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...
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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
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 e3 Jan 05 Lesson 19 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
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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)
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 e3 Jan 05 Lesson 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 e3 Jan 05 Lesson 19 6
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
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 e3 Jan 05 Lesson 19 10
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 e3 Jan 05 Lesson 19 11
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 e3 Jan 05 Lesson 19 12
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
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 e3 Jan 05 Lesson 19 14
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
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 e3 Jan 05 Lesson 19 16
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
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 e3 Jan 05 Lesson 19 19
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
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 e3 Jan 05 Lesson 19 23
Electrical Power Subsystem—IntroFalconSAT-3 EPS