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Mission design concepts for next generation defence space observation systems

Earth observation from space devoted to civilian users are typically characterized by a variety of needs spanning from the mapping of very large areas of mid resolution up to higher resolution images (metric or even sub-metric) taken on narrower scenes. These needs are even more stringent when considering the defense use of the space observation, which typically require: 1) very high flexibility in terms of capacity to sustain different typologies of images (from wide fields to narrow field at high resolution) acquisition, 2) very high resolution for in-depth technical analysis, 3) stringent timeliness in order to sustain operations even at tactical level, 4) high image acquisition capacity in theatre scenario surveillance expressed in terms of number and typologies of images that can be taken in a single flyby. Nowadays, the space observation systems currently available fulfils these needs quite satisfactory. This increasing needs require a significant evolution of design concept of space SAR constellation, to constitute the 'next generation' space systems for security and defence. Purpose of this paper is to delineate the key points of this evolution, focusing on mission aspects (e.g. orbit constellation design) and possible SAR instrument design characteristics.