I need to define systems and sub systems of a Fire fighting turtlebot and come up with a state space representation.

I need to define systems and sub systems of a Fire fighting turtlebot and come up with a state space representation. There will be no obstacles, the robot just needs to detect a burning candle in some empty enclosure and establish a direct path toward it. (Don't need obstacle detection planning) Flame will be put out by a fan. Not sure what variables to choose even for SS modeling for localizing (i.e go towards increasing light intensity? decreasing range function towards target? is it different to model a robot just going a specified distance from start (increasing) vs one moving toward a target (decreasing distance) ?