PARIS — The European Space Agency (ESA) will not help finance a third set of Sentinel Earth observation satellites despite the request of its powerful and increasingly omnipresent partner in space policy, the European Commission, according to a senior agency official.

While conscious that the commission needs to find substantial new funding, and soon, for the Global Monitoring for Environment and Security (GMES) program including the Sentinel spacecraft, ESA has already gone beyond its strict mandate by sharing the costs of second copies of three Sentinel radar and optical observation satellites. Coming up with more money for third copies is out of the question, said Volker Liebig, ESA’s director of Earth observation.

“There is no way,” Liebig said in an interview when asked about the near-term financial problems facing GMES and the commission’s search for further ESA support for the Sentinels. “Our ministers made this clear to us at the time they agreed to fund the ‘B’ units. There is just not a possibility of going further, although we are urging the commission to begin investments right away to assure GMES’s continuity.”

As is the case for the Galileo satellite navigation program, its other flagship space effort, the Brussels, Belgium-based commission is finding out that taking ownership of an operational system such as GMES means sizable expenditures as far as the eye can see.

ESA and the commission have already budgeted about 2.3 billion euros ($3.43 billion) to build the Sentinel satellites, launch the first three and build an associated ground infrastructure to handle the data.

The commission’s GMES Bureau had also succeeded, in what European government and industry officials say was a deft maneuver, in finding 150 million euros in seed money for GMES-related services between 2011 and 2013. The commission had hoped this would tide the program over until 2014, when its new seven-year budget cycle starts.

It turns out more money will be needed before then.

ESA governments in November 2008 agreed to break with their usual policy of building only prototype satellites, not recurrent models, by sharing the cost of building duplicate models of the three Sentinel satellites already decided. Adding these B units to the package meant saving about 40 percent over what the satellites would cost if ordered separately, and also provided GMES users with a measure of assurance of data continuity.

ESA officials said at the time that helping kick-start GMES — a broad program of Earth observation for civil, military and commercial use — was worth violating the rule that research-and-development agencies like ESA stick with one-off satellite models.

But the message was clear: ESA’s involvement would stop at the B units. After that, the commission would be on its own.

ESA’s position was so firm that the agency even refused to take part in the launch of the three B-unit models.

A year after ESA’s ministerial conference, the commission is now facing new demands for GMES financing that cannot wait until its new budget cycle that starts in 2014. As a practical matter, most of that funding will not be available until 2015.

GMES program managers have estimated that the program will need some 430 million euros per year in maintenance and operations costs starting in 2014, a figure that includes regular launches of replacement satellites and upgrades to the ground segment.

But as GMES begins to attract users who insist on long-term data availability, the commission has realized it will need to make additional program investments almost immediately. Commission officials have begun to suggest that ESA should share in these expenses.

The three B-unit satellites already under contract will be ready for launch starting in 2014. If one or more fail at launch, a replacement needs to be ready in short order to meet the commitment to uninterrupted data flow.

That is why commission officials have deemed a third version of each of the three Sentinel satellites to be necessary. They have urged that these additional spacecraft be ordered soon enough to take advantage of savings at the prime contractors building the first two models of each Sentinel.

Liebig said ESA has suggested to the commission that 140 million euros be found to order C-unit parts so as to take further advantage of savings offered by the Sentinel contractors, and to avoid a possible nonavailability of parts in 2014. “Parts become obsolete, and if the parts are no longer available, it could force a redesign and raise the cost substantially,” Liebig said.

A second problem is the launch of the B units. To be ready for launch in 2014, ESA normally would contract with a rocket provider at least two years in advance — well before the commission’s next financial cycle begins.

“What they could do is make a down payment of say 50 million euros to secure the launch date,” Liebig said. “The important thing is to get the contract confirmed so that launcher availability is not an issue for the program.”

Liebig has said repeatedly that finding suitable launchers for ESA’s Earth observation satellites has been among the program’s biggest headaches.

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