortunately less than what’s viewed as necessary,” one government official said of the somber GMES budget picture.

Attending the “Living Planet Symposium” on Earth observation missions here June 28-29, European Space Agency (ESA) and European Commission program managers candidly discussed the short-term problems facing the Global Monitoring for Environment and Security (GMES). None were able to point to a solution that did not involve what now are considered unacceptable program cutbacks that would undermine GMES’s main selling points to prospective users.

GMES features a suite of radar and optical imaging satellites called Sentinels, six of which are under contract. The program has already cost ESA and the European Commission some 2.2 billion euros ($2.7 billion). The European Parliament agreed June 16 to add 107 million euros to that sum to help pay program expenses between 2011 and 2013 and prepare for full service introduction with the new satellites in 2014. But much more will be needed.

In statements and interviews here, government officials said several large expenses for GMES have yet to be financed. All are ostensibly the responsibility of the European Commission. The yet-unpaid charges include the launch of the three so-called “B” units, which are near-identical copies of the first three Sentinel satellites. Also included are components for third copies of the Sentinel spacecraft, to be purchased in advance in order to take advantage of discounts available from industry so long as the first group of satellites is still being built. The total amount yet to be paid will not be known until contracts are signed for the launch services and for the satellite parts purchases, but government officials said it is likely to be around 500 million euros.

Given the hundreds of services to be provided by GMES, the commission also needs to find additional money to stimulate the services, augment existing ground-based facilities and pay for the system’s early operations in advance of the commission’s next seven-year budget cycle, to begin in 2014. Once GMES is up and running in 2014, it is expected to cost 600 million euros a year in operating and maintenance charges, including the regular replacement of satellites that are retired.

Mauro Macchini, acting head of the GMES Bureau in Brussels, Belgium, the European Commission arm tasked with overseeing GMES, said the program has won broad support at the European Parliament and the European Council, as evidenced by the parliament’s recent support for fresh financing. The European Council, representing the 27 European Union member governments, is expected to endorse the proposal in September.

“We know that 107 million [euros] is not sufficient,” Macchini said here June 29. “We will have to see if some additional funds can be mobilized. I agree this is not the best time” given the broader European government budget context.

Up to now, the 18-nation ESA has funded more than two-thirds of the GMES program, with the European Commission funding the rest. The roles are expected to reverse as the program becomes operational and is moved onto the European Commission’s books. In addition to satellites, GMES includes an elaborate ground segment to assure that the massive influx of satellite data is digested and distributed to users with minimal delay. Still further investment will be needed to link Earth observation efforts undertaken by individual European governments, other governments and the private sector to the broader GMES grid.

This last effort — linking European and global third-party satellite programs to the GMES system — is one of the keys to GMES’s future success but up to now has been funded almost as an afterthought. The current one-year program, which is scheduled to end in September, is budgeted at 39 million euros, said Bianca Hoersch, program manager at ESA. ESA has asked the European Commission to fund a one-year extension.

Hoersch said June 29 that, by last count, GMES is being asked to create a network including 15 separate European satellite operators with a combined fleet of more than 40 spacecraft. More than 100 satellite sensors on these spacecraft must find their place in a coordinated GMES effort.

ESA officials expressed sympathy with the European Commission’s GMES budget problems but warned that ESA is preparing for budget problems of its own and is unlikely to come to the rescue.

Volker Liebig, ESA’s Earth observation director, said the agency is bracing for aftershocks from the European debt crisis in the form of demands from some of its member governments for program stretch-outs and possible refusals to pay previously committed amounts. Thanks mainly to GMES and to a series of Earth observation research satellites called Earth Explorers, Earth observation has overtaken launch vehicles as ESA’s single biggest funding line, accounting for an estimated 708.4 million euros in the 2010 budget — or nearly 19 percent of the agency’s total planned spending.

“I would expect that Earth observation will have to pay a certain tribute” to the broader European government-debt problem, Liebig said June 28. “What our member states need now is that spending be stretched to fit within what they can afford. We expect to have lower affordability over the next three or four years. For example, we might need to delay the 7th and 8th Earth Explorer missions.”

Liebig said ESA, which was able to purchase its three “B”-series Sentinel radar and optical satellites for 45 percent less than the virtually identical original models cost by committing to them while the first were still under construction, is urging the commission to seek similar savings by ordering certain components for third versions of the same satellites. In addition to saving money, he said this gives confidence to GMES users that the system’s data will be provided on a continuous basis and not be subject to shut-offs in the event of a satellite failure.

ESA has also agreed to extend the operations of its large Envisat radar satellite, which had been scheduled for retirement in 2010, for three years despite the fact that Envisat is about to exhaust its fuel supply. The satellite will be operated in a slightly lower “drift” orbit that will result in a minor interruption of some services, Liebig said. Operating Envisat costs about 40 million euros per year including data distribution. Continuing its use through 2013 will increase the likelihood that users of Envisat data will see no interruption of service between Envisat and the first Sentinel satellite, Sentinel-1, which is scheduled for launch in 2012.

Envisat was designed before ESA adopted rules about de-orbiting satellites at the end of their lives to reduce the population of orbital debris. The international orbital-debris protocol asks that owners of satellites in low Earth orbit — where most Earth observation spacecraft operate — lower than the altitude of their satellites at retirement so as to assure that they re-enter the atmosphere within 25 years and burn up. Envisat’s fuel tanks are too small to accommodate regular operations and the end-of-life de-orbit maneuver. Its forerunner, the smaller ERS-2 radar satellite, has enough fuel reserves to be de-orbited. ERS-2, in orbit for 15 years and flying without stabilizing gyroscopes since 2001, will be retired in mid-2011.

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