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AIAA-2009-4615
American Institute of Aeronautics and Astronautics
1
SPECTTRA: A Space Power System Modeling and
Simulation Tool
Trevor Bihl,1 John Heidenreich,2 and Douglas Allen3
Schafer Corporation, Dayton, Ohio, 45430
and
Kenneth Hunt4
Air Force Research Laboratory, Kirtland Air Force Base, New Mexico, 87117
A Satellite Power Electronic Component Technology Trades and Rapid Analysis
(SPECTTRA) tool for technology trade analysis is introduced. SPECTTRA is a Matlab
Simulink tool in the beta development stage for conceptual analysis, component sizing,
technology and system trades and payoff studies and design of experiment analysis for
spacecraft power systems. Satellite orbits are propagated for any given two line element,
permitting the analysis of load demands and electrical power subsystem behaviors for
various mission scenarios and components. Anticipated performance of theoretical or
materials, such as solar array, battery and wire materials are able to be simulated through
applying their fundamental properties to documented. Power conversion losses and
distribution losses are considered in addition to design life considerations, such as end of life
performance and degradation. SPECTTRA permits as much or as little user interaction as
desired by being operated using a graphical user interface (GUI); a user can therefore select
only which fields are of interest for a simulation. An additional GUI is used for data analysis
and plotting functions.
Nomenclature
BOL = beginning-of-life
DET = direct energy transfer
EOL = end-of-life
GUI = graphical user interface
f, g = generic functions
I-V = current-voltage relationship
I/O = input-output
LEO = low earth orbit
LOS = line of sight
PPT = peak power tracker
TLE = two line element
1 Electrical Engineer, 1430 Oak Court, Suite 303
2 Aerospace Engineer, 1430 Oak Court, Suite 303
3 Principal Engineer, 1430 Oak Court, Suite 303, AIAA Lifetime Associate Fellow
4 Group Lead, AFRL/RVSE, Space Electronics Group
7th International Energy Conversion Engineering Conference
2 - 5 August 2009, Denver, Colorado AIAA 2009-4615
Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.
The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes.
All other rights are reserved by the copyright owner.
AIAA-2009-4615
American Institute of Aeronautics and Astronautics
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I. Introduction
PACE power system design is a highly coupled process requiring knowledge of all aspects of an intended
mission. Spacecraft power system requirements are dependent on orbit parameters, power system load
demands, subsystem active/idle states, and mission requirements.1 The amount of time a satellite will be sunlit and
the mission power demands will directly influence the power architecture used, including solar array and battery
selection. Analytical preliminary design tools facilitate system development through trade analysis, sizing and cost
studies of components and technologies prior to costly outlays. SPECTTRA presents a GUI-based analytical
preliminary design tool for estimation of space power system performance through component and architecture
trades and mission simulation.
Satellite
Model
Ground
Station
Models
Environment
Models
Simulation Set-up & Monitors
Celestial
Models
Figure 1 Top Level SPECTTRA Simulation
Many design concepts that may be ignored in traditional preliminary design methods can be pursued in
SPECTTRA, such as improved system sizing through simulating active/idle load demands of a particular mission.
Analyzing system degradation and EOL performance is also supported though a satellite design life input, satellite
exponential degradation function and electrical component efficiency functions, allowing for performance
estimation throughout the design life.
Research direction can also be driven by the results of a preliminary design study, e.g. knowing expected values
for physical properties of conductors and solar panels or efficiencies of power converters allows expected benefits of
new technology to be simulated over the design life of a satellite. Results of such a study can justify further research
on a given component or material.
SPECTTRA, Fig. 1, was developed to model typical space power architecture and components. It was also
developed to be configurable, permitting satellite power preliminary design analysis such as
• design of experiment studies
• power system conceptual design
• power margin analysis
• component sizing analysis
• technology and system trade studies
• EOL performance analysis.
SPECTTRA created a space power system analysis platform by drawing extensively from the framework
developed for the Simulink-based INSIGHT parametric satellite model created at the Air Force Institute of
Technology for threat modeling and analysis.2
S
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Transients and higher order effects are not considered in SPECTTRA; component models are traceable to
component physics, but use averaged solutions with a one-hertz resolution. This permits long-term full design-life
studies to be performed by a fast running model; it was never desired to develop a high fidelity simulation due to the
levels of complexity this would entail, slower simulation times and the many, possibly fallacious, assumptions that
would necessarily be made at every level of the model. This would also render it impossible for a user to quickly
setup a simulation, estimate the power demands for the life of a satellite, change components or parameters and
create another estimate.
II. Architecture and Operation of SPECTTRA
SPECTTRA inherited and further developed the INSIGHT satellite model framework that incorporated a
coupled system of generic subsystem models found on many satellites as described in Ref. 3. Subsystem models
were developed for the Attitude Determination and Control Systems (ADCS), Telemetry Tracking and Command
(TTC), Command and Data Handling (CDH), Thermal Management, Payload and Power Regulation Systems.2 The
interconnection between satellite subsystems, ground stations for telemetry tracking, two-body orbit propagation and
mission demands is simulated; however the model did not allow for detailed power system component analysis nor
was it flexible enough to simulate different main mission payloads types and their effect on load demand.
SPECTTRA further developed this structure to model load demands of the various subsystems; active/idle
voltage states are configurable for each subsystem. The SPECTTRA payload model was developed such that many
generic mission scenarios can be simulated including its effect on power demands. The power regulation system in
SPECTTRA was developed to contain advanced and user configurable models of components, such as the solar
array, bus regulation method and load switches.
Incorporating future functionality is also being facilitated through an architecture that allows for the removal and
replacement of model components with new Simulink components that retain the required SPECTTRA data signal
format. Data important to power analysis will thereby be logged and displayable in the analysis tools. This
capability permits proprietary Simulink models to be developed and interfaced with SPECTTRA.
A. SPECTTRA GUI
SPECTTRA is interfaced through a GUI interface, Fig. 2; this was developed for system initialization, parameter
selection, and simulation running. In operation, a user would first open the GUI and then open SPECTTRA
Simulink model. A user can then either accept all present parameter values and simulation conditions (defaults or
previously saved) or make changes to any desired subsystem. A user is guided along the setup process as fields only
become accessible after a required action, e.g. parameters are not selectable prior to a model being loaded. A
conscious action is also required to permit access to parameters, forcing a user to select “Edit Subsys” to gain access
to subsystem parameters; thereby undesired changes are potentially avoided.
Figure 2 SPECTTRA Main GUI
The GUI allows a user as much or as little interaction with subsystem parameters as desired. Default parameters
are standard in SPECTTRA and a user could potentially have little interaction with the parameters or could only
AIAA-2009-4615
American Institute of Aeronautics and Astronautics
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interact with the parameters of one subsystem. The SPECTTRA GUI also has a button connecting the user to the
analysis viewer, where data from a previous simulation or the most recent run can be analyzed.
B. Power Subsystem Architecture
The SPECTTRA space power subsystem was developed to simulate various space power architectures in a
similar format as the chart in Fig. 3 describes. Currently the SPECTTRA power subsystem considers only DC
power system components. The system is designed to accommodate a user simulating a desired architecture by
selecting library blocks and GUI mask parameters.
Users can select or enter proprietary data for solar array material, solar array dimensions, DC converter
efficiencies, connecting wire materials and lengths, connector resistances, and load switch regulation parameters
among other quantities. To simulate only the desired architecture, individual library blocks are used for different
regulation techniques (presently series regulator and PPT models are available).
Subsystems are considered as loads in electrical power architectures. Active/idle voltage and current states, user
selectable for each respective subsystem, are used to compute power demand from each system. Switching from
active to idle is calculated based on mission parameters, such as lighting and targeting conditions. The total loads
demands are then used to calculate the total required power from the power system.
Power available is calculated using satellite spatial conditions from the two body orbit propagator determining
irradiance conditions of the solar array. The solar array model then estimates the power available based on the
selected solar array parameters and component physics. Load demands greater than available solar power are
augmented with the battery simulating discharging; if load demands are less than the available solar power, the
battery simulates recharging if it is needed. Excess power is simulated as being shunted.
Figure 3 Space Power Architecture
The user selected power regulation method simulates power conversion of solar array outputs to the desired bus
voltage level. The solar array calculates both the PPT point as determined through an I-V curve and the regulated I-
V values simultaneously. Selected regulation method determines which relationship is used in calculations. The
PPT model uses boost and buck DC converters to keep the main bus voltage to the desired level. Converter
inefficiencies are estimated and voltage drop to the load branches is considered. The series regulator model operates
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American Institute of Aeronautics and Astronautics
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with a constant solar array voltage and does not incorporate DC converters. Load switch models then regulate
power converted for each load voltage and current requirement and the voltage drop and losses associated with each
converter and conductor.
Sizing functions run prior to simulation aid in the initialization and reduce the likelihood that a component will
be over/under sized for the simulation. Sizing of power components takes into account expected sunlight conditions
of the satellite orbit, degradation of components and the average and maximum power demand.1 The SPECTTRA
sizing functions have been developed to simulate satellite operations for long periods of time to detect absolute
maximum power demand that will occur. A situation where the battery and solar array cannot meet load demands
would therefore not occur during normal operations. System failure modeling is not considered at this time;
however it may be incorporated in the future.
C. Data Logging
Parameters important to simulation analysis are logged in text files by a simulation monitor system, Fig. 4.
Logged parameters include:
• Sun position and conditions
• Lunar position
• Satellite ECI spatial positions and simulation time
• Battery charging logic, current, voltage, temperature, state of charge
• Payload parameters including power demand, target spatial relationship with payload, and scenario
logic parameter
• Power regulation data including power demand for all subsystems, power available, and losses
• Solar array maximum power points, open circuit voltage, closed circuit current and operating points
• Subsystem power parameters
• Masses for each subsystem.
JULIANDAY is a parameter
through the timing setup callback .
Time
1
yr2sec
3600 *24 *365
n_dateNumber
kg Monitor
yr_lifeofSat
b_logText
hblock
Timing
days _JulianDayStart
rs_Rotation
days_Jul ianDay
r_GMST
s_time
Sun Monitor
Subsystem Monitor
Solar Array Monitor
Sat Monitor Power Regulation Monitor
Payload Monitor
Moon Monitor
[satParams]
[envParams ]
[modifiedSimControl ]
[satParams]
[modifiedSimControl ]
[satParams]
[modifiedSimControl ]
[envParams ]
[modifiedSimControl ]
[envParams ]
[modifiedSimControl ]
[satParams]
[modifiedSimControl ]
[satParams]
[modifiedSimControl ]
[satParams]
[modifiedSimControl ]
[satParams]
[modifiedSimControl ]
[envParams ]
[modifiedSimControl ]
JULIANDAY
Battery Monitor
CelstialBodies
3
Environment Inputs
2
Satellite Inputs
1
s_lifeOfSat
n_dateNum ber
hblock
r_GMST Time
days_ JulianDa y
days_Jul ianDayStart
<Earth> <rs_Rotation >
b_logText
s_time
Figure 4 SPECTTRA Data Logging Subsystems
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American Institute of Aeronautics and Astronautics
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D. SPECTTRA Analysis Viewer
Data logged during the simulation is available for analysis by directly accessing the output text files or through
the dedicated SPECTTRA Viewer analysis tool, Fig. 5. This tool was also developed to analyze simulation results
through data plotting for the entire simulation or a specified time period.
The ability of the viewer extends to displaying a 3-D globe with the satellite’s orbit and ground track for either
the entire simulation or a desired time period. The time point for which data is displayed is controlled by a slider bar
at the bottom of the viewer. Instantaneous values for power system analysis are displayed bar graphs. Full
simulation time results for various power system quantities are also immediately displayed below the bar graphs; a
pull-down menu allows for the desired data to be displayed. Detailed analysis is available in the “Analysis” menu;
figures are plotted for logged data from each modeled subsystem, the payload, the power system and the solar array.
Figure 5 SPECTTRA Viewer
III. SPECTTRA Power System Component Models
The following section overviews power system component models developed in SPECTTRA. Systems such as
the ADCS, TTC and CDH are not discussed; the overall functionality of these systems is retained from IMPULSE,
however power system parameters were added or refined for the purposes of SPECTTRA. Discussions of the
payload model, power regulation and control model, solar array model, battery, and components is presented.
To facilitate material trade studies individual electrical components are modeled; this includes electrical wires,
electrical connectors and DC-DC converters. Each component is modeled using averaged solutions, i.e. transients
are not considered at this level, mass of each component is also calculated in addition to the electrical losses
incurred.
E. Main Mission Payload Model
SPECTTRA developed a main mission payload model, Fig. 6; this model considers the payload mission scenario to
calculate power demand. Power fluctuations such as those occurring when an imaging payload is activated when in
line of sight to its target are thereby simulated. The SPECTTRA payload model offers user configurable active/idle
voltage and current states and scenario conditions.
AIAA-2009-4615
American Institute of Aeronautics and Astronautics
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Payload Mission Data
2
Payload Housekeeping
1
Target Environment
Celestial Environment
r_GMST Target Environment
Power Dissipation
Payload Properties
PayloadSystemCom mand
Payload Data
Payload Failure Processing
Failure Mode Not Enabled
Payload Characteristics Subsystems
Satellite Environment
Target Environment
r_GMST
Payload Type
Payload Properties
Generic Data Processing Functions
PayloadSystemCom mand
Payload_type
Data
Mbps_Data_Rate
0
SimControl
4
CelestialEnvironmet
3
CDH
2
Env
1
Figure 6 Payload Model
To permit the simulation of many types of missions it is assumed that targeting and lighting considerations are
the primary limiting factors of most missions. This methodology provides for the realization of many mission types,
for example a laser comm. mission that is active both in day and night would is represented as a targeting mission
with no lighting consideration (active whenever the satellite is in LOS with its ground station). Similarly, a target
driven imaging mission would be considered as a targeting mission active only when the target is in daylight (or
different user selected lighting conditions).
For determining LOS conditions of the satellite to the target and the target to the sun, relative position vectors of
the satellite and sun to the target were used.5 A mask angle can also be input to simulate excluding payload activity
below a certain elevation angle over a target; for instance this could be used to simulate avoiding imaging the side of
a mountain instead of a city. Constantly active payloads are also selectable, in which case idle states, lighting and
targeting parameters are removed from the user’s selection.
F. Solar Array Model
In order for the power system architecture to accurately model the variability in the power availability, the
SPECTTRA solar array model was developed. The SPECTTRA solar array subsystem, illustrated in Fig. 7, is
modeled at the solar cell level based on the AIAA Space Power System Design Course. The IV curved for the solar
array is generated using the short circuit current density, maxim power current density, the maximum power voltage,
and open circuit voltage for a particular array material. Five materials are defined in the solar array model
including, crystalline Silicon, high efficiency crystalline Silicon, single junction GaAs, dual junction GaAs, and
triple junction GaAs. Cell current and voltage degradation due to temperature default values are also set based on the
material selection. Default parameters may be overwritten to provide the modeling of different data sets. The model
also includes several options for coverglass materials and thickness to determine the coverglass transmissivity loses
approximation. Remaining degradation terms for BOL and EOL for both current and voltage are defined by the user.
The voltage losses include block diodes, cell interconnect resistance, radiation and thermal cycling. While the
current losses include the calibration error, cell mismatching, ground handling contamination,
micrometeoroid/orbital debris, on-orbit contamination, radiation, and ultraviolet light darkening. The cell size, active
area, number of solar cell strings in parallel, and number of cells in string are defined in the configuration of the
solar array. The number of solar cell strings in parallel and number of cells in strings are defined by the sizing of the
power system. The user may also specify idealized one axis tracking or body fixed tracking to determine the cosine
loses for the sun incidence on the solar array.
AIAA-2009-4615
American Institute of Aeronautics and Astronautics
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Figure 7 Solar Array Model
G. Battery Model
The energy storage method for the SPECTTRA spacecraft model is the battery model. The battery model was
leveraged directly from the INSIGHT development. The model uses table lookups to determine the discharge and
charge rates of the NiCad, Ni H, and Lithium Ion batteries at the state of charge.
H. Power Regulation and Control Model
The SPECTTRA power regulation and control subsystem, Figure 8, contains the main bus power regulation
method (Regulated or PPT), the charging current calculator, and the battery charge/discharge regulation system.
Ancillary systems used for consistency and logic control of systems include power regulation mass calculation,
charging logic, bus voltage simulation control and max power available calculations.
Completed Mass Calculations
Corrected dissipation value .
A
_
demand
6
Mass
5
A_2BatteryTerminals
4
A_2Shunts
3
V_BusVoltage
2
PowerRegHousekeeping
1
Terminator Regulated System
Solar
Load
RegulatedBus1
Power Conversion
Dissipation
-
K-
Power Control & Conversion
Mass Calculation Calculations
Peak Power Mass
Max Power Available Calc
l_Charging
W_MaxSolarArrayAvail
V_BusVoltage
A_2BatteryTerminals
W_MaxPowerAvail
[W_ChargerLoss]
[W_PwrConv]
[V_BatteryPreConv ]
[A_BatRecharge ]
[W_maxPwrAvail ]
[W_maxPwrSolAvail ] [BattRegLoss]
[BattAmps ]
[BattVolts]
[V_BatteryPreConv ]
[BattRegLoss]
[W_PwrConv]
[A_BatRecharge ]
[W_maxPwrSolAvail ]
[W_maxPwrAvail ]
[W_ChargerLoss]
[BattAmps ]
[BattVolts]
Divide 1
Divide
W_maxPower
Charging Logic
W_Load
SolarArrayBus
l_Charging
W_ArrayPowerAfterLoad
W_maxSolarPower Avail
Charger
V_bus
A_bus
Ahr_BatteryCapacity
Ahr_BatteryState
l_Charging
W_ChargerLos s
W_2Shunts
A_Charging
Bus Voltage Switch
V_busFromPCC
l_usePCC
V_busFromBattery
Main Bus Voltage
Battery Charge /Dis charge Regulation
A_Charging
l_Charging
W_Array-Loa d
V_BatteryState
V_OverBatteryConv
A_2BatteryTerminals
W_batRegulator
V_Battery_PreCon v
Abs1
|u|
Time
4
Battery
3
SolarArray
2
Load
1
W_PCC_los ses
A_2BatteryTerminals
Battery
W_ChargerLos s
<v_outputVoltage>
<v_outputVoltage>
W_2Shunts
l_Charging
l_Charging
W_PowerConversio nLoss
W_PowerConvers ionLoss
<V_BatteryState >
<AHr_Battery_ca pacity >
Power_Housekeeping
<kg_ControlConvMass >
V_BatteryVoltsPreConv
Ahr_Battery
<Ahr_BatteryState >
<amps_outputCurrent >
A_2Shunts
A_demand
W_maxPowerAvail
W_Demand
A_BatRecharge
<W_heat>
W_PwrConvLoss
W_BattRegLoss
W_ChargerLoss
V_BatteryPreConv
Figure 8 Power Regulation and Control Model
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American Institute of Aeronautics and Astronautics
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In operation the PPT model uses DC-DC converters to control the solar array determined maximum power point
to the desired main bus voltage level. A user specified voltage margin or error is also selectable. Voltage drop from
the PPT to the bus is calculated through an electrical wire model. The output of the PPT system feeds the charger
subsystem.
If a regulated system was used instead of the PPT, the regulated outputs of the solar array would connect directly
to the main bus with no DC-DC converters. The output of the regulated system would then similarly feed the
charging system.
The charging system is controlled by the charging logic system. This system determines if it is possible to
charge the battery based on load demand and solar array outputs. It also assumes that battery charging is secondary
to subsystem operation; only in the situation where there is excess power available and the battery does not have a
full charge will the battery be recharged. The present charging system model considers two modes, trickle and
regular charging.
A battery charge/discharge regulator is fed by the charging subsystem. This system switches the battery current
between charge and discharge mode. For charging is regulated by the system described above, discharging is
regulated be a DC converter that keeps the battery discharge voltage at the main bus level.
Ancillary systems, such a the bus voltage switch system and the maximum power calculation are used to used to
monitor voltage and power parameters for data logging and consistency checking. A power regulation component
mass calculator system
is also included for
data signal logging.
I. Load
Switches/Branch
Regulators Model
The load switch
model, Fig. 9,
architecture currently
assumes to have one
branch and load
regulator for each
subsystem. DC-DC
converters are
employed to regulate
the branch voltage to
each subsystem’s
desired voltage level
and simulated the
associated losses.
Wire models are also
included in each
regulator to simulate
the voltage drop from
the regulator to the
load. Degradation of
converter efficiencies
or calculation of
converter efficiencies
based on power output
is supported. Planned
revisions to this
subsystem include
additional architecture
types that can better
represent the physical
locations of the load
Figure 9 Load Switch Model
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American Institute of Aeronautics and Astronautics
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regulators with respect to the loads and the main bus.
J. Electrical Wire Model
The electrical wire model, interface shown in Fig. 10, calculates voltage drop across a wire connecting electrical
components. The inputs are voltage and current; outputs is a bussed signal containing the voltage at the end of the
wire, current through the wire, wire length in meters, wire mass in kilograms and resistance in ohms.
Wire resistance and mass are calculated using fundamental properties of resistivity and density and applied to the
input voltage to calculate voltage drop,
IRVV inout ⋅−= , (1)
where Vout is the output voltage of the wire in volts, Vin is the input voltage in volts, R is the resistance of the wire in
ohms and I is the current flowing through the wire.6 This method of calculation also permits a user to input new
materials such as ones under development to analyze a potential technology payoff, by editing the data set of wire
materials.
The resistance of a wire is calculated as
n
A
l
R
=
ρ
, (2)
where ρ is the resistivity of the material in ohm-meters, A is the AWG-gauge cross sectional area of the wire, l is the
length of the wire in meters, and n is the number of wires.5 The default value for n is one, if a twisted set of wires is
used, n will be equal to the number of wire, with the resulting resistance considered as a parallel set of identical
wires. Wire mass is calculated as a function of density and volume (cross sectional area and wire length in this
case),
nlAM ⋅⋅= )(
κ
(3)
where, M is the mass of the wire in kilograms, κ is
the density of the material in kilograms per cubic
meter, A is the AWG-gauge cross sectional area of
the wire, and l is the length of the wire.7
Wire diameter is a user selected field from a
drop down list of AWG-gauges. AWG wire
gauges are used to accommodate using industry
standard wire diameters; it is up to the user to
know if the wire is sufficient for the modeled
application.
K. Electrical Connectors
Electrical connectors, interface in Fig. 11, such
as those used to connect a wire to a given
subsystem, are represented as a fixed user input
resistance. The voltage drop over an electrical
connector is calculated in the same manner as in
Eqn. 1.
The wide variety of connectors available and
the level of detail required to include a
representation of them makes it impossible for
SPECTTRA to include a database of connectors.
The default value of resistance for an electrical
connector is 0.0017259 ohms and the default mass
is 0.025 kilograms.
Figure
10
Electrical Wire Mask
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American Institute of Aeronautics and Astronautics
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L. DC-DC Converters
DC-DC boost (step-up) and buck (step-down)
converters are used in load switches and the PPT model to
control output voltage. DC converters typically operate
with switching frequencies from 100 Hz to 20 kHz.8 For
the purposes of SPECTTRA, which has a 1 Hz resolution,
averaged solutions were used which do not consider
voltage and current ripples and other high frequency
components.
Duty cycle for each converter is based on the desired
output voltage to the input voltage. The ratio of total input
power to total output power plus converter losses,
inlossout PPP =+ , (4)
must be accommodated. For a DC-DC buck converter the
duty cycle relationship between I/O voltages and current is
k
I
I
V
V
out
in
in
out == , (5)
where k is the duty cycle.8 For a DC-DC boost converter,
the duty cycle relationship is
kI
I
V
V
out
in
in
out
−
== 1
1
, (6)
where k is less than 1 and Vout/Vin > 1.8 Power conversion losses,
inloss P
eff
P⋅
−= 100
1, (7)
where eff represents the converter efficiency.
Converter efficiency values are determined either by a fixed user input efficiency, through an initial fixed
efficiency that degrades with the satellite similar to solar array degradation, or with a user defined 1-D lookup table
of total output power.
W_heatLoss
3
A_ out
2
V_out
1
1
100
Eff
4
A_in
3
V_Bus
2
V_in
1
A_in
W_hea t
dutyCycle
V_output
W_heatLoss
3
A_out
2
V_out
1
1
100
Eff
4
A_ in
3
V_Bus
2
V_ in
1
V_output
dutyCycle
W_hea t
A_in
Figure 12 Boost (top) and Buck (bottom) Converter Models
Figure 11: Electrical Connector Mask Interface
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IV. Simulation Data Analysis
For consideration herein, results are presented from a simulation of an example main mission imaging payload
for a LEO satellite. A target at the location of latitude 39° 10’ 45” N and longitude 82° 5’ 46” W was selected; a
targeting payload scenario was defined such that the payload would only be active when the target is sunlit and the
satellite is within LOS of the target. Data for one day of satellite operation was simulated. For the power regulation
system a PPT was selected and default parameter values were used.
Simulation data was analyzing using the SPECTTRA Viewer and figures were generated through user selection.
Payload parameters are displayed in Figure 13. This figure illustrates the functionality of the payload in the first two
graphs: the first graph displays the lighting conditions of the target (1 is sunlit, 0 is umbra), the second graph
displays satellite LOS to target (1 is within LOS, 0 is LOS not met). This targeting mission required both conditions
to be met; the results display this functionality in the bottom graph which shows spikes of payload activation only
when both conditions are met.
Figure 13 Payload Parameter Analysis
Solar array parameters for the simulation are shown in Figure 14. These graphs illustrate the solar array
parameters of maximum power points, short and open circuit points and the operating power.
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American Institute of Aeronautics and Astronautics
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Figure 14 Solar Array Analysis
Analysis of the power system architecture is displayed in Figure 15. This graph plots the total power available,
the total satellite power demand, the battery charging power and the power dissipated by shunts. The subset figure
displays data for a user selected 100 minute window of the simulated data. This figure was generated using the time
slider bar described above.
Figure 15 Analysis of Power System Architecture
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V. Conclusion
An analytic tool for space power architecture analysis and design has been presented. SPECTTRA represents a
coupled space vehicle system model that considers all major subsystems and orbit parameters. Power system
models, components and sizing tools facilitate sensitivity analysis to changes in architecture and subsystem
configuration. With payload missions simulated and load demands available for analysis for the life of a satellite,
SPECTTRA permits analyses, trade studies and parameter studies for many power system studies.
Acknowledgments
The authors would like to acknowledge the support of AFRL/RVSE, for sponsoring development of the
SPECTTRA software and NASIC/AC for developing the INSIGHT software that was used as the foundation for
SPECTTRA.
References
1
Patel, M. R., Spacecraft Power Systems, CRC Press, Boca Raton, FL, 2005.
2Bond, R. M., Caponio, D. T., Childers, L. B., et al., “Project INSIGHT: Threat Modeling and Assessment for Earth-
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