Reliability of Spacecraft Power Systems
Transcript of Reliability of Spacecraft Power Systems
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Thales Alenia Space ETCA
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Reliability of Spacecraft
Power Systems
Fabrice WALLECAN(March 2011)
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Agenda
Part 1: Introduction
1. The space environment 2. Overview of Spacecraft Power Electronic systems
3. Reliability basic theory
Part 2: Reliability Improvement Methods
1. Actions on components
2. Product Assurance as a guarantee of Quality
3. Actions on Environment
4. Actions on Electronic Design
CONCLUSIONS
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Part 1: Introduction
1. The space environment 2. Overview of Spacecraft Power Electronic systems
3. Reliability basic theory
Part 2: Reliability Improvement Methods
1. Actions on components
2. Product Assurance as a guarantee of Quality
3. Actions on Environment
4. Actions on Electronic Design
CONCLUSIONS
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Severity of Space Environment
Some examples:
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Severity of Space Environment
And also:
The main ones at reliability point of view are:
Radiations: multiple impacts on Solar Arrays and semi-conductors; they
generate atomic oxygen in LEO; accumulation of electrical charges in
insulating materials creates ESD (and probably induced EMI); Temperature: impacts on wearing out; drift of performances, increase
of mechanical stress;
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Satellite Systems Overview
A satellite is made of
P/F (Platform) Mechanical & thermal structure
Electrical system, avionic, propulsion
On-board computer, software, remote control
Energy sources: solar, batteries, fuel
P/L (Payload)
Antennas, TWTA,
Camera, altimeter, radar, detectors,
Clock, scientific instruments,
P/F P/L
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P/FEquipments
Power Supply Subsystem Architecture of Satellites (Bus Generation: Primary Power)
~80 cm
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Conditioning architecture: PCDU and Interfaces Regulated bus
Voltage variation is limited to about +/- 1 V whateverthe satellite modes
Need of dedicated electronics to manage the batterydischarge Substantial power dissipation inside the PCDU during
eclipse phase
Unregulated bus
Bus voltage is imposed by the battery voltage
Impact on all DC/DC converters efficiency Semi-regulated bus Regulated bus in sunlight only (No more used today)
Choice is based on
Users need (mission) Scientific payloads may require regulated bus to fulfill
their precisions Variability of power load (e.g. telecom Pmin to Pmax) Thermal stability of some specific loads may requires
regulated bus (thermal management is easier in thatarchitecture)
Users flight heritage
Example ofP/FEquipments
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Power Supply Subsystem Architecture of Satellites (Bus Users Secondary Power)
P/L Equipments
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DC to DC Converter: Forward Active Clamp Topology
C1D1 D2
C2D3 D4
C3
N5V
P5V
3V5
7V6C4
M1 D10
D11
D12
X1
X2
X3
X4
D14C6
M2
X5
C7
U1
U2
R15
R16
4V2
Telemetry
PWRBUS
X6
X7
Vref_sec
C8D15
D16
SECONDARY
GND
PRIMARY
GND
en
en
enLDO1
LDO2
LDO3
Drivers
INPUT FILTER& PROTECTIONS
FLIP
FLOP
CONTROLLER
START-UP &
PROTECTIONS
CLK
OUTPUT TIMING
CONTROL
Vaux_sec
Voltage regulation
Bootstrap voltage
Example ofP/L Equipments
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Definitions according to
is the ability of an item to be in a state to perform a required function
under given conditions at a given instant of time or over a given timeinterval, assuming that the required external resources are provided
is a collective term used to describe the availability performance andits influencing factors: reliability performance, maintainability
performance and maintenance support performance
is the ability of an item to perform a required function under given
conditions for a given time interval
is the system state where an acceptable level of risk with respect to
- fatality, injury, damage to hardware, damage to manned flight system,
pollution of the environment, damage to public or private property -is notexceeded
is the ability of an item under given conditions of use, to be retained in, or
restored to, a state in which it can perform a required function, when
maintenance is performed under given conditions and using stated
procedures and resources
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Availability and Reliability
The system effectiveness and success depend on its availability for theintended use
The availability has two components:
Reliability
Maintainability
For satellites once launched, the availability only depends on the reliability
Reliability is based on the probability of numerous components workingtogether successfully over the entire mission duration
The probability of failure of a component comes from:
Random failure
Wear-out failure
Design failure
Manufacturing failure
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The general expression of reliability isknown as the Poisson distributionfunction (exponential function of time) :
Reliability R(t)
Unreliability U(t)
Reliability Expressions
Series configuration:
Parallel configuration:
t
etR
=
)(
)(1)( tRtU =
=
=n
i
RiRs1
=
=n
i
RiRp1
)1(1
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Failure Rate Estimation
Reliability models of components:
Various model of the failure rate were proposed through standards and handbooks
(ref.: MIL-HDBK-217, RDF2000, UTE80810, )
For example, in MIL-HDBK-217, the basic model is :
= b.T. S. E. A. Q. n
Basic failure rateaccording to tests
Coef. Function ofthe temperature
Coef. Function of
constraints (stress)
Environmental Coefficient taking intoaccount the particular environment thecomponent is going to be used
Adjustment Coefficient taking into
account secondary and particularuse constraints
Quality Coefficient taking intoaccount the quality level thecomponent was designed with
Adjustment Coefficientof other factors (nbr of
cycles,)
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Example of Failure Rate estimation for diodes
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Part 1: Introduction
1. The space environment
2. Overview of Spacecraft Power Electronic systems
3. Reliability basic theory
Part 2: Reliability Improvement Methods
1. Actions on components
2. Product Assurance as a guarantee of Quality
3. Actions on Environment
4. Actions on Electronic Design
CONCLUSIONS
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Reliability Improvement Methods
What to do for improving Reliability of Hardware systems
or equipments?
Parts management Selection of components
Reliable circuit Design Analyses
Environmental Design Electronic circuits Hardening
Fault tolerant Design Redundancies
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Parts Management
The main key elements for an effective Parts Management:
Use of Preferred Parts List (PPL):
In the course of a design effort, equipment designers need to select the parts and materials to be
used to meet specified equipment requirements for performance, reliability, quality, reproducibilityand cost. This selection task is greatly enhanced if the designer has a list of preferred partsavailable to help in this selection process.
Vendor, Technology and Device Selection:
It is imperative that engineers select and use components from manufacturers in which they haveconfidence. This confidence can be attained either empirically through adequate pastperformance of the part manufacturer, or from verification that the manufacturer is indeedproducing high quality parts.
Design for Manufacturability:
The best part used in a good design is useless, unless it can be processed in a reliable andreproducible manner.
Example of mounting method for a discrete part:
What to do for improving Reliability of Hardware systems ? Parts management Selection of components Reliable circuit Design Analyses Environmental Design Electronic circuits Hardening Fault tolerant Design Redundancies
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2) FMECA : Failure Mode Effect and Criticality Analysis:
On the basis of a functional description and analysis, of thedesign and considering the various modes of failure of the
components, the designer reviews the effects a componentfailure may have on the relevant function as well as itsconsequences on the complete equipment.
The ultimate goal is to check that the delivered equipment isimplemented in such way that:
The design fully respects its specifications (protections,limits, )
There is no SPF (Single Point Failure or total loss afterone failure)
No propagation of a failure may happen
Reliability Engineering Analyses - FMECA
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3) The WCA: Worst case Analysis
Its aim is to check that the design will continue to operate in its specifications during all the
lifespan of the material, taking into account : the initial tolerance of the components parameters,
the drifts in temperature
the degradations due to ageing
The radiations (cumulated dose).
This analysis is completed by the designer, using
Extensive and modelling of the design.
Specific component databases showing parameters affected by temperature; time andflying conditions
Reliability Engineering Analyses - WCA
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3) The WCA: Worst case Analysis (contd)
The Worst case analysis performed thanks to a mathematical formula linking the analysed parameter to all the other influencing parameters,
rigorously determining the variation range of the analysed parameter, considering
the simultaneous existence of the environmental conditions (T, radiation, ),
Extreme conditions of operation
Extreme variations of other parameters (power supply voltage, ).
Three approaches of calculation are considered :
The linear approach (EVA Extreme Value Analysis)
The RSS approach (Root Square Sum) The Monte-Carlo approach (Statistic)
Reliability Engineering Analyses - WCA
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Environmental Design
Most important Environments that influence the electronic design:
Radiations: multiple impacts on Solar Arrays and semi-conductors; they generate atomic
oxygen in LEO; accumulation of electrical charges in insulating materials creates ESD(and probably induced EMI);
Thermal: temperature effect has impacts on wearing out; drift of performances, increaseof mechanical stress;
ESD / EMC: impacts on availability (system malfunctions), power quality, lifetime,
What to do for improving Reliability of Hardware systems ? Parts management Selection of components Reliable circuit Design Analyses Environmental Design Electronic circuits Hardening Fault tolerant Design Redundancies
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Radiations andSEP
Environmental constraints: Radiation Sources
Trapped electrons
Van Allen belts
Trapped protons
Van Allen belts
Solar protons
Sun eruptions
Space heavy ionsCosmic rays
=> The radiation environment has a direct impact on the definition & sizing of EPS
EffectsEffects
Total doseTotal doseDecreasing of semi-conductorperformances up to destruction
SA cells, Mosfets, Bi-polartransistors,
S.E.E.S.E.E.Transient effect on semi-conductors,
may lead to its destructionMosfets, Memory, Amplifiers,
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Radiations andSEP
The hardening of hardware devices to Radiations:
Use of Rad-Hard and SEE free components:
They are greatly differ from standard components used in conventional industry:
The semiconductor manufacturing process is specific The price is very much higher
(2 for a industry standard Mosfet against 380 for a Rad-Hard one)
Use of local shields to lower the total dose:
Thickness of shields depend on direction and strength of radiation sources
Place the component at another physical location inside the equipment Use of hot redundancies of functions or low pass filters to improve immunity to SEE:
Example for a D-Flip-Flop:
By negotiating the specifications
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Thermal Design
The thermal environment and electronic design
Main Reliability improvement solution: COOLING !
Actions on packaging:
Dissipative components are mounted close to the equipment baseplate
Use of FEM tools for the design and to support the reliability engineering analyses:
Actions on materials selection: Use of metallic enclosures that provide a low thermal impedance, high mechanical stiffness and
good ESD/EMC shielding effectiveness
Use of high copper density multi layers PCBs that improve the thermal path to the mechanicalstructure
R di i d ESD
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Radiations andESD
ESD sources
on Ground
Theireffects
R di ti d ESD
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Radiations andESD
ESD sources
In Flight
Induced
effects
Accumulation of
electrical charges(Spacecraft charging)
Final
effects
Power system effects
Equipment failure
Power quality degradation
Electrical malfunctions
Untimely equipment switch-off
ESD on EURECA SAsresulting from
spacecraft charging
ESD Miti ti t h i
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ESDMitigation techniques
At component level On ground In flight
Avoid metallic floating parts
Use of appropriate filtering
Use of shielded harness
Etc
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Fault Tolerant Design
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Fault Tolerant Design
Active or Hot redundancy:
The redundant device is able to operate immediately after a failure without requesting any
external action
SeriesRedundancy
ParallelRedundancy
Series-ParallelRedundancy
BimodalSeries-ParallelRedundancy
BimodalParallel-Series
Redundancy(Cross strapping)
Fault Tolerant Design
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Fault Tolerant Design
Standby or Cold redundancy:
The redundant device is not able to operate immediately after a failure and requests
external action(s)
Fault Tolerant Design
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Fault Tolerant Design
Voting techniques (= Active redundancy): Minority / Majority voting
The Valid decisions are made only if the number of useful elements exceeds the failed
elements
Application example for a single electrical signal (PCU Main bus voltage Error Amplifier) :
PCB routing isalso performedwith redundant
tracks!
TMTC N
MEA Channel1
F540_1
VBUS_MEA
ReferenceVoltage1
MEA
ST_MEA_1
REF_10_0
Regulation1F540_2
F540_3
VBUS_MEA
ReferenceVoltage2
ST_MEA_2
REF_10_1
Regulation2F540_4
VBUS_MEA
TP_MEA_IN_1
TP_MEA_IN_2 TP_MEA_OUT
TM_MEA
MEA Channel2
1/2 voter
MEA Channel1
F540_1
VBUS_MEA
ReferenceVoltage1
MEA
ST_MEA_1
REF_10_0
Regulation1F540_2
F540_3
VBUS_MEA
ReferenceVoltage2
ST_MEA_2
REF_10_1
Regulation 2F540_4
VBUS_MEA
TP_MEA_IN_1
TP_MEA_IN_2TP_MEA_OUT
TM_MEA
MEA Channel2
1/2 voter
GND_MEA GND_MEA
TMTC R
F540_5 F540_5
[ ])4,3min(),2,1min( meameameameaMAXVMEA =
Fault Tolerant Design Various examples
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Fault Tolerant Design Various examples
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Conclusions
Increasing reliability of electronic hardware is a long iterative process ! It requests:
A lot of time during the development phases A high level of engineering knowledge (specialists in multiple disciplines are needed)
Different equipment models (Prototypes, EM, QM,) to finally get Flight Models (FM)
Reliability has a COST:
Lets take for example the cost of a triple outputs DC to DC converter (low power): Conventional market: 0.1 k Military market: 1 k
Space market: 10 k
Like in many disciplines, the rule of common sense also applies in reliability !
Improving reliability often means much more components; which induces in turnunreliability
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Thank you for your attention
Questions ?
Comments ?