System/Subsystem Requirements, Overview Determining requirements –Top level definition of driving requirements –Derived requirements Verification process for driving and derived requirements Example of requirements, driving and derived for specific component

Determining Requirements Systems and Subsystems work together to establish driving requirements –Direct link to Program top level document Part of meeting primary objectives, spelled out in mission/science specification Establish requirement number for traceability Directly affected by systems allocation of resources, both power and mass –Subsystem derived requirements Usually performance driven by component or part of subsystem design in order to meet driving requirements Provide design guidelines

General Subsystem Requirements Subsystems must communicate and interact to insure all requirements are met –Performance derived requirements hardest to determine, draw on engineering experience

Requirements Verification Process Driving requirements verified during I&T as part of Subsystem functional and system level testing Subsystem completes performance testing and signs off on meeting driving requirements Typically how customer measures performance, if not compliant must demonstrate meeting mission objectives or how to correct problem Derived requirements unfold in several ways Functional testing, subsystem demonstrates compliance Performance is measured, indicates requirements are met Analysis, document performance while demonstrating robustness with margin

Example, Requirement Development S/C shall point to an accuracy of 40 microrads Mission Reqt ADCS Component Selection, pointing and accuracy are drivers Driving Reqt Alignment between ADCS components and instruments Derived Reqt Component temperature stability, drift, and calibration Derived Reqt Component temperature stability, gradients causing shift of boresight Derived Reqt Active vs Passive temperature control, power and radiator limitations Derived Reqt IRU Star Tracker