Seven Steps of Systems Engineering
(horizontal axis of Activity Matrix)
••
••
••
••
••
••
••
Problem
Problem Definition
Definition –– What
What isis the
the problem,
problem, really?
really?
Value
Value System
How will
will we
we know
know when
when we’ve
we’ve
System Design
Design –– How
found
found aa good
good solution?
solution?
System
System Synthesis
What are
are some
some alternatives
alternatives which
which could
could
Synthesis –– What
satisfy
satisfy objectives?
objectives?
System
System Analysis
Analysis –– How
How do
do each
each of
of these
these alternatives
alternatives
perform
perform relative
relative to
to objectives?
objectives?
Optimization
Optimization –– How
How good
good can
can we
we make
make each
each alternative
alternative
perform?
perform?
DecisionDecision
DecisionMaking –– Which
Which alternatives
alternatives are
are deserving
deserving of
of
Decision--Making
further
further study?
study?
Planning
Planning for
for Action
Action –– Plan
Plan for
for the
the next
next phase
phase..
Prior to System Analysis
•• Problem
Problem Definition
you have
have established
established the
the
Definition –– you
“landscape”
“landscape” of
of the
the problem.
problem. You
You understand
understand what
what
the
the system
system needs
needs are,
are, what
what elements
elements you
you can
can alter
alter to
to
solve
solve the
the problem,
problem, and
and what
what elements
elements you
you cannot
cannot
alter.
alter.
•• Value
Value System
you have
have established
established the
the
System Design
Design –– you
objectives
objectives that
that should
should be
be met
met in
in solving
solving the
the problem.
problem.
For
For each
each objective,
objective, there
there isis some
some measure
measure that
that can
can be
be
used
used to
to determine
determine how
how well
well aa potential
potential solution
solution
satisfies
satisfies the
the objective.
objective.
•• System
System Synthesis
Synthesis –– you
you have
have identified
identified some
some
alternative
alternative solutions
solutions to
to the
the problem.
problem. These
These
alternatives
alternatives should
should pass
pass the
the feasibility
feasibility test,
test, and
and should
should
have
have some
some obvious
obvious relevance
relevance to
to satisfying
satisfying system
system
needs
needs and
and objectives.
objectives.
So What is System Analysis?
•• System
System Analysis
Analysis isis the
the development
development of
of models
models of
of the
the
alternative
alternative solutions
solutions (SA)
(SA) with
with sufficient
sufficient resolution
resolution to
to
determine
determine values
values for
for the
the measures
measures of
of effectiveness
effectiveness
(VSD)
(VSD)
•• Optimization
Optimization
–– Make
Make each
each alternative
alternative “as
“as good
good as
as possible,”
possible,” using
using the
the
models
models to
to generate
generate MOEs
MOEs to
to compute
compute “goodness”
“goodness”
•• Decision-making
Decision-making
–– Rank
Rank the
the alternatives
alternatives and
and decide
decide which
which deserve(s)
deserve(s) further
further
study,
study, using
using weights
weights obtained
obtained from
from the
the Chief
Chief Decision-Maker,
Decision-Maker,
generated
generated using
using AHP,
AHP, or
or obtained
obtained by
by interviewing
interviewing experts
experts
•• Planning
Planning for
for action
action
–– Plot
Plot aa course
course of
of action
action for
for the
the next
next iteration
iteration through
through the
the 77step
step process
process
Models
•• A
A model
model isis an
an idealization
idealization of
of part
part of
of the
the real
real
world
world that
that helps
helps in
in the
the analysis
analysis of
of aa problem
problem
–– Free-body
Free-body diagram
diagram
–– Circuit
Circuit diagram
diagram
–– Control
Control volume
volume
•• Descriptive
Descriptive vs
vs Predictive
Predictive
•• Static
Static vs
vs Dynamic
Dynamic
•• Deterministic
Deterministic vs
vs Probabilistic
Probabilistic
•• Iconic
Iconic vs
vs Analog
Analog vs
vs Symbolic
Symbolic
•• Simulation
Simulation subjects
subjects models
models to
to inputs
inputs to
to
observe
observe response
response
Descriptive vs Predictive Models
5
10
NASA Spacecraft Mass History
4
10
Mass, kg
•• Descriptive
Descriptive =
= observed
observed
or
or recorded
recorded (laboratory
(laboratory
data)
data)
•• Predictive
Predictive =
= predicts
predicts
behavior
behavior of
of “new”
“new”
system
system
•• Descriptive
Descriptive model
model
becomes
becomes predictive
predictive
when
when you
you use
use itit to
to
predict
predict behavior
behavior of
of aa
new
new system
system
•• Scatter
Scatter plot
plot of
of Spacecraft
Spacecraft
Mass
Mass vs
vs Launch
Launch Year
Year
•• AA Curve
Curve Fit
Fit could
could be
be
used
used to
to develop
develop aa
predictive
predictive model
model
3
10
2
10
1
10
0
10
1950
1960
1970
1980
1990
Launch Year
2000
2010
Static vs Dynamic Models
•• Static
Static models
models describe
describe aa system
system in
in aa steadysteadystate
state condition
condition
–– Hooke’s
Hooke’s Law
Law isis aa static
static model
model of
of structure
structure
performance
performance
–– A
A Hohmann
Hohmann transfer
transfer isis aa static
static model
model for
for orbit
orbit
transfer
transfer
•• Dynamic
Dynamic models
models describe
describe aa system
system in
in aa timetimedependent
dependent condition
condition
–– Vibration
Vibration analysis
analysis of
of aa space
space structure
structure requires
requires aa
dynamic
dynamic model
model
–– The
The trajectory
trajectory of
of aa spacecraft
spacecraft in
in an
an orbit
orbit transfer
transfer
using
using continuous
continuous thrust
thrust requires
requires aa dynamic
dynamic model
model
Deterministic vs Probabilistic Models
•• Deterministic
Deterministic models
models have
have predictable
predictable and
and
repeatable
repeatable input-output
input-output relationship
relationship
–– Integration
Integration of
of differential
differential equations
equations of
of motion
motion with
with
the
the same
same initial
initial conditions
conditions will
will give
give the
the same
same
trajectory
trajectory
•• Probabilistic
Probabilistic models
models account
account for
for system
system
uncertainties
uncertainties
–– Randomly
Randomly varying
varying the
the initial
initial conditions,
conditions, the
the
thruster
thruster performance,
performance, or
or the
the environmental
environmental effects
effects
will
will lead
lead to
to aa family
family of
of trajectories
trajectories
Iconic vs Analog vs Symbolic
•• Iconic
Iconic models:
models: flow
flow chart,
chart, blueprint,
blueprint, block
block
diagram,
diagram, free-body
free-body diagram,
diagram, bond-graph
bond-graph
diagram
diagram
•• Analog
Analog models:
models: electric
electric circuits
circuits to
to represent
represent
mechanical
mechanical systems,
systems, colors
colors on
on aa map,
map, contour
contour
lines
lines on
on aa map,
map, physical
physical model
model
•• Symbolic
Symbolic models:
models: traffic
traffic signs
signs (curve,
(curve,
intersection),
intersection), equations
equations of
of motion
motion
r
r&
&
F = mr
Earth
Moon
Mars
Models
•• A
A model
model only
only needs
needs to
to focus
focus on
on the
the aspects
aspects that
that are
are
relevant
relevant to
to the
the problem
problem
–– determine
determine those
those elements
elements of
of problem
problem definition,
definition, value
value
system,
system, and
and synthesis
synthesis that
that are
are relevant
relevant
–– determine
determine the
the relationships
relationships between
between these
these elements
elements
•• Should
Should be
be
––
––
––
––
valid
valid
manageable
manageable
able
able to
to differentiate
differentiate alternatives
alternatives
complete
complete with
with respect
respect to
to the
the value
value system
system design
design
•• Resolution
Resolution
––
––
––
binary:
binary: yes/no;
yes/no; on/off;
on/off; to
to be
be or
or not
not to
to be
be
finite
finite number
number of
of classes:
classes: color;
color; type;
type; model
model ##
real
real numbers:
numbers: thrust;
thrust; mass;
mass; height;
height; price
price
Generic System Block Diagram
En
vir
Inputs
on
m
en
t
System
Outputs
•• The
The system
system has
has inputs
inputs which
which are
are related
related to
to constraints,
constraints, isis subject
subject
to
to environmental
environmental inputs
inputs which
which are
are related
related to
to constraints,
constraints, and
and has
has
outputs
outputs which
which are
are related
related to
to needs
needs and
and objectives
objectives
Example System Block Diagram
Radiation
Payload in LEO
Commands
Drag
Solar
Gravity
Tether Launch
System
for Mars
Payloads
Magnetic field
Payload on MTO
Telemetry
More Detailed TLS System Block Diagram
Radiation
Drag
Solar
Capture
Mechanism
Tether
Power
Magnetic field
ADCS
Thermal
Payload in LEO
Commands
Gravity
Propulsion
Payload on MTO
Orbit
Telemetry
Possible Design Flow Matrix
Orbit
Tether
feedback
Orbit
Control
Propulsion
ADCS
feedforward
Power
Thermal
Example Variation on
Iterative Design Process
(from SMARTS Presentation, April 2002)
Get payload to Mars:
Tether design
Orbits
Propulsion
Survive lifetime:
Structure
Power
Reboost
Satisfy mission functions:
ADCS
Communications
C&DH
Thermal
Subsystem & Discipline Interfaces
•• Source:
Source: “An
“An Advanced
Advanced Methodology
Methodology for
for the
the Design
Design
Process
Process of
of aa Satellite,”
Satellite,” by
by Heinz
Heinz Stoewer,
Stoewer, Ralf
Ralf
Hartmann,
Hartmann, and
and L.A.J.
L.A.J. Baron
Baron von
von Richter
Richter
System Analysis and Onward
•• Develop
Develop models
models of
of appropriate
appropriate resolution
resolution for
for
each
each alternative
alternative
•• Use
Use models
models to
to calculate
calculate measures
measures of
of
effectiveness
effectiveness
•• Establish
Establish weights
weights for
for the
the Value
Value System
System Design
Design
•• Optimize
Optimize each
each alternative
alternative
•• Pick
Pick the
the best
best alternative
alternative
•• Carry
Carry the
the best
best alternative
alternative into
into the
the detailed
detailed
design
design process
process