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

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.


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)


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.


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.


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


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.


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.


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


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


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.


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.


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.


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.


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


Additional Schedule Materials

Next few slides:

Technical Performance Measures: Schedule examples for James Webb Space

Telescope (JWST)

Resource Loaded Schedules


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


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)


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

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D

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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


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).


Backup Slidesfor 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


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


Example Milestone Chart

Documents

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