Unit
- Mission concept: The initial phase where high-level objectives, scientific goals, and operational constraints are identified. Stakeholders define the mission purpose, target destination, and desired outcomes, setting the foundation for all subsequent activities.
- Pre-Phase A (Concept Studies): This phase explores multiple mission architectures, performs rough cost and schedule estimates, and identifies feasible approaches. Trade studies compare alternatives to select the most promising concept for further development.
- Phase A (Preliminary Design): The selected concept is refined. System requirements are defined, key parameters like orbit and mass are locked down, and a preliminary design review (PDR) marks the transition to detailed design.
- Phase B (Detailed Design): Subsystem and component designs are completed, interfaces are precisely defined, and detailed analysis is performed. A critical design review (CDR) ensures that the design is mature and ready for fabrication.
- Phase C/D (Fabrication, Integration, Test): Hardware and software are built, assembled, and tested. Environmental tests simulate launch and space conditions to validate performance and verify that the system meets requirements.
- Phase E (Launch and Operations): The mission enters its operational phase. Launch, orbit insertion, and payload activation are executed. Routine operations and anomaly handling continue through the mission lifetime until disposal.
- Phase F (Disposal): End-of-life activities include deorbiting, passivation, or placing the spacecraft in a graveyard orbit. Proper disposal prevents space debris and complies with international regulations and best practices.
- Iterative nature: Mission design is not strictly linear. Information from later phases can prompt updates to earlier phases, such as revising requirements based on test results. Agile methodologies are increasingly applied to manage this iteration.
- Risk management throughout the lifecycle: Risk identification, assessment, and mitigation are continuous across all phases. Early phases focus on programmatic and technical risks, while later phases emphasize integration and operational risks. Risk boards review mitigation plans, and residual risks are accepted or retired before key milestones.
- Stakeholder engagement and requirements flowdown: Continuous communication with stakeholders ensures that mission objectives are correctly translated into system requirements. Requirements are decomposed from top level to subsystem level, with traceability maintained throughout. Changes are controlled through a formal change management process to avoid scope creep.
- Verification and validation planning: V and V activities begin in Phase A and continue through Phase D. Verification confirms that each requirement is correctly implemented through inspection, analysis, demonstration, or test at component, subsystem, and system levels. Validation demonstrates that the final system fulfills the intended mission objectives under realistic conditions, often during operations.
- Trade studies and design optimization: Trade studies perform systematic comparisons of design alternatives using metrics such as cost, risk, performance, and schedule. They are conducted throughout Phase A and B to select optimal architectures. Results are documented in trade study reports and inform design decisions, ensuring that the chosen solution best meets mission objectives within constraints.
Design Principle
Principle: Iterative Refinement through Design Reviews
Definition: Mission design progresses through successive levels of fidelity, with formal reviews acting as gates. Each review (SRR, PDR, CDR) increases confidence and reduces risk before committing resources.
Application: At each review, stakeholders assess whether requirements are met, risks are acceptable, and the design is mature enough to proceed. For a typical spacecraft, the system requirements review (SRR) validates that top-level requirements are complete and traceable before preliminary design begins.
Quick Revision
- The mission lifecycle includes phases from concept through disposal, each with specific objectives and reviews.
- Pre-Phase A explores alternative concepts, while Phase A/B refine the design to a buildable level.
- Phase C/D involves fabrication, integration, and testing of the flight system.
- Phase E covers launch and operations, and Phase F ensures proper disposal.
- Design is iterative; later discoveries may require revisiting earlier phases.