The development of the CHEOPS mission follows the normal phase model used by ESA (c.f. ECSS standard). It is a waterfall approach where several phases end with a formal review milestone. In the case of CHEOPS the phases are described in the following paragraphs.
Phase A – Feasibility Study
The main goal is to assess the technical and programmatic feasibility of the possible concepts. Phase A ends with the Preliminary Requirements Review (PRR).
Phase B – Preliminary Definition
Phase B expands the phase A study by performing a complete design study of the mission. In this phase the technical requirements are updated (phase B1 to SRR) and a preliminary design shall be verified against project and system requirements (phase B2 to PDR). In the case of CHEOPS phase B is split in phase B1 that ends with the System Requirements Review (SRR) and phase B2 that ends with the Preliminary Design Review (PDR)
Phase C – Detailed Definition
Phase C is dedicated to the detailed definition of the mission to be ready for manufacture. This includes construction and test of first test models. In the current model philosophy of the CHEOPS project, these will be the STM (structural and thermal model) and the EM (electrical model). Phase C ends with the Critical Design Review (CDR).
Phase D – Qualification and Production
Phase D focuses on manufacture, assembly and testing of flight hard- and software including ground segment. Phase D has three associated reviews: the Qualification Review (QR) held during the course of phase D, and Acceptance Review (AR) and Operational Readiness Review (ORR) both held near the end of phase D followed by integration and testing on the launcher.
Phase E – Launch campaign and Mission Operations
Phase E prepares the launch and all orbital operations. Phase E has 4 associated reviews: Flight and Launch readiness review (FRR, LRR), and Commissioning result review (CRR, marking the end of phase E1) plus end-of-life-review (ELR, marking the end of E2).