space systems engineering: schedule module schedule module space systems engineering, version 1.0
TRANSCRIPT
Space Systems Engineering: Schedule Module
Schedule Module
Space Systems Engineering, version 1.0
Schedule Module
Space Systems Engineering, version 1.0
2Space 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.
3Space Systems Engineering: Schedule Module
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)
4Space Systems Engineering: Schedule Module
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.
5Space Systems Engineering: Schedule Module
Gantt Chart Formataka 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.
6Space Systems Engineering: Schedule Module
RRF-2 ISS-1RRF-3
First Stage
Jun
System Engineering & Integration
Gov’t Lead
ATP SRR PDR CDRDel forRRF3
Del ISS1 to KSCDel for
RRF2
Gov’t Lead SRR PDR CDR MPTADel forRRF3 Del for
US ISS-1 to KSCDel
forRRF2
Dev EngNeededCDR Del for
ISS-1
MPTA
Del for RRF-1
Jul Nov AprFab, Integ & TestUpper Stage
FY05FY05 FY06FY06 FY07FY07 FY08FY08 FY09FY09 FY10FY10 FY11FY11 FY12FY12
Flight Test/Mission Milestones
FY13FY13
ISS-2 UCM-1RRF-1
CEVATP
Contractor 1&2 SRR
Del for RRF-1
SDR PDR CDR
Del for RRF-2
Del for RRF-3
Del for ISS-1
Del for PC-1
Unpressurized payload structure
Program Integration L1 Req
Baseline Review
L2 SRR Complete
Pre-NAR Kickoff
L2 SDR
Pre-NAR Complete
PDR Complete
CDR Complete
CLVSRR
NAR
PC-1 PC-2 ISS-3
Delivery of Crew & Service Module
Delivery of Launch Abort System
Del for RRF-1
Del for RRF-3
Del for RRF-2
Del for ISS-1
Del forRRF3
Del forRRF2
Example Milestone Chart
LAS-1 LAS-2 LAS-3
LAS-4
Del for LAS-1
Del for LAS-2Del for LAS-2
Del for LAS-3
Del for LAS-4
Del for LAS-1
Del for LAS-2
Del for LAS-3
Del for LAS-4
CEV SRR
Upper Stage Engine (RS-25d/e)
Jul
CDR
Feb
PDR
ATP SRR PDR
Pre-formulation
Phase B
Phase C/D
Phase A Non-Traditional
= 0% Complete
= 100% Complete
7Space Systems Engineering: Schedule Module
Milestone or Event Charts
Example Symbols Used on Milestone Charts
Key features:
• Displays activity milestones against time.
• Lines represent duration of a single activity with appropriate start and stop milestones.
• Open triangles indicate milestones planned.
• Closed triangles indicate milestones completed.
8Space Systems Engineering: Schedule Module
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.
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.
9Space Systems Engineering: Schedule Module
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
ProgramStart
ProgramComplete
A :
4 da
ys
B : 3 days
C : 6 days
D : 5 days
F : 14 days G : 6 daysE
: 2 days
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
10Space Systems Engineering: Schedule Module
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 +
ProgramStart
ProgramComplete
A :
4 da
ys
B : 3 days
C : 6 days
D : 5 days
F : 14 days G : 6 days
E : 2 days
11Space Systems Engineering: Schedule Module
Time Estimates Used in PERT
Three estimates are required:• Most Likely, m• Optimistic, a• Pessimistic, b
Expected completion time, or mean time
te = a+4m+b6
ma b
Beta Probability Distribution
Using PERT, it is possible to determine an expected time for completion of a projectand 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.
12Space Systems Engineering: Schedule Module
Network Schedules
ADVANTAGES
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” exercises6) Provide the basis for Gantt and
milestone chart information
DISADVANTAGES
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.
13Space Systems Engineering: Schedule Module
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.
14Space Systems Engineering: Schedule Module
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 activity2. 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.
15Space Systems Engineering: Schedule Module
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)
Implementation Startto Delivery to
Assembly & Test/Instrument I&T
FlightMissions/
FlightExperiment
Projects
Assembly & Test StartTo Ship to Launch Site/
Instrument I&TStart to Delivery
To ATLO
Delivery toLaunch Siteto Launch
1 month/yearScheduleMargin
Rate2 months/year
1 week/month(2.8 months/year)
Schedule Margin
Space Systems Engineering: Schedule Module
Additional Schedule Materials
Next few slides:
Technical Performance Measures: Schedule examples for James Webb Space
Telescope (JWST)
Resource Loaded Schedules
17Space Systems Engineering: Schedule Module
James Webb Space TelescopeCumulative Milestones Tracking Chart
10
15
20
25
30
35
40
Cumulative number of milestones
* Tracking start point = 1/06
Baseline (JWST Rev E) 15 16 16 18 19 20 21 26 29 29 31 35
Actuals 15 16 16 17 18 18 18
Forecast 18 25 29 29 31 35
Mar-07 Apr-07 May-07 Jun-07 Jul-07 Aug-07 Sep-07 Oct-07 Nov-07 Dec-07 Jan-08 Feb-08
18Space Systems Engineering: Schedule Module
PROJECT TREND ANALYSIS
JWST - Total Mission Slack(June 2013 LRD)
0
2
4
6
8
10
Jan-07 Feb-07 Mar-07 Apr-07 May-07 Jun-07 Jul-07 Aug-07 Sep-07 Oct-07 Nov-07 Dec-07 Jan-08
Months of Slack
Mission Total Slack Desired Total Slack (one month per year)
19Space Systems Engineering: Schedule Module
32 876
Resource Loaded Schedules
Important to do:
– Assure no resource conflicts
- Staff being assigned efficiently
- Minimize gaps for engineering personnel (EPs)
1 4 5 9 11 12 13 14 15 16
Schedule
1) Eng EPs -- Act A -- Act B -- Act C -- Act D -- Act E -- Act F -- Act G -- Act H
2) Mfg/Test EPs -- Act A -- Act B -- Act C -- Act D -- Act E -- Act F -- Act G -- Act H
3) Test Facilities -- Act A -- Act B -- Act C -- Act D -- Act E -- Act F -- Act G -- Act H
10
33-------
11-------
---------
33-------
11-------
---------
5-3---2--
2-1---1--
---------
5-3---2--
2-1---1--
---------
3--2---1-
12--7---5-
---------
3--2---1-
12--7---5-
---------
3--2----1
10--7----3
1-------1
2---1---1
7---4---3
2---1---1
1---1----
4---4----
1---1----
1---1----
4---4----
1---1----
1----1---
4----4---
1----1---
1----1---
4----4---
1----1---
---------
---------
---------
---------
---------
---------
---------
---------
---------
---------
---------
---------
E
D
H
C
G
A
F
B
Project Complete
Months
Resources Required
Number of resources required defined for each activity, each
month
Activity C requires: 2 Eng EPs 7 Mfg/Test EPs 0 Test Facilities
20Space Systems Engineering: Schedule Module
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).
22Space 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
23Space Systems Engineering: Schedule Module
Network Schedule Example
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.
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