Spacecraft Power SystemsSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Spacecraft Power SystemsSpacecraft Power Systems•Power Source–Table 11-33 compares common s/c power sources–Photovoltaic Cells•Cell types•Sizing (Peak and Average Power)•Radiation Environment•Thermal Environment•Shadowing•Mission life•Degradation characteristicsSpacecraft Power Systems•Power Source–Radioactive Power Sources•Radioisotope Thermoelectric Generators (RTGs)•Nuclear Reactor–Dynamic Power Sources•Brayton, Stirling, Rankine cycles–Fuel Cells•Energy from oxidation reactions•High efficiency, short duration missionsSpacecraft Power Systems•Energy Storage –Physical Constraints•Size•Mass•Operating position•Static and dynamic environments–Programmatic Constraints•Cost•Mission–Power required, eclipse frequency and length•Reliability•MaintainabilitySpacecraft Power Systems•Energy Storage –Electrical Constraints•Voltage•Current Loading•Duty cycles (length and frequency)•Depth of discharge•Activation timeSpacecraft Power Systems•Power Distribution–Cabling•10-25% of power system mass•Volume and location constraints–Fault Protection•Detection•Isolation•Correction–Switching•Subsystems require different amounts of power at different times•Power from batteries, arrays, RTG’s etc.Spacecraft Power Systems•Power Regulation and Control–Peak Power Tracking (PPT)•Non-dissipative •DC-DC converter in series with solar arrays–Direct Energy Transfer (DET)•Dissipative•Shunt regulator in parallel with