Download Schedule Margin - Space Systems Engineering

Schedule Module
Space Systems Engineering, version 1.0
Space Systems Engineering: Schedule Module
Module Purpose: Schedule
 To understand the different types of schedules:
Gantt chart, milestone chart, network schedules. To
recognize their advantages and disadvantages.
 To introduce the key concepts of critical path and
float as applied to network scheduling.
 To show how to prepare a schedule and estimate
activity durations.
 To introduce schedule margin recommendations.
 To discuss example schedule performance
measures and reporting formats.
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The When: Project Schedule
 Provides a framework of time-phased and coordinated activities
which represent the plan for completing the project within
established constraints.
 Used:
•
•
•
•
To integrate all elements of a project as a function of time and flow
As a communication tool across the project team
As a basis for assessing project status
For project management control
 Key inputs:
•
•
•
•
•
The work breakdown structure (WBS)
External constraints (such as imposed launch date)
Required milestones (such as technical reviews)
Major deliverables
Imposed funding profiles (can only get so much done for $X)
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Scheduling Approaches
 Gantt chart: A graphic portrayal of a project which shows the
activities to be completed and the time to complete represented
by horizontal lines drawn in proportion to the duration of the
activity.
 Milestone chart: A graphic portrayal of a project that shows the
events to be completed on a timeline.
 Network scheduling
• Critical Path Method (CPM): A graphical technique that aids
understanding of the dependency of events in a project and the
time required to complete them.
• Program Evaluation and Review Technique (PERT): A technique
based on constructing a network model of integrated activities and
events. Difference from CPM: uses statistical theory and probability
to make a determination of duration time for each task and the
likelihood of an event being on schedule.
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Gantt Chart Format
aka Bar Charts
Gantt and milestone charts are best used for
displaying the planned activities and events of
a project and the progress in meeting them.
This makes them very useful for presenting
schedule and program status information in a
concise simple format at such things as
program or activity reviews.
Because of its simplicity and ease of
interpretation, it is a particularly good tool for
communicating to higher management when
information must be presented quickly and
efficiently.
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Example Milestone Chart
FY05
FY06
FY07
FY08
FY09
Flight Test/
Mission
Milestones
Phase C/D
= 0% Complete
Phase A
Non-Traditional
= 100% Complete
Phase B
FY10
LAS-1
LAS-2
FY11
FY12
LAS-3
RRF-1 RRF-2 RRF-3 ISS-1
LAS-4
Program
Integration
CEV
Pre-formulation
Pre-NAR
Kickoff
Pre-NAR
Complete
PDR
Complete
NAR
FY13
ISS-2
PC-1
UCM-1
PC-2
ISS-3
CDR
Complete
L1 Req L2
L2
Baseline SRR
SDR
Review Complete
CEV
SRR
ATP
SDR
PDR
CDR
Contractor
1&2 SRR
Del for
LAS-1
Delivery of Crew &
Service Module
Del for
LAS-2
Del for
LAS-3
Del for
RRF-1
Del for
RRF-3
Del for
RRF-2
Del for
LAS-1
Delivery of Launch
Abort System
Del for
LAS-2
Del for
LAS-3
Del for
RRF-1
Del for Del for
ISS-1 PC-1
Unpressurized
payload structure
Del for
LAS-4
Del for
RRF-2
Del for Del for
RRF-3 ISS-1
Del for
LAS-4
CLV
System Engineering
& Integration
First Stage
Gov’t Lead
ATP
SRR
PDR
CDR
Jun
Feb
Jul
SRR
PDR
Del for
RRF-1
CDR
Del for
RRF3
Del for
RRF2
Gov’t Lead
SRR
PDR
CDR
Upper Stage
Del for
RRF3
MPTA
Fab, Integ & Test
Jul
Upper Stage
Engine (RS-25d/e)
Del ISS1
to KSC
ATP
SRR
Space Systems Engineering: Schedule Module
Nov
PDR
CDR
Apr
Dev Eng
Needed
Del
for
RRF2
MPTA
Del for
RRF3
Del for
US ISS-1
to KSC
Del for
ISS-1
Del
for
RRF2
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Milestone or Event Charts
 Key features:
• Displays activity milestones
against time.
Example Symbols Used
on Milestone Charts
• Lines represent duration of a
single activity with
appropriate start and stop
milestones.
• Open triangles indicate
milestones planned.
• Closed triangles indicate
milestones completed.
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Gantt & Milestone Charts
ADVANTAGES
1) Simple to prepare and update,
2) Information portrayed in easily
understood format,
3) Relatively inexpensive to
prepare using software tools,
4) Relate activities and calendar
dates,
5) Easy to roll up information into
summary form,
6) Useful first step for preparation
of more complex type schedules
7) Reliable estimates can be
developed when the work is
repetitive and when the product
is easy to measure
quantitatively.
Space Systems Engineering: Schedule Module
DISADVANTAGES
1) Difficult to use for detailed
schedule analysis
2) Do not show the effects of late or
early activity starts,
3) Do not represent dependencies
among activities as well as other
scheduling methods
4) Do not reflect the uncertainty in
the planned activity duration or
event date
5) Only as reliable as the estimates
on which they are based; looking
at the chart doesn’t indicate
which estimates are the most
reliable
6) Do not allow quick or easy
exploration of the consequences
of alternative actions.
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Example: Network Schedule for Computer
Installation Program
Network schedule data consists of:
•
•
•
•
Activities
Dependencies between activities
Milestones that occur as a result of one or more activities
Duration of each activity
Activity Legend:
 A - Build raised floor
 B - Build air conditioning vents
 C - Bring special power source
to computer room
 D - Install wiring and connect to
power source
 E - Install air conditioning
 F - Await delivery of computer
 G - Install computer
D : 5 days
F : 14 days
Program
Start
Space Systems Engineering: Schedule Module
G : 6 days
Program
Complete
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Example: Critical Path and Float
 Critical Path is the sequence of activities that will take the longest
to accomplish. Any delay on this path will delay the project.
•
Example: 14 days,
 Activities that are not on the critical path have a certain amount of
time that they can be delayed until they, too are on the critical path.
This time is called float (or slack).
•
•
Example, Path 1: 9 days => 5 days of float
Example, Path 2: 13 days => 1 day of float
+
+
D : 5 days
F : 14 days
Program
Start
Space Systems Engineering: Schedule Module
G : 6 days
Program
Complete
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Time Estimates Used in PERT
Using PERT, it is possible to determine an expected time for completion of a project
and the likelihood (probability) that this expected completion time will be met.
Projects best suited for PERT are one-of-a-kind complex programs that involve new
technology or processes and research and development.
 Three estimates
are required:
• Most Likely, m
• Optimistic, a
• Pessimistic, b
 Expected
completion time,
or mean time
a
m
b
te = a+4m+b
6
Beta Probability Distribution
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Network Schedules
ADVANTAGES
DISADVANTAGES
1) Provide graphical portrayal of
project activities and
relationships/constraints
2) Force communications among
team members in identifying
activities
3) Organize what would otherwise
be confusing material, making it
easier for managers to make
tradeoffs and develop
alternative plans
4) Give managers more control
over activities/events and
schedules
5) Facilitate “what if” exercises
6) Provide the basis for Gantt and
milestone chart information
1) Network construction can be
difficult and time consuming.
2) Only as sound as the activity time
and resource estimates.
3) Sometimes difficult to portray
graphically—too many lines,
nodes and intersections.
4) Not particularly good for
conveying information in
briefings/reviews.
5) Complex networks, once
sketched out on a large wall
chart, tend to become the focus
of management attention when,
in fact, a manager should be
paying attention to factors not on
the chart, such as management/
labor relations.
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Schedule Preparation
A five-step process for schedule preparation that is commonly used in
project management includes:
1. •Activity definition - what has to be accomplished?
2. •Activity sequencing - what has to occur first, second…?
3. •Activity duration estimation - how long does activity take?
4. •Schedule development - what are realistic start & finish dates?
5. •Schedule control - how to manage changes & track performance?
 Risk is inherent in all programs, and scheduling is one element of risk.
Uncertainty introduced in estimating the duration of each activity
causes most schedule risk. Project managers must assess the
likelihood of failing to meet schedule plans and the impact of that
failure. Probabilistic techniques have proven to be very useful in
conducting these assessments.
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Activity Duration Estimating
 Activity duration estimating is the determination of the time required to
complete the activities that make up the project.
 This is one of the most difficult aspects of schedule development and
should be performed by people who are most familiar with the activity.
 Two key inputs to the estimation process
1. the resources/workforce required and assigned for the activity
2. the capabilities of the resources assigned.
The following techniques are commonly used in estimating activity
durations:
 Expert judgment guided by historical information,
 Analogous estimating based on experience of similar programs,
 Parametric estimating based on formulas describing relationships
among project parameters and time, and
 Use of simulation to develop distributions of probable duration of each
activity.
Note: If probability distributions not used, then estimates should include a
range of possible values, e.g., 3 weeks ± 1 week, and a clear statement
of the assumptions made in the estimation process.
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Schedule Margin
Schedule
Margin
Rate
Flight
Missions/
Flight
Experiment
Projects
1 month/year
2 months/year
Assembly & Test Start
Implementation Start
To Ship to Launch Site/
to Delivery to
Instrument I&T
Assembly & Test/
Start to Delivery
Instrument I&T
To ATLO
1 week/month
(2.8 months/year)
Delivery to
Launch Site
to Launch
Definitions:
Total Schedule = Critical Path (i.e., Planned Activities) + Schedule Margin
Schedule Margin = No Planned Activities, but Funded Schedule
Schedule Margin Rate = Schedule Margin/(Planned Activity + Schedule Margin)
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Additional Schedule Materials
Next few slides:
Technical Performance Measures:
 Schedule examples for James Webb Space Telescope
(JWST)
Resource Loaded Schedules
Space Systems Engineering: Schedule Module
James Webb Space Telescope
Cumulative Milestones Tracking Chart
35
* Tracking start point = 1/06
Cumulative number of milestones
40
30
25
20
15
10
Mar-07
Apr-07
May-07
Jun-07
Jul-07
Aug-07
Sep-07
Oct-07
Nov-07
Dec-07
Jan-08
Feb-08
Baseline (JWST Rev E)
15
16
16
18
19
20
21
26
29
29
31
35
Actuals
15
16
16
17
18
18
18
25
29
29
31
35
Forecast
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PROJECT TREND ANALYSIS
JWST - Total Mission Slack
(June 2013 LRD)
10
Months of Slack
8
6
4
2
0
Jan-07
Feb-07
Mar-07
Apr-07
May-07
Mission Total Slack
Space Systems Engineering: Schedule Module
Jun-07
Jul-07
Aug-07
Sep-07
Oct-07
Nov-07
Dec-07
Jan-08
Desired Total Slack (one month per year)
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Resource Loaded Schedules
Important to do:
Months
– Assure no
resource
conflicts
1
Schedule
2
3
5
6
7
8
9
10
11
12
13
14
15
16
A
B
- Staff being
assigned
efficiently
- Minimize gaps
for engineering
personnel
(EPs)
4
C
F
D
G
E
Project Complete
H
Resources Required
1) Eng EPs
-- Act A
-- Act B
-- Act C
-- Act D
-- Act E
-- Act F
-- Act G
-- Act H
3
3
-
3
3
-
5
3
2
-
5
3
2
-
3
2
1
-
3
2
1
-
3
2
1
2
1
1
1
1
-
1
1
-
1
1
-
1
1
-
-
-
-
-
2) Mfg/Test EPs
-- Act A
-- Act B
-- Act C
-- Act D
-- Act E
-- Act F
-- Act G
-- Act H
1
1
-
1
1
-
2
1
1
-
2
1
1
-
12
7
5
-
12
7
5
-
10
7
3
7
4
3
4
4
-
4
4
-
4
4
-
4
4
-
-
-
-
-
3) Test Facilities
-- Act A
-- Act B
-- Act C
-- Act D
-- Act E
-- Act F
-- Act G
-- Act H
-
-
-
-
-
-
1
1
2
1
1
1
1
-
1
1
-
1
1
-
1
1
-
-
-
-
-
Space Systems Engineering: Schedule Module
Number of resources
required defined for
each activity, each
month
Activity C requires:
2 Eng EPs
7 Mfg/Test EPs
0 Test Facilities
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Module Summary: Schedule
 There are different methods for displaying project schedule information.
 Gantt and Milestone charts relate activities to calendar dates in an
easily understood format.
 Network schedules show the dependencies between activities in a
graphical portrayal with activity durations.
 Critical Path is the sequence of activities that will take the longest to
accomplish. Any delay on this path will delay the project. Activities that
are not on the critical path have a certain amount of time that they can
be delayed until they, too are on the critical path. This time is called
float (or slack).
 There is inherent risk in developing schedules. Probabilistic techniques
can be used to assess the risk.
 For space missions, guidelines exist for determining schedule margin.
 Schedule information, such as the accomplishment of milestones or the
amount of schedule slack, can be used to report project status/progress
(as a form of technical performance measures).
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Backup Slides
for Schedule Module
Space Systems Engineering: Schedule Module
Additional Schedule Topics
Additional topics if you are interested in adding to the lecture:
 Earned Value Management (EVM)
• A tool for measuring and assessing project performance through
the integration of technical scope with schedule and cost objectives
during the execution of the project. EVM provides quantification of
technical progress, enabling management to gain insight into
project status and project completion costs and schedules. Two
essential characteristics of successful EVM are EVM system data
integrity and carefully targeted monthly EVM data analyses (i.e.,
risky WBS elements).
• One can dedicate an entire lecture just on EVM. Note that many
contractors and government agencies have entire courses devoted
to teaching EVM.
 Schedule Software Tools, such as
• Microsoft Project
• Primavera
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Network Schedule Example
H
Network schedule data consists of:
• Activities
• Dependencies between activities
• Milestones that occur as a result
of one or more activities
• Duration of each activity
Space Systems Engineering: Schedule Module
In this example, the lines represent
project activities A through H; the
nodes represent the events
associated with the beginning and
end of the activities. The network
shows the following constraints
among the activities: activity A
must be completed before activities
B, C, or D can begin; B must be
completed before E can begin; F
cannot begin until D is completed;
G cannot begin until C and E are
done, and H cannot begin until F
and G are completed. In addition
to showing this type of sequencing
constraints, network schedules can
also show the time and resources
planned for each activity and thus
provide managers with a
mechanism to monitor and control
the project.
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Example Milestone Chart
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