Confident that its member states will make good on their financial promises, the European Space Agency (ESA) is preparing to sign contracts for three Earth observation satellites.

It will be the first hardware-development effort in the Global Monitoring for Environment and Security (GMES) initiative being run by ESA and the European Union’s executive commission.

ESA has received only 253 million euros ($303.6 million) of the more than 1.2 billion euros needed to build and launch the satellites.

But informal, non-binding promises from its member governments for an additional 800 million euros — plus the likelihood of money coming from the European Commission — are enough to permit a full start for the three satellites, ESA officials say.

“Our delegations have been extremely supportive of GMES and that support has not been reduced in the past couple of months,” said Peter G. Edwards, ESA’s program manager for the Metop polar-orbiting meteorological satellite program. “It’s true we have only about 250 million euros committed, but we are confident enough in the future support of our governments to begin the three satellites. We run the risk of wasting 250 million euros, but we think that risk is minimal.”

ESA governments’ support for GMES was so strong that when the agency in December asked them for 200 million euros to start one GMES satellite, they signed up for 253 million in payments. Germany and Italy led the backing, followed by France. Another 800 million euros in GMES funding has been promised since the December meeting.

As a result, ESA has decided to solicit bids for three satellites.

Sentinel-1, to be a follow-on for the agency’s radar payloads aboard the ERS-2 and Envisat satellites in orbit, will be contracted this year for a scheduled launch in 2010 or 2011.

Whether the Envisat satellite, launched in 2002, will continue in service that long is questionable, but the satellite up to now has suffered no major onboard failures and has enough fuel and other consumables to continue beyond the end of the decade, according to ESA estimates.

Sentinel-2, which will have a superspectral land-monitoring sensor and will complement the data produced by the U.S. Landsat program, is scheduled for launch in 2011-2012. Sentinel-3, whose principal payload is an ocean-monitoring altimeter and an optical and infrared radiometer, will follow on from the Meris instrument on Envisat and is scheduled for launch in 2011-2012.

ESA previously had expected to have only enough money to begin work on a single multi-sensor satellite to provide data continuity for the ERS-2 and Envisat spacecraft.

ESA estimates that each Sentinel will cost between 250 million and 350 million euros.

Stephen Briggs, head of Earth observation science and applications department at ESA’s Esrin facility in Frascati, Italy, said the Sentinel contracts will include stop-work milestones to permit the agency to suspend its payments in the event the promised funding does not arrive.

Briggs agreed that, given the level of support of ESA governments, the risks in moving forward with investment are small.

ESA has estimated that it will cost around 1.2 billion euros to build and launch the three Sentinel satellites. The agency has almost all of that money in its own committed and promised GMES budget. Operating the spacecraft will require additional funds and this money has been tentatively set aside by the commission of the 25-nation European Union.

But the European Union’s budget, which originally had earmarked 500 million euros per year for “Space and Security,” is facing cuts of around 30 percent.

Briggs said it remains unclear how the budget will be divided between orbital systems and security-related investment that has no space component.

EADS Astrium U.K. of Stevenage and Portsmouth, England, had been tentatively selected as prime contractor for Sentinel-1, but that role may be taken away from the company if the British government does not raise its GMES investment, according to ESA officials.

At the December meeting of ESA governments, Britain agreed to take a less than 5-percent share of GMES, well behind Germany, Italy and France.

The government since has raised its commitment to about 5.5 percent — still too low to permit EADS Astrium U.K. to keep its prime contractor’s role.

ESA’s geographic return principle forces the agency to distribute work shares to companies located in nations according to those nations’ financial stake in the program.