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Space Systems Engineering: Schedule Module Schedule Module Space Systems Engineering, version 1.0.

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Presentation on theme: "Space Systems Engineering: Schedule Module Schedule Module Space Systems Engineering, version 1.0."— Presentation transcript:

1 Space Systems Engineering: Schedule Module Schedule Module Space Systems Engineering, version 1.0

2 Space 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.

3 Space Systems Engineering: Schedule Module 3 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)

4 Space Systems Engineering: Schedule Module 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.

5 Space Systems Engineering: Schedule Module 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.

6 Space Systems Engineering: Schedule Module 6 RRF-2ISS-1RRF-3 First Stage Jun System Engineering & Integration Gov’t Lead ATPSRRPDRCDR Del for RRF3 Del ISS1 to KSC Del for RRF2 Gov’t LeadSRRPDRCDRMPTA Del for RRF3 Del for US ISS-1 to KSC Del for RRF2 Dev Eng Needed CDR Del for ISS-1 MPTA Del for RRF-1 JulNovApr Fab, Integ & Test Upper Stage FY05 FY06 FY07 FY08 FY09 FY10 FY11 FY12 Flight Test/ Mission Milestones FY13 ISS-2UCM-1 RRF-1 CEV ATP Contractor 1&2 SRR Del for RRF-1 SDRPDRCDR 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 CLV SRR NAR PC-1PC-2ISS-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 for RRF3 Del for RRF2 Example Milestone Chart LAS-1LAS-2LAS-3LAS-4 Del for LAS-1 Del for LAS-2 Del 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 ATPSRRPDR Pre-formulation Phase B Phase C/D Phase ANon-Traditional = 0% Complete = 100% Complete

7 Space Systems Engineering: Schedule Module 7 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.

8 Space Systems Engineering: Schedule Module 8 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.

9 Space Systems Engineering: Schedule Module 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 Program Start Program Complete A : 4 days B : 3 days C : 6 days D : 5 days F : 14 days G : 6 days E : 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

10 Space Systems Engineering: Schedule Module 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: 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+ Program Start Program Complete A : 4 days B : 3 days C : 6 days D : 5 days F : 14 days G : 6 days E : 2 days

11 Space Systems Engineering: Schedule Module 11 Time Estimates Used in PERT  Three estimates are required: Most Likely, m Optimistic, a Pessimistic, b  Expected completion time, or mean time t e = a+4m+b 6 m a b Beta Probability Distribution 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.

12 Space Systems Engineering: Schedule Module 12 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” exercises 6)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.

13 Space Systems Engineering: Schedule Module 13 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.

14 Space Systems Engineering: Schedule Module 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 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.

15 Space Systems Engineering: Schedule Module 15 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 Start to Delivery to Assembly & Test/ Instrument I&T Flight Missions/ Flight Experiment Projects Assembly & Test Start To Ship to Launch Site/ Instrument I&T Start to Delivery To ATLO Delivery to Launch Site to Launch 1 month/year Schedule Margin Rate 2 months/year 1 week/month (2.8 months/year) Schedule Margin

16 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

17 Space Systems Engineering: Schedule Module 17

18 Space Systems Engineering: Schedule Module 18 PROJECT TREND ANALYSIS

19 Space 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 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 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 Space Systems Engineering: Schedule Module 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).

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

22 Space Systems Engineering: 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

23 Space Systems Engineering: Schedule Module 23 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

24 Space Systems Engineering: Schedule Module 24 Example Milestone Chart


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