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 331Electrical Power Subsystem—Intro

Lesson 19

Spring 2005

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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

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Electrical Power Subsystem—IntroDriving Requirements

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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)

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Electrical Power Subsystem—Intro

Functions

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Electrical Power Subsystem—IntroFunctions

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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, …

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Electrical Power Subsystem—Intro

Components—Power Source

From Space Vehicle Design, by Griffin and French

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Electrical Power Subsystem—Intro

Components—Power Source

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Electrical Power Subsystem—Intro

Components—Power Source

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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

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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=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)

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Electrical Power Subsystem—Intro

Components—Power Distribution

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Electrical Power Subsystem—Intro

Components—Power Distribution

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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

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Electrical Power Subsystem—Intro Components—Power Regulation & Control

From Spacecraft Systems Engineering, by Fortescue and Stark

Also see Fig 11-13 in SMAD

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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.

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Electrical Power Subsystem—Intro Components—Power Regulation & Control

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Electrical Power Subsystem—IntroFalconSAT-3 EPS

IFC

TX

Solar Panels

S-Band Patch Antennas

BCRTelemetry

MPACS

RX

BAT

AIM

Y Torque Rod

PIM

RPA-ARPA-A

RPA-BRPA-B

SunSensors

S-Band Omni Top

S-Band Omni Bottom

UHF WhipOmni

Antennas

FalconSAT-3 Component Placement

Telemetry

UHF Tx

RX BufferAmps

RX BufferAmps

TorquerElectronics

A/D Telemetry Board

Splitter

VHF RX

UHF RX

ADC

GGBoom

GGBoom

MPACS

Z Torque RodZ Torque Rod

FLAPSFLAPS

PLANEInterface Board

USAFAControlBoard

MagnetometerMagnetometer

PIMFLAPSMDACS (4)Torquer ElectronicsMagnetometerUSAFA Cntl BoardADC TelemetryBoom Trickle

USAFA Built

New Design

COTS11 22 33 44 55 66 77

UHFVHF

X Torque Rod

S-BandTx Power

Distribution

TX AntennaSwitch

IFC-1000 Computer & Modems

BCR

LightBand

Sep sw and charge

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Electrical Power Subsystem—IntroFalconSAT-3 EPS

Functional RequirementsProduce, store, condition and distribute power to payloads and subsystems

Detailed Requirements9.4 The SV shall use the Spacequest EPS Module

o9.4.3.2 - .3 Regulated power line--the power module shall provide a regulated +4.6V power line and a regulated +3.3V power line.

o9.4.3.4 Unregulated power line--the power module shall provide a single unregulated raw battery line.

o9.4.4 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 o9.3.5 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

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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

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Electrical Power Subsystem—IntroFalconSAT-3 EPS

Solar Panels

BCR

BAT

ADCBCR ADC

TX

PowerDistribution

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Electrical Power Subsystem—IntroFalconSAT-3 EPS