Subsystems
Entire books have been written to detail each of these subsystems (see Brown). Below are brief descriptions of the subsystems applicable to our spacecraft.
Systems – Not a subsystem in itself, systems engineering ensures all subsystems mesh together to meet requirements. This involves defining the requirements early on, allocating resources, planning and performing tests, and other forms of verification and validation.
Mission design – Also not quite a subsystem but critical to the project nevertheless, mission design involves orbit analysis using Satellite Tool Kit to determine values such as how much power will be generated and how much data can be transmitted to the ground network, and also involves determining spacecraft operational modes.