Before revision: These assessment studies are performed in the early phases of mission and spacecraft design; the so called "Phase 0" or "Pre-phase A" of the ESA Project URL in which needs are identified and Mission Analysis is performed.
After revision: These assessment studies are performed in the early phases of mission and spacecraft design; the so-called "Phase 0" or "Pre-phase A" of the ESA Project URL in which needs are identified and Mission Analysis is performed.