Scientists and architects typically use the design process to break a large project down into more manageable parts. The design process is a systematic approach that includes defining the problem, conducting research, brainstorming solutions, developing prototypes, and testing/evaluating the design. This structured method helps to ensure that all components of the project are considered and addressed effectively.
Other options you mentioned, like pseudocode, problem statements, and project briefs, may be used in specific contexts, but the overarching framework for managing complex projects is generally the design process.