Module J
Trade Study Process
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Trade Study Objectives
• Support the decision needs of the system
engineering process
• Evaluate alternatives (requirements, functions,
configurations)
• Integrate and balance all considerations (cost,
performance, producibility, testibiity,compatibility,
supportability, etc)
• Develop and refine a system concept
• Determines if additional analysis, synthesis, or
trade-off studies are required to make a selection
Trade studies support selection of the
best or most balanced solution
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Purposes of Trade Study
• Trade studies - General
– Identify and execute trade-offs among requirements, design, schedule, and cost
– Support decision needs of system engineering process
– Level of study commensurate with cost, schedule, performance, and risk impact
• Requirements analysis trade studies
– Establish alternative performance and functional requirements
– Resolve conflicts between requirements
• Functional analysis/allocation trade studies
– Support functional analysis and allocation
– Determine preferred set of requirements for function interface
– Determine requirements for lower-level functions
– Evaluate alternative architectures
• Synthesis trade studies
– Establish system/CI configurations
– Assist in selecting system concepts and design
– Select HW/SW, make or by, examined proposal changes, etc.
• System/cost effectiveness analysis
– Develop MOEs hierarchy
– Identify critical MOEs as TPMs
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Trade Study Guidelines
• Boeing Systems Engineering Manual
–
–
–
–
Disciplined process
Fair and consistent evaluations
All affected aspects of program participate
Trade study leader to help focus and coordinate
Best
balanced
solution
• DSMC Systems Engineering Fundamentals
– Formal decision analysis method
– Solve complex problems with more than one
selection criterion
– Provide documented decision rationale
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Integrate and
balance all
requirements
Value of Trade Study Process
• Systemization of thought
• Clarification of options, problem structure, and
available trade-offs
• Improved communication of ideas and professional
judgement within the organization
• Improved communication of rationale for action to
others outside the organization
• Confidence that all available information has been
accounted for in a decision
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Trade Study Functions in Each
Acquisition Phase
Acquisition phase
Trade study emphasis
Pre-Concept Exploration
• Compare alternative sets of requirements to see how
they meet general customer needs
• Compare technologies and approaches
• Evaluate concepts for meeting mission needs
• Select alternate system configurations
• Select preferred technologies
• Reduce alternatives to a testable number
• Select component/part designs
• Select testing methods
• Select support processes
• Examine advantages of proposed design changes
• Evaluate new mission requirements
• Assess incorporation of new technologies
Concept Exploration
and Definition
Program Definition
& Risk Reduction
Engineering &
Manufacturing
Development
Production &
Deployment
Trade study emphasis areas change
throughout the acquisition process
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Trade Study Process Key Elements
Define the
problem
Establish
evaluation
criteria
Quantify downselected
alternatives
– Performance
– Weight
– Reliability
– Producibility
– Safety
– Etc
Develop
alternative
solutions
Order alternatives
relative to criteria
Screen
alternatives
Prepare Trade
Study Report
Scope of application of any one step will vary
depending on a program’s current acquisition phase
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Trade Study Process Flow
Define objectives
and requirements
Formulate
evaluation criteria
Identify alternative
Select configurations
Weigh the
criteria
Quantify
evaluation criteria
Prepare utility
functions*
Evaluate
alternatives
Perform
sensitivity checks
* Software tool is available
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Execute
decisions
Develop costing
functions
QFD Identifies and Supports Trade Studies
• The correlation matrix identifies the
relationship between the HOWs
Correlation Matrix
HOW vs HOW
Strong positive
Positive
No relation
Negative
Strong negative
IPTs identify the conflicts or synergies between
each of the HOWs in the roof of the house of quality
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Establishment of Effective
Evaluation Criteria
•
•
•
•
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Must reflect all technical requirements
Must reflect business objectives
Must be closely linked to TPMs
Effective screening/evaluation criteria must:
– Differentiate meaningfully between alternatives without bias
– Relate directly to the purpose of the trade study, i.e., they are
requirements based
– Be broadly based to ensure coverage of all decision factors
– Be independent of each other to the greatest degree possible
– Be universally understood by all trade study participants
Example of Evaluation Criteria
• Life Cycle Cost
• Supportability
• Performance
Formulate
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
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Weight
Power
Accuracy
Size
Cost
Schedule
Risk
Testability
Supportability
Complexity
Reliability
Maintainability
Safety
Quantify
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
Weight = 565 lb
Power = 32 kW
Accuracy = 2 m
Size = 2 ft3
Cost = $1.2M
Schedule = 3.5 yr
Risk = Medium
Testability = 99% FD/FI
Supportability = 3 tools
Complexity = Medium
Reliability = 500 hr MTBF
Maintainability = 0.5 MMH/FH
Safety = 99.999%
Sources of Design Trade Study Decision Criteria
Business Objectives
Mission Area Analysis
Concept Exploration
Program Definition
& Risk Reduction
Engineering &
Manufacturing
Development
Production & Deployment
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•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Program management business plan
Service mission roles
Mission area plans (MAPS)
Voice of the customer
Justification for major system new start -Mission Need
Statement (MNS)
System performance requirements
Acquisition decision memorandum
Operational requirements Document (ORD)
System specification
Test and evaluation master plan
Technical Performance Measurements (TPMs)
Planning, programming, and budgeting system documentation
Configuration Item Specifications (CIS)
Requirements Allocation Document (RADs)
TPMs
Integrated program Summary
Planning, programming, and budgeting system documentation
Existing technical manuals
Logistics plan
Production plan
Fielding plan
Identification of Alternatives
• Reflect widest range of different solutions
• Sources include:
– Predetermined, competitive bids
– Developed
•
•
•
•
•
•
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Customer
Synthesis
Brainstorming, all disciplines
QFD
Experience
Suppliers
Identification of Alternatives
Maximum limit
of affordability
Cost
Most tradeoffs
occur in this region
where decisions
are difficult
Minimum
acceptable
effectiveness
Cost
target
(goal)
Effectiveness
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Effectiveness
goal
Screen Alternatives
• Eliminate alternatives which do not appear to meet
requirements (go/no-go tests or killer trades)
• Eliminate alternatives with low probability of
successful implementation
• Eliminate alternatives which are expected to exceed
cost and schedule constraints
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Example of Uncoupling and Killer Trades
• Evaluate and select propulsion subsystem for long
range conventional cruise missile
System Req’ts: • Range 2,000 NM
• Launcher-ship VLS, be compatible and maintain
commonality
• All other requirements held constant (e.g. lethality)
SOW Task:
Propulsion subsystem
Turbojet
Type
Turbofan
Propfan
Subsonic
Speed
Altitude
Rocket Ramjet Rocket Scramjet
Supersonic
Hypersonic...
Low
High
Low
High
Low
High
High
High
High
High
Range, NM
1,200
1,600
1,600
2,000
2,100
2,600
500
800
200
300
Meets reqt
No
No
No
Yes
Yes
Yes
No
No
No
No
• Uncoupling allowed looking at propulsion subsystem only
• Killer trade reduced concepts from 10 down to 3 for more
detailed analysis
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Quantify Downselected Alternatives
• Performance
• Weight
• Reliability
• Producibility
• Safety
• Affordability
• Schedule
• Risk
• Etc
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Sample Criteria Weighting
Mission
capability
0.16
Speed &
endurance
0.09
0.33
Cargo
capacity
Logistics/
R&M
0.05
Speed at
max power
0.11
Endurance
at 27 kts
0.24
Safety
0.09
Max tank
condition
0.17
No. of
tanks
No. of
vehicles
0.02
No. of
containers
0.36
Cargo
capability
0.27
Max helo
condition
0.05
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0.06
Pierside
0.06
No. of
helos
0.02
No. of
vehicles
0.01
No. of
containers
0.09
In-stream
Sample Prioritization Input Sheet
SL-7 CLASS CONVERSION TRADE-OFF STUDIES
PRIORITIZATION SURVEY
WHAT IS YOUR OPINION AS TO WHICH MISSION
CAPABILITY ATTRIBUTE IS MORE IMPORTANT
TO MISSION SUCCESS?
MISSION ATTRIBUTE
MISSION ATTRIBUTE
CARGO CAPACITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
CARGO CAPACITY
CARGO CAPACITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SPEED & ENDURANCE
CARGO CAPACITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
LOGISTICS/R&M
CARGO CAPACITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SAFETY
CARGO CAPABILITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SPEED & ENDURANCE
CARGO CAPABILITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
LOGISTICS/R&M
CARGO CAPABILITY
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SAFETY
SPEED & ENDURANCE
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SPEED & ENDURANCE
SPEED & ENDURANCE
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SAFETY
LOGISTICS/R&M
9–8–7–6–5–4–3–2–1–2–3–4–5–6–7–8–9
SAFETY
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Sample Multi-Attribute System
Effectiveness Model
100
System
30
20
Life cycle
cost
Schedule
15
Demo
10
IOC
5
RDT & E
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FOC
Performance
15
MTBF
5
O&M
30
Availability
5
10
Prod
20
10
CEP
5
MTTR
10
Lethality
5
Range
5
Response
time
Sample Utility Curves
10
8
6
Score 4
2
0
1000
500
MTBF (hr)
0
0
0.5 1.0 1.5
Air alignment time (hr)
98
99
IOC
10
8
6
Score 4
2
0
0.5 1.0 1.5 2.0 2.5 3.0 Max
0
In-flight accuracy
Nuclear hardness
(CEP drift rate, NM/hr)
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97
98
1st prod del
00
Sample Weighted Summary Table
Alternatives
Criteria
[weight]
Alternative 1
Alternative 2
Alternative 3
Alternative 4
Alternative 5
Score
Weighted
score
Score
Weighted
score
Score
Weighted
score
Score
Weighted
score
Score
Weighted
score
A [15]
3.1-3.5
46.5-52.5
4.2-5.9
63.0-88.5
6.0-6.5
90.0-97.5
3.5-5.2
52.5-78.0
4.5-5.0
60.0-82.5
B [20]
3.9-4.6
78.0-92.0
7.8-8.2 156.0-164.0 8.9-9.2 178.0-184.0 6.4-6.9 128.0-138.0 7.6-8.1 152.0-162.0
C [10]
5.2-6.0
52.0-60.0
4.3-6.0
D [35]
9.0-9.5 315.0-332.5 7.0-7.3 245.0-255.5 8.5-9.0 297.5-315.0 9.7-9.9 339.5-346.5 6.7-7.2 234.5-252.0
E [20]
5.0-6.7 100.0-134.0 3.5-4.5
70.0-90.0
Total
591.5-671.0
577.0-658.0
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43.0-60.0
7.0-8.2
70.0-82.0
7.3-8.5
73.0-85.0
9.2-9.5
92.0-95.0
5.0-6.0 100.0-120.0 6.9-7.2 138.0-144.0 7.8-8.2 156.0-164.0
735.5-798.5
731.0-791.5
694.5-755.5
Trade Study Report
Ref Boeing Systems Engineering Process Manual
1. Introduction
– Problem description
– Ground rules/assumptions
– Constraints
2. Concepts
– Range of options
– Procedure used
– Drawings/data sheets
3. Downselected alternatives
– Screening/downselection
process
– Evaluation criteria
– Weighting factors
– Results of screening
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4. Quantified technical impact
– Detailed studies
– Additional assumptions
– Additional analysis
5. Conclusions and
recommendations
– Reasoning
– Additional recommendations
Trade Study Product Characteristics
In order to meet customer quality requirements, each Trade Study
conducted within Product Definition is expected to be characterized
by a consistent set of elements which include . . .
• Clear problem statement
• Identification of requirements that must be achieved
• Ground rules and assumptions
• Decision criteria
• Resource requirements statement (source/man hrs reqd)
• Schedule to accomplish (proposed and actual)
• Potential solutions and screening matrix
• Comprehensive array of feasible alternatives
• Comparisons of alternatives using decision criteria
• Technical recommendation of trade study leader
• Documentation of decisions leading to recommendation
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Why Do Trade Studies?
Have all the alternatives been considered?
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The Name of the Game - Trade-Offs
Performance
requirements
Technical
parameters
Producibility
Cost
Reliability
Schedule
Maintainability
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