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Prior to this phase, subsystems which make the system have been defined. Requirements and verification tests for the subsystems are laid down. Functions for each of the subsystems are identified and suitable concepts have been selected in order to achieve these functions. In the development phase, these concepts are further refined, specifically for the system to be designed. Details regarding the realization of the system have to be finalized, in this phase. <br/> <br/>
One of the ways to refine the concepts is to represent the functions to be achieved in terms of flow diagrams. This is explained by the following example. The electrical subsystem is responsible to ensure the supply of power to the system. For this example, let’s assume that uninterrupted supply of 1 A current is needed at 5 V. Generation and regulation of power are functions which are to be met by the electrical subsystem. This can be represented using the following schematic: <br/><br/>img[[File:Diag1.png|center|400px]]img<br/><br/>
Note that the output from power regulation is passed on to relevant sections of the system. At the end of power regulation, 1 A current should be available at 5 V. This is the power of 5W. Let the power generation block give an output of yA at xV and this is to be converted to 1A at 5V by the power regulation block. Please note that, until this stage, we have not selected concepts for each of the blocks. Several concepts of power generation have been discussed [[Power Generation | here]]. Based on the analysis, let solar power be selected as a concept for the power generation. Solar power is harnessed by using solar panels. The amount of power generated will depend on the following factors:
*Configuration of solar panels - number of cells in series and parallel on each panel and the interconnection between panels, if there are multiple panels.
Apart from this, there are several factors like the intensity of radiation, solar cell technology, etc which will affect the power generation. Note that throughout the orbit, uniform power generation may not be assured. Hence, there are is an additional function which needs to be achieved:
*To supply power to power regulation block if power from solar panels is insufficient
This power cannot be generated out of nothing. One way to arrange for this is to store power when it is available in excess and release this power when solar power is insufficient. One of the ways to achieve this is by use of a [[battery]]. Typically, a dedicated circuitry is needed to handle the charging and discharging of the battery. This is represented as the “power storage management” in this updated schematic.<br/>img[[File:Diag2.png|center|600px]]img
The discussion on this example is paused at this point to share some insights on the process followed. While discussing this example, a schematic was created, keeping in mind only the power aspect. The subsystem was broken down to blocks. Concepts required to realise these blocks were understood in detail and requirements were further defined for these blocks. In the process, an updated schematic was also created. Such schematics can be developed for other subsystems as well. Each schematic is designed keeping in mind one or more perspectives, like the flow of power, the flow of data, based on mechanical interfaces etc. These schematics or representations are called system architecture. There could be more than one system architecture which meets the requirements. These alternatives are to be evaluated by further system analysis. <br/> <br/>
Let’s evaluate the starting point for the example as well. The requirement that 1A at 5V is to be supplied to the system is an estimate which is to be arrived at before all the components of the system have been finalized.<br/> <br/>