The European Space Agency has signed contracts worth over €500 million euros ($791 million) for the European Union-led Global Monitoring for Environment and Security (GMES) programme's second and third Sentinel spacecraft.

GMES will deliver an environmental and security monitoring service and use three spacecraft, each called Sentinel. The first, Sentinel-1, for which the $362 million contract was signed with Thales Alenia Space in June 2007, is to be launched in 2011.

On 17 April the $316 million contract for Sentinel-2, a vegetation imager, is to be signed with EADS Astrium. On 14 April the $482 million deal with Thales Alenia Space was signed for Sentinel-3, which is for oceanography and land monitoring. Both will be launched after 2011.

However, GMES will need more Sentinel spacecraft to assure continuous service. Spare satellites are needed in orbit with the operational Sentinels and further spares are needed on the ground. ESA estimates a requirement for four spacecraft for each Sentinel, for a total of 12. To date ESA does not have the approved budget for these spacecraft. It will request additional money from its member states for the Sentinels' second satellites this November.