Possible European systems for space situational awareness

As defined by ESA, space situational awareness (SSA) is the understanding and maintained awareness of the Earth orbital population, the space environment and possible threats to space assets. Space situational awareness is then understood as an upper-set of space surveillance. European SSA is relatively poor and many studies are performed in that domain to propose an autonomous system.This paper will present the required functions for such system derived from SSA definition and a comprehensive survey of technical solutions to fulfil these functions: Survey and tracking to acquire and maintain an orbital parameters catalogue and perform collision avoidance or predict re-entries, characterisation of space objects and acquisition of space environment knowledge. Both ground-based and space-based solutions will be envisaged depending on target orbit types.From this analysis, possible architectural solutions will be proposed and discussed in terms of critical issues.