This study examines the bacterial flagellum from an engineering viewpoint. This examination concentrates on the structure, proteins, control, and assembly of a typical flagellum, which is the organelle imparting motility to common bacteria. Two very different, independent approaches are applied and then compared in three separate papers: Parts 1, 2, and 3. The first approach is a constructive or top-down approach, covered in this Part 1. It considers the purpose of a bacterial motility system, its typical environment, new and existing required resources, and its physiology. It sets forth the logically necessary functional requirements, constraints, assembly, and relationships. The functionality includes a motility control subsystem and provision for self-assembly. The specification of these requirements is intended to be independent from knowledge of the flagellar structures. This is original material not covered in academic papers on the flagellum. Part 2 will cover the second approach, an analytical or bottom-up approach. It will document the known 40+ protein components and the structure, assembly, and control of a typical flagellum. The bacterial flagellum is a well-researched molecular subsystem. However, in Part 2 the assembly relationships will be illustrated graphically in a form and detail not found in previous literature. Part 3 will compare the two approaches and conclude with several original observations. Those include the coherent assembly orchestration and an ontology of the exceedingly specific protein-binding properties. The latter observation is significant, and it suggests future modeling to elucidate how the strong, coherent, multi-way protein binding is achieved at the molecular level.