Begin with the service
Define what the customer needs to observe, how often, and at what useful resolution. Treat orbit and payload choices as hypotheses to compare.
Connect space to Earth
Model downlink assumptions, processing capacity, delivery latency, and ground architecture together. Document missing evidence before promising service levels.
Review the complete mission
A reference architecture should include operational risks, regulatory research, cost assumptions, and an implementation roadmap. Specialist mission analysis is still required.