USAFA Department of Astronautics I n t e g r i t y - S e r v i c e - E x c e l l e n c e Astro 331 Electrical Power Subsystem—Intro Lesson 19 Spring 2005

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 2 Electrical Power Subsystem—Intro Objectives 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

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 3 Electrical Power Subsystem—Intro Driving Requirements

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 4 Electrical Power Subsystem—Intro Functions 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)

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 5 Electrical Power Subsystem—Intro Functions

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 6 Electrical Power Subsystem—Intro Functions

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 7 Electrical Power Subsystem—Intro Components—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, …

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 8 Electrical Power Subsystem—Intro Components—Power Source From Space Vehicle Design, by Griffin and French

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson 19 9 Electrical Power Subsystem—Intro Components—Power Source

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—Power Source

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—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

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—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=I 2 R 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)

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—Power Distribution

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—Power Distribution

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—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

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—Power Regulation & Control From Spacecraft Systems Engineering, by Fortescue and Stark Also see Fig in SMAD

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—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.

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro Components—Power Regulation & Control

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro FalconSAT-3 EPS

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro FalconSAT-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 o Regulated power line--the power module shall provide a regulated +4.6V power line and a regulated +3.3V power line. o Unregulated power line--the power module shall provide a single unregulated raw battery line. o 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 o Battery Cells--the battery shall consist of 7 Sanyo R Series N-4000 DRL D-size NiCD cells with capacity of 4300 mA-hr The SV shall use multi-junction GaAs Solar Panels 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

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro FalconSAT-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

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro FalconSAT-3 EPS Solar Panels BCR BAT ADC BCR ADC TX Power Distribution

I n t e g r i t y - S e r v i c e - E x c e l l e n c e 3 Jan 05Lesson Electrical Power Subsystem—Intro FalconSAT-3 EPS