Astro 331 Electrical Power Subsystem—Intro Lesson 19

1. Astro 331Electrical Power Subsystem—IntroLesson 19 Spring 2005

2. Electrical Power Subsystem—IntroObjectives Objectives • Objective 1. Know the driving requirements for the electrical power subsystem EPS • Objective 2. Know the functions and components of the EPS • Objective 3. Be familiar with the EPS of example spacecraft Reading • SMAD Chapter 11.4 Lesson 19

3. Electrical Power Subsystem—IntroDriving Requirements Lesson 19

4. Electrical Power Subsystem—IntroFunctions • EPS permeates almost all of S/C • S/C relies on EPS for power to: • Make payload operate • Provide communications / data handling • Thermal control • Attitude determination & control • Fire propulsion systems • Deploy mechanisms • Etc., etc., etc….. • Top level design decision: centralized vs. distributed (tradeoff versus efficiency) Lesson 19

5. Electrical Power Subsystem—IntroFunctions Lesson 19

6. Electrical Power Subsystem—IntroFunctions Lesson 19

7. Electrical Power Subsystem—IntroComponents—Power Source • Power Generation (solar, chemical, nuclear) • Photovoltaic (PV) Cells • Solar energy → electricity • Static power sources • Heat energy → electricity (RTGs, solar concentrators) • Dynamic power sources • Heat energy → electricity (Brayton, Stirling, Rankine cycles) • Primary batteries / fuel cells • Chemical energy → electricity • Considerations • Mission length, distance to sun, complexity, cost, … Lesson 19

8. Electrical Power Subsystem—IntroComponents—Power Source From Space Vehicle Design, by Griffin and French Lesson 19

9. Electrical Power Subsystem—IntroComponents—Power Source Lesson 19

10. Electrical Power Subsystem—IntroComponents—Power Source Lesson 19

11. Electrical Power Subsystem—IntroComponents—Energy Storage • Power Storage • Secondary batteries • Electricity chemical energy • Other theoretical possibilities • Electricity  heat energy (parafins, salts) • Electricity  mechanical energy (flywheel) • Electricity  EM energy (microwave, lasers) • Electricity  mass (whoah!) • Considerations • Secondary batteries: DoD, # lifetime cycles • General: efficiency of conversion Lesson 19

12. Electrical Power Subsystem—IntroComponents—Power Distribution • Moves power around the satellite: • From solar arrays to loads • From solar arrays to batteries • From batteries to loads • Ohm’s law tradeoff • V=IR • P=I2R • We must keep current low to keep wire size down, implies higher voltages which required more insulation, which then becomes a safety issue (exactly the same problem for any power grid) Lesson 19

13. Electrical Power Subsystem—IntroComponents—Power Distribution Lesson 19

14. Electrical Power Subsystem—IntroComponents—Power Distribution Lesson 19

15. Electrical Power Subsystem—IntroComponents—Power Regulation & Control • Prepares power for use by payload and subsystems • Maintain constant voltage despite demand! • Convert to different voltages (± 28 VDC, ± 5 VDC, …) • Overhead required • Limit current / fuses for ground testing • Shunt excess power • Circuit breakers • Must decided between peak power tracking and direct energy transfer • Efficiency vs. complexity • Manual vs. automatic Lesson 19

16. Electrical Power Subsystem—IntroComponents—Power Regulation & Control Also see Fig 11-13 in SMAD From Spacecraft Systems Engineering, by Fortescue and Stark Lesson 19

17. Electrical Power Subsystem—IntroComponents—Power Regulation & Control • Spacecraft startup issues: • Separation switches • Current in the loop or switching? • Safety vs. Reliability (FS-2 uses 5 in series!) • Permanent latches? • Minimum power startup requirements • Battery charge level, lighting conditions, etc. Lesson 19

18. Electrical Power Subsystem—IntroComponents—Power Regulation & Control Lesson 19

19. Electrical Power Subsystem—IntroFalconSAT-3 EPS Lesson 19

20. Electrical Power Subsystem—IntroFalconSAT-3 EPS • Functional Requirements • Produce, store, condition and distribute power to payloads and subsystems • Detailed Requirements • 9.4 The SV shall use the Spacequest EPS Module • 9.4.3.2 - .3 Regulated power line--the power module shall provide a regulated +4.6V power line and a regulated +3.3V power line. • 9.4.3.4 Unregulated power line--the power module shall provide a single unregulated raw battery line. • 9.4.4 Solar Panel Inputs--the power module shall be limited to a total of 4 solar panel inputs, each to its own Battery Charge Regulator (BCR) with a total wattage capacity of 30 watts. • 9.3 The SV shall use NiCd Cells in a Spacequest tray • 9.3.5 Battery Cells--the battery shall consist of 7 Sanyo R Series N-4000 DRL D-size NiCD cells with capacity of 4300 mA-hr. • 9.14.5 The SV shall use multi-junction GaAs Solar Panels • 1.2.2 The SV shall be deployed into an orbit with the following elements: altitude 560 km eccentricity TBD (near circular), inclination of 35 deg, RAAN TBD. • Payload and Subsystem power requirements—Found in FalconSAT-3 PDR Requirements Validation Report Lesson 19

21. Electrical Power Subsystem—IntroFalconSAT-3 EPS • Solar Arrays • 4, 20 watt Spacequest GaAs solar arrays • Battery • 7 Sanyo R Series N-4000DRL D size cells in series • fast-charge series • capacity = 4300 mAh • voltage = 1.2 – 1.4 V per cell / 8.4 – 9.8 V total • Power Distribution • 2 regulated lines, 1 unregulated line • # of switches – 13 Lesson 19

22. TX Power Distribution BCR BCR ADC ADC BAT Solar Panels Electrical Power Subsystem—IntroFalconSAT-3 EPS Lesson 19

23. Electrical Power Subsystem—IntroFalconSAT-3 EPS Lesson 19