Schedule Module Exploration Systems Engineering, version 1.0

Transcription

1 Schedule Module Exploration Systems Engineering, version.0 Exploration Systems Engineering: Schedule Module

2 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. Exploration Systems Engineering: Schedule Module 2

3 The When: Project Schedule Provides a framework of timephased 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) Exploration Systems Engineering: Schedule Module 3

4 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. Exploration Systems Engineering: Schedule Module 4

5 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. Exploration Systems Engineering: Schedule Module 5

6 Example Milestone Chart Preformulation Phase A Phase B Phase C/D NonTraditional = 0% Complete = 00% Complete FY05 FY06 FY07 FY08 FY09 FY0 FY FY2 FY3 Flight Test/ Mission Milestones LAS LAS2 LAS3 RRF RRF2 RRF3 LAS4 ISS ISS2 UCM PC PC2 ISS3 Program Integration L Req Baseline Review PreNAR Kickoff L2 SRR Complete PreNAR Complete L2 SDR NAR PDR Complete CDR Complete CEV Delivery of Crew & Service Module ATP CEV SRR Contractor &2 SRR SDR PDR CDR LAS LAS2 LAS3 RRF RRF2 RRF3 LAS4 ISS PC Unpressurized payload structure Delivery of Launch Abort System LAS LAS2 LAS3 RRF RRF2 LAS4 RRF3 ISS CLV System Engineering & Integration Gov t Lead SRR Jun PDR Feb CDR Jul First Stage ATP SRR PDR CDR RRF RRF2 RRF3 Del ISS to KSC Upper Stage Gov t Lead SRR PDR CDR MPTA Fab, Integ & Test Jul Nov Apr Del for RRF2 RRF3 US ISS to KSC Upper Stage Engine (RS25d/e) ATP SRR PDR CDR Dev Eng Needed MPTA RRF3 Del for RRF2 ISS Exploration Systems Engineering: Schedule Module 6

7 Milestone or Event 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. Example Symbols Used on Milestone Charts Exploration Systems Engineering: Schedule Module 7

8 Gantt & Milestone Charts ADVANTAGES ) 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 ) 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. Exploration Systems Engineering: Schedule Module 8

9 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 : 5 days D Install wiring and connect to power source E Install air conditioning F Await delivery of computer G Install computer F : 4 days G : 6 days Program Start Program Complete Exploration Systems Engineering: Schedule Module 9

10 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: 4 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 : 9 days => 5 days of float + Example, Path 2: 3 days => day of float + D : 5 days F : 4 days G : 6 days Program Start Program Complete Exploration Systems Engineering: Schedule Module 0

11 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 oneofakind 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 t e = a+4m+b 6 Beta Probability Distribution Exploration Systems Engineering: Schedule Module

12 Network Schedules ADVANTAGES ) 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 DISADVANTAGES ) 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. Exploration Systems Engineering: Schedule Module 2

13 Schedule Preparation A fivestep process for schedule preparation that is commonly used in project management includes:. 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. Exploration Systems Engineering: Schedule Module 3

14 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. 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 ± week, and a clear statement of the assumptions made in the estimation process. Exploration Systems Engineering: Schedule Module 4

15 Schedule Margin Schedule Margin Rate month/year 2 months/year week/month (2.8 months/year) Flight Missions/ Flight Experiment Projects Implementation Start to Delivery to Assembly & Test/ Instrument I&T Assembly & Test Start To Ship to Launch Site/ Instrument I&T Start to Delivery To ATLO 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) Exploration Systems Engineering: Schedule Module 5

16 Additional Schedule Materials Next few slides: Technical Performance Measures: ü Schedule examples for James Webb Space Telescope (JWST) Resource Loaded Schedules Exploration Systems Engineering: Schedule Module

17 James Webb Space Telescope Cumulative Milestones Tracking Chart Cumulative number of milestones * Tracking start point = / Mar07 A pr07 May07 Jun07 Jul07 A ug07 Sep07 Oct07 Nov07 Dec07 Jan08 Feb08 Baseline (JWST Rev E) A ctuals Forecast Exploration Systems Engineering: Schedule Module 7

18 PROJECT TREND ANALYSIS 0 JWST Total Mission Slack (June 203 LRD) 8 Months of Slack Jan07 Feb07 Mar07 Apr07 May07 Jun07 Jul07 Aug07 Sep07 Oct07 Nov07 Dec07 Jan08 Mission Total Slack Desired Total Slack (one month per year) LRD = Launch Readiness Date Exploration Systems Engineering: Schedule Module 8

19 Exploration Systems Engineering: Schedule Module Resource Loaded Schedules Important to do: Assure no resource conflicts Staff being assigned efficiently Minimize gaps for engineering personnel (EPs) Schedule ) 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 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

20 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). Exploration Systems Engineering: Schedule Module 20

21 Exploration Systems Engineering: Schedule Module Backup Slides for Schedule Module

22 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 Exploration Systems Engineering: Schedule Module 22

23 Network Schedule Example Network schedule data consists of: Activities Dependencies between activities Milestones that occur as a result of one or more activities Duration of each activity H 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. Exploration Systems Engineering: Schedule Module 23