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What is Systems Engineering? & What Does a Systems Engineer Do???
Guest Lecturefor Senior Design class
Howard University
by
Jeffrey VolosinNASA
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Engineering
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System
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Defining “System”
Spacecraft
Control Center Launch/Servicing Vehicle
Science Institute Flight Dynamics
Communication Network
Tracking Network
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Systems Engineering
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Thomas EdisonInvention Factory
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Skunkworks
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The Systems Engineering ‘Vee’Decomposition – then - Integration
Mission Requirements & Priorities
System Demonstration & Validation
Develop SystemRequirements &
System Architecture
Allocate PerformanceSpecs & Build
Verification Plan
Design Components
Integrate System &Verify
Performance Specs
Component Integration &Verification
VerifyComponent Performance
Fabricate, Assemble, Code &
Procure Parts
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NASA Systems Engineering Timeline
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Space Shuttle
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Mars Rover 2020
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Transiting Exoplanet Survey Satellite
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Formulation Phase InvestmentCritical to Managing Cost
Total Program Overrun32 NASA Programs
R2 = 0.5206
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20
Definition Percent of Total Estimate
Prog
ram
Ove
rrun
Definition $Definition Percent = ---------------------------------- Target + Definition$
Actual + Definition$Program Overrun = ---------------------------------- Target + Definition$
GRO76OMV
GALL
IRAS
TDRSS
HST
TETH
LAND76
MARS
MAG
GOES I-MCENACT
CHA.REC.
SEASAT
DE
UARS
SMM
EDO
ERB77
STS
LAND78
COBE
GRO82
ERB88VOY
EUVE/EP
ULYS
PIONVEN IUE ISEE
HEAO
(Per
cent
)
Formulation
FormulationFormulation $
Formulation $
Formulation $
Formulation $Program Overrun
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Solar Dynamics Observatory
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Global Precipitation Mission
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Tropical Rainfall Measuring Mission
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Space Shuttle
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NASA Project Development Times Vary Widely
ATP-PDR = Phase A/B; PDR-CDR = Phase C; CDR-Launch = Phase D
ATP
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NASA Systems Engineering Processes
- Scope- Architecture- Requirements- Functional Decomposition- Part Selection
- Utility Curves- Robust Design
- Trade Study- Contingency & Margin- Cost Estimating- Risk Management- Technology Decisions- Trade Trees
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Scope is a definition of what
is germane to your project.
Scope DimensionsObjectivesInitiatives that implement the goal.What is the minimum that the stakeholders expect from the system for it to be successful?
NeedExplains why the project is developing this system from the stakeholders’ point of view
AssumptionsExamples:Level of technologyPartnershipsExtensibility to other missions
Schedules
Authority and ResponsibilityWho has authority for aspects of the system development?
Operational ConceptsImagine the operation of the future system and document the steps of how the end-to-end system will be used
BudgetsConstraintsExternal items that cannot be controlled and that must be met, which are identified while defining the scope
MissionDefining and restricting the missions will aid in identifying requirements
GoalsBroad, fundamental aim you expect to accomplish to fulfill need.
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Scope Example: Kepler• Need: Find terrestrial planets, especially those in the habitable zone of their stars, where
liquid water and possibly life might exist.
• Goal: Discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets
• Objective: Explore the structure and diversity of planetary systems.
• Mission or business case: Survey a large sample of stars from space
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Scope Example: KeplerOperational Concept: Use a Delta II launch vehicle to place a 0.95m telescope (capable of capturing light from 12th magnitude stars) and photometer having a field-of-view of 105 square degrees (field should include over 100,000 stars – and a sensitivity that would detect the Earth transiting the Sun from a significant distance) in an Earth-trailing solar orbit for a period of 3.5 years (allowing for measuring planet transits over multiple “years”). Point the telescope constantly at the Cygnus-Lyraregion (except when downlinking data). Downlink data through the DSN sites, with science data (downlinked monthly) going to the ARC Pipeline facility for processing and engineering data (downlinked twice each week) going to the Mission Operations Center at the University of Colorado. After processing, all data is stored at the Space Telescope Science Institute in MD.
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Scope Example: Kepler• Assumptions: There are Earth-sized
planets orbiting stars within the chosen FOV that are orbiting edge-on as seen from Earth. Also, that variations seen in the photon count from stars in the FOV can be correlated to orbiting Earth-like planets (versus star-spots or other output variations)
• Constraints: Total mass must be below 1,000 kg (to launch on Delta II to required orbit)
• Authority and Responsibility: NASA Science Mission Directorate, Astrophysics Division, Exoplanet Program Office (JPL), Kepler Project Office (ARC), Data Processing Pipeline (ARC), Mission Operations Center (University of Colorado), Data Archive (Space Telescope Institute), Launch (KSC Launch Services Program), Observatory Development (Ball Aerospace)
• Budget: $550M total funding available• Schedule: Must launch by 2009
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Architecture Example: NASA Constellation ProgramLunar Sortie Mission (2006)
Are
s I
Are
s V
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GroundLaunch Flight
Launch Pad Launch Vehicle Assembly Building
Extravehicular Support
Electrical Power
Thermal Control
Life Support
Guidance, Navigation & Control
Propulsion
Communication
Lunar Module Command Module Service Module
Docking
Radar Target Scope Drogue Window Gauge Control/Information
Mis
sion
Syst
emSe
gmen
tEl
emen
tSu
bsys
tem
Com
pone
ntPa
rtRequirements Decomposition
Example: Apollo
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Functional Decomposition ExampleNASA Space Science Mission
Functional Flow Block Diagram
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Functional Decomposition Timeline Example
Example shows the time required to perform function 3.1.Its sub-functions are presented on a bar chart showing how the timelines relate.Note: function numbers match the FFBD.
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Selecting Parts and ComponentsUtility Curves
• Use performance-resource curves (utility curves) to identify break points.• “Performance” factors should be defined by requirements and “figures of
merit”
4
3
2
1
Perfo
rman
ce
‘Cost'
A typical utility curve
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Selecting Parts and ComponentsRobust Design
• Robustness is a measure of the ability of a system to absorb changes in requirements, constraints or failures while reducing the impacts on the performance, functionality, or composition of the mission or system. Two different design options are shown - one with high performance, one with robust performance.
Util
ity
Resource or operational environment factor
Range of possible inputs
Robust Design Option
High Performance Design Option
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Trade Study Decision Matrix Example
Preferred Solution
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Contingency & Margin
Contingency
Margin
Current Best Estimate
Maximum Expected Value
Maximum Possible Value
Resource
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Contingency Adjustment by Technical Maturity
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Contingency Adjustments by Mission Phase
Parameter
Pre-Phase A Phase A Phase B Phase C
Weight 25-35% 25-35% 20-30% 15-25%Power EOL 25-35% 25-35% 15-20% 15-20%Pointing Accuracy X2 X2 X1.5 X1.5Pointing Knowledge X2 X2 X1.5 X1.5Pointing Jitter X3 X3 X2 X2Propellant 30-35% 30-35% 20-25% 10-15%Data Throughput 30-40% 30-40% 20-30% 15-25%Data Storage 40-50% 40-50% 40-50% 30-40%RF Link Margin 6 dB 6 dB 6 dB 4 dBTorque Factor X6 X6 X4 X4
Technical
Strength Factor (Ultimate) 2.1 2.1 2.1 1.75Cost (Including De-Scope Options)
25-35% 25-35% 20-30% 15-20%Programmat ic
Schedule 15% 15% 10% 10%
Project Phase
Tech
nica
lPr
og.
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CONCEPTUALDEVELOPMENT
PROJECTDEFINITION DESIGN DEVELOPMENT OPERATIONS
A B C D EPHASE
$
PARAMETRIC
DETAILED
MET
HODS
Analogies , Judgments
System Level CERs
Gen. Subsystem CERs
Calibrated Subsystem CERs
Prime ProposalDetailed
Estimates via Prime contracts / Program Assessment
• Major dip in cost as Primes propose lower
• Tendency for cost commitments to fade out as implementation starts up
As Time Goes By:• Tendency to become optimistic
• Tend to get lower level data
Cost Estimating Techniques
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Approach M - Mitigate W - Watch A - Accept R - Research
5
4
3
2
1
1
Like
lihoo
d
CONSEQUENCES
Med High
Low
Criticality L x C Trend Decreasing (Improving) Increasing (Worsening) Unchanged New Since Last Period
More flight testing may be required for Soft V&V
R DFRC-02 8
Limited Flight Envelope, due to technical issues
R DFRC-04 7
Payload Capacity & Volume Trade-offs design issues
R DFRC-11 6
Avionics software behind schedule
W DFRC-01 5
Quality Control Resources insufficient
A DFRC-24 4
Cost growth for engine components
W DFRC-07 3
Sched Integration problems structure vs.. avionics
M DFRC-12 2
Landing Gear Door System Failure
R DFRC-34 1 Risk Title
Appr oach
Risk ID
Rank & Trend
1
2
3
4 5 6
7 8
Risk Management ExampleSOFIA Project
2 3 4 5
SOFIA Risk Matrix
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Technology DecisionsHeritage vs. Advanced Technology
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ISRU NoISRU
Inte
rpla
neta
ryPr
opul
sion
(no
hybr
ids
in P
hase
1)
Mar
s Asc
ent
Prop
ella
ntM
ars C
aptu
reM
etho
dCa
rgo
Depl
oym
ent
Aerocapture Propulsive
ISRU NoISRU ISRU No
ISRU ISRU NoISRU
Aerocapture Propulsive
ISRU NoISRU
Aerocapture Propulsive
ISRU NoISRU ISRU No
ISRU ISRU NoISRU
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
NTR
Elec
tric
Chem
ical
Aerocapture Propulsive
Pre-Deploy All-up Pre-Deploy All-up
Opposition ClassShort Surface StayM
issio
nTy
pe
Human ExplorationOf Mars
Special Case1-year Round-trip
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
NTR- Nuclear Thermal RocketElectric= Solar or Nuclear Electric Propulsion
Conjunction ClassLong Surface Stay
1988 “Mars Expedition” 1989 “Mars Evolution” 1990 “90-Day Study” 1991 “Synthesis Group” 1995 “DRM 1” 1997 “DRM 3” 1998 “DRM 4” 1999 “Dual Landers” 1989 Zubrin, et.al* 1994-99 Borowski, et.al 2000 SERT (SSP) 2002 NEP Art. Gravity2001 DPT/NEXT
M1 2005 MSFC MEPTM2 2005 MSFC NTP MSA
M2M1 M1M1
M2 M2
M2 M2
Decision Package 1Long vs Short
Top-level Trade Tree-ExampleHuman Mars Mission
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