Team 5: Mission Support Report

Aerospace and Ocean Engineering

Virginia Tech

Blacksburg, VA

Team Members:

Aurelien Borgoltz Patrick Hagan Scott Lennox

Chris Zuchowski

16 November 2001

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TABLE OF CONTENTS

List of Tables.......................................................................................................................iii List of Figures ..................................................................................................................... iv Abbreviations ....................................................................................................................... v List of Symbols ..................................................................................................................vii Chapter 1 – Introduction ...................................................................................................... 1

1.1 Elements of Mission Support .................................................................................... 2 1.1.1 Program Management ........................................................................................ 2 1.1.2 Cost Modeling and Reliability ........................................................................... 3 1.1.3 Mission Operations And Ground Systems ......................................................... 4 1.1.4 Economic, Political, and Legal Issues................................................................ 4

1.2 Summary and Overview............................................................................................ 5 Chapter 2 – Subsystem Modeling ........................................................................................ 7

2.1 Program Management ............................................................................................... 7 2.2 Cost and Reliability Modeling .................................................................................. 8

2.2.1 Cost Modeling.................................................................................................... 8 2.2.2 Reliability Modeling ........................................................................................ 16

2.3 Mission Operations and Ground Systems ............................................................... 19 2.3.1 Mission Operations .......................................................................................... 19 2.3.2 Ground Systems ............................................................................................... 20

2.4 Political, Legal, and Environmental Issues ............................................................. 22 2.4.1 Political And Legal Issues................................................................................ 22 2.4.2 Environmental Issues ....................................................................................... 23

2.5 Subsystem Interaction Modeling............................................................................. 24 2.6 Summary and Overview.......................................................................................... 26

Chapter 3 – Mission Support Examples............................................................................. 28 3.1 Cost Modeling......................................................................................................... 28 3.2 Reliability................................................................................................................ 32 3.3 Ground Stations....................................................................................................... 34

Chapter 4 – Summary and Conclusions ............................................................................. 37 4.1 – Program Management .......................................................................................... 37 4.2 – Cost Modeling and Reliability ............................................................................. 38 4.3 – Mission Operations and Ground Support............................................................. 40 4.4 – Summary .............................................................................................................. 40

References .......................................................................................................................... 42

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LIST OF TABLES

Table 2.1 – Parametric Cost Estimation Process ............................................................... 10 Table 2.2 – Space Mission Characteristics for Parametric Cost Modeling........................ 12 Table 2.3 – Cost-Estimation Relationships for Earth-Orbiting Satellites Including RDT&E

and TFU .......................................................................................................... 14 Table 2.4 – Software Development Costs.......................................................................... 15 Table 2.5 – Ground Segment Development Cost Model ................................................... 15 Table 2.6 – Operations and Support Costs in FY00$......................................................... 16 Table 2.7 – Antenna and Communications Electronics Costs ........................................... 16 Table 2.8 – Element Interaction Matrix ............................................................................. 25 Table 3.1 – FireSat Costs for RDT&E and TFU................................................................ 31 Table 3.2 - FireSat Ground Segment and Operations Costs in FY00$M........................... 32 Table 3.3 - FireSat Annual Operations and Maintenance Cost in FY00$M...................... 32 Table 3.4 - FireSat Life-Cycle Cost Estimate in FY00$M ................................................ 32

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LIST OF FIGURES

Figure 1.1 – Lightweight matrix organization .................................................................... 1

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ABBREVIATIONS

ADCS Attitude Determination and Control System BOL Beginning of Life CBS Cost Breakdown Structure C&DH Command and Data Handling CER Cost Estimation Relationship DH Data Handling DomSat Domestic Satellite DOT Department of Transportation DSN Deep Space Network EOL End of Life EPS Electrical Power System EVA Extreme Value Analysis FY00$K Thousands of Fiscal Year 2000 Dollars GSE Ground Support Equipment Guid & Nav Guidance and Navigation HETE High Energy Transient Experiment HST Hubble Space Telescope IA&T Integration, Assembly & Test JPL Jet Propulsion Laboratory JSC Johnson Space Center KLOC Thousands of Lines of Code LEO Low Earth Orbit LOOS Launch & Orbit Operations Support LV Launch Vehicle MCC Mission Control Center NASA National Aeronautics and Space Administrations NRL Naval Research Labs RAM Random-Access Memory RDT&E Research, Development, Testing and Evaluation RF Radio Frequency ROM Read-Only Memory RSS Root sum squared RTG Radioisotope Thermal Generator SE Standard Error SHF Super High Frequency SMAD Spacecraft Mission Analysis and Design SSCM Small Satellite Cost Model TDRS Tracking Data and Relay Satellite System TFU Theoretical First Unit TT&C Telemetry Tracking & Command UHV UltraHigh Frequency US United States

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VHF Very High Frequency WBS Work Breakdown Structure

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LIST OF SYMBOLS

b Data rate (bits/sec) D Antenna diameter (meters) d Antenna range (km) EQ Equipment cost F Probability component will fail FAC Facilities cost fC Frequency carrier (Hertz) R Probability component will operate without failure Ra Reliability of component Rp Parallel reliability SW Software costs t Time tp Transmitter power (watts) λ Component failure rate σ Standard Deviation

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CHAPTER 1 – INTRODUCTION

The organization of this project can be described as a functional, or lightweight

matrix organization. That is, the personnel working on the project are divided until

function subgroups, each of which will address a particular set of functional issues. An

example of a lightweight matrix organization is shown in Figure 1.1. Although members

of each functional group may work more on a single project, the design process is

dominated by the division of members of each project into the functional subgroups,

allowing for greater access to information which may be useful to multiple projects.

Figure 1.1 – Lightweight matrix organization

The mission support team is responsible for much of the engineering design

which is not often considered engineering, but is in fact critical to the engineering design

process. The design process is broken into five smaller parts:

- Team 1 is responsible for the astrodynamics, mission analysis, mission

geometry, and guidance and navigation, propulsion, and the attitude

determination and control system (ADCS)

- Team 2 is responsible for communications as well as command and data

handling (C&DH)

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- Team 3 is responsible for the power and thermal systems, including analysis

of the environment in which the craft will operate

- Team 4 is responsible for the structures and mechanisms of the vehicle and is

given the task of launch vehicle selection

- Team 5 is responsible for mission support

This report describes in detail the activities of the mission support team with regard to the

overall design process, and how it interacts with the other subsystems.

1.1 Elements of Mission Support

There are four elements the mission support subsystem. The four elements are

program management, cost modeling and reliability, mission operations and ground

systems, and economic, political and legal issues. This report addresses all the parts of

each element which will combine to form the complete subsystem.

1.1.1 Program Management

Program management deals with the development of a schedule for the project,

how the work will be distributed throughout the team, keeping track of action items, and

the management of the group meetings. There are several specialized tools which

program managers may take advantage of in order to run a more efficient project. One

example is the Work Breakdown Structure (WBS) which is a table used to categorize and

normalize project tasks and costs. A WBS covers all phases of the project, from concept

development to the end of operations.

Another tool used is the Gant chart. A Gant chart identifies each action time with

a unique ID number and uses color and size coded lines across the calendar to visually

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show the nature of the task, the progress of the task, due dates, and how tasks relate to

each other by connecting lines which pair the end of one task to the beginning of the next

task in a sequence.

1.1.2 Cost Modeling and Reliability

Cost modeling and reliability deals with the project budget, how money will be

allocated to the different areas of the project, and parametric cost evaluation. Reliability

estimation, system modeling, and analysis must also be completed. A large portion of

any design’s budget will consist of launch vehicle costs.

The launch vehicle cost depends on the vehicle selected by the structures and

mechanisms team. They are responsible for selecting the launch vehicle that best suits

the mission needs and objectives. Once this step has been completed, the mission support

team must incorporate the cost of this vehicle into the overall cost model.

The cost model should describe the elements that contribute to the total cost of the

mission, a cost comparison of alternative systems, and the sensitivity of mission cost to

alternatives. Several parameters must be taken into account to obtain an accurate cost

model. The principal parameters for this project are the mass, power system, and

performance. Variation in any of these parameters will affect the total cost of the system.

It is the objective of the cost model to determine which alternative systems give the

highest performance value while keeping cost within budget constraints.

Reliability is also a key factor of space projects. If a system fails while the

spacecraft is in orbit, it cannot be easily repaired, so a great deal of attention is paid to the

reliability of each part of a given subsystem. By definition, reliability is “the probability

that a device will function without failure over a specified time period or amount of

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usage.”14 Reliability analysis can be described in terms of a failure analysis. In such

analysis, attention must be focused on how any part of the subsystem could fail, and how

to prevent the loss of the whole mission because of that failure.

1.1.3 Mission Operations And Ground Systems

Mission operations and ground systems are a major portion of the mission

support team. Determining the spacecraft goals, the operations team functions, the

operations timeline, the interface with other operations centers, the ground system’s

functions are and the number of ground stations needed are all included in the mission

operations and ground systems element.

1.1.4 Economic, Political, and Legal Issues

The economic, political and legal element deals with the relevant issues of the

world and space industry. Part of responsibilities of the team is to determine what a

spacecraft can do without breaking international laws or treaties. Determining the

agencies that would be involved with the spacecraft must also be accomplished.

One must consider the Outer Space Treaty9 when examining the political and

legal issues involved in space vehicle design. Article IV of the Treaty states that

signatories of the Treaty are “not to place in orbit around the Earth any nuclear weapons

or any other kinds of weapons of mass destruction, install such weapons on celestial

bodies, or station such weapons in outer space in any other manner.”9 One must consider

the possibility of using a space platform used to launch vehicles through a momentum

exchange system platform to de-orbit vehicles or projectiles with the intent of attacking

other nations. Therefore safeguards must be in place to ensure the proper use of such a

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launch platform, perhaps through international oversight or automatic safeguards in the

launch system. Even with such precautions there may be the risk of accidental loss of

vehicles, which have the potential to survive reentry and causing collateral damage upon

impact.

In the case of accidental loss of a vehicle that re-enters and causes damage to

another signatory of the Treaty, the parties responsible for launching the vehicle are

responsible for damages incurred, as under Article VII. The State Signatory of the Treaty

from which the vehicle is launched is responsible for overseeing all activities of non-

government agencies involved in space flight as per Article VI. A non-government

venture may need to increased overhead to comply with government specifications for

the program. Both government and private ventures will be responsible for receiving

insurance that provides coverage both in the case of the loss of the payload and for the

possibility of collateral damage caused by a launch gone awry.

In all of the elements, documentation of analysis and decisions must be done.

Everything that is done in the design team should be documented so that someone not

already familiar with the project could understand why certain choices were made. The

documentation will also help in the preparation for design reviews. Decisions must be

documented as they are made in order to retrace the design process at a later time when

past decisions are not easily remembered.

1.2 Summary and Overview

The remainder of this report is dedicated to describing, in greater detail, aspects of

each subsection. Chapter 2 describes the system of modeling used when performing cost

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and reliability analysis, creating conceptual mission operations and ground support

infrastructure, the political and economic portions of a design, and how each subsystem

interacts with others in the same project. Chapter 3 gives several examples of how

previous designs have performed cost analysis and formed their mission operations and

ground crew, as well as what type of components are needed to form the mission support

subsystem and more technical information regarding the assembly of a mission

operations and ground crew. It describes in greater detail the specifics of the political and

legal issues involved in designing spacecraft. Chapter 4 concludes the report by

summarizing important points and drawing conclusions on the nature of the mission

support team.

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CHAPTER 2 – SUBSYSTEM MODELING

In this chapter, the program management team’s responsibilities are described and

the equations used to model the goals of the team are introduced. Cost and reliability

modeling are introduced, as well as the concepts behind modeling program management,

scheduling, ground stations, and mission support. Analysis is also performed to describe

how all subsystems will interact when brought together in the same project.

2.1 Program Management

Modeling program management is an abstract task at best. The first task of the

program management team is to develop a division of responsibility for all other

subsystems. Program management is also responsible for building up synergetic relations

between the program management and the subsystems and between the subsystems

themselves.

Another objective for the program management team is to set up and maintain a

meeting schedule. These meetings should be done on a regular basis. The program

management team requests each subsystem to describe its progress, problems and plan of

action between meetings. The program management team records the information

generated at each meeting and reports it to the project supervisor or the responsible

agency involved in the program. Project meetings are run by the program management

team and follow a defined schedule. An agenda is formed where all the information cited

previously is recorded. Such a way of sharing information produces two benefits: it

makes it possible for each subsystem to know its place within the design project as well

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as in the schedule, and in the case of a change of managing team, the incoming managers

are able to carry on from where the project was suspended.

The program management is also responsible for reviewing, approving and

monitoring the progress and development of each subsystem. At the same time, the

program management team must understand the program interdependencies, maintain the

program management structure to ensure an effective team, and ensure that the program

requirements are met.

The financial responsibilities of the program management team make up a large

part of its duties. The program management team must allocate funds to each of the

subsystems according to a Cost Breakdown Structure (CBS) and ensure the appropriate

acquisition and distribution of resources. Such control over the budget shall support the

budget program of the involved agency.

The program management team must also report its activities to their own

superiors. The program management team must ensure that for each step of the design

process the overseeing agency or company is satisfied on both performance and cost

according to the requirements and constraints initially set forth. Ensuring that the

infrastructure needed to complete the project is available and that program schedule is

respected will also be part of the program management team responsibilities.

2.2 Cost and Reliability Modeling

2.2.1 Cost Modeling

The cost of a project depends on many, often ill-defined, parameters. The process

of cost modeling is an effort to predict the overall cost of the project, from initial research

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and testing to its final end-of-life costs. Cost modeling is often used as a method of

maximizing performance while remaining within budgetary constraints rather than

estimating the cost of a project with given performance parameters14.

The first step in developing a preliminary cost model is to determine cost analysis

and descriptions from mission parameters. These parameters are then used as factors

known as cost drivers that serve as inputs into the selected cost model14.

There are several types of cost models that may be used, but an ever increasingly

popular method of cost modeling is the parametric estimation method, which uses

mathematical relationship to relate the input parameters directly to the cost of the project.

The equation used is known generally as the Cost Estimation Relationship (CER) and is

expressed as a function of the cost drivers. The CER may also include complexity factors

to account for changes in technology and for the learning curve associated with the

assembly of multiple spacecraft14.

When using a cost modeling method there are several assumptions that must be

made regarding the future national financial status. Some of these are general

assumptions and some are specific to the parametric cost estimation method. These

assumptions include, but are not limited to14:

- Costs listed in constant-year dollars

- Inflation rate forecasts

- Exclusion of contractor fees and costs of government project offices

- Inclusion of costs of government furnished equipment

- Inclusion of learning curve

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Specific to the parametric cost estimation method are two assumptions. First, because

this method uses historical costs to characterize cost trends, major shifts in technology or

methodology may create discrepancies between the cost estimation and the actual cost14.

Second, because cost has many variables that cannot be determined and thereby taken

into account in any cost estimation model, there is a certain amount of error (known as

the standard error, SE) associated with any cost model14. This error can often be

estimated as well to give a range of costs. Lowering this error is a primary goal of any

cost estimation model.

Table 2.1 – Parametric Cost Estimation Process Adapted from Ref. 14

Step Description 1. Develop Work Breakdown Structure Identify all cost elements

Organized to categorize and normalize costs

Covers all phases of the project

2. List Space System Characteristics

see Table 2.2, Ref. 14

3. Compute Space Segment Costs RDT&E Costs Software Costs TFU costs Subsequent unit costs

4. Computer Launch Segment Costs LV costs + cost per kilogram of payload

5. Compute Ground Segment Costs First ground station Software costs Additional ground station costs

6. Computer Operational and Maintenance Costs

Space segment spares Launch cost for spares Ground systems operations and support

7. Life-Cycle Costs Sum of 3 – 6

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The parametric cost estimation process can be divided into seven steps to simplify

the process. These steps are summarized in Table 2.114. The first of these steps is the

creation of a Work Breakdown Structure and the gathering of historical information and

examples. The WBS serves as an organizational table to categorize and normalize the

costs of the project and covers all phases of the project. Second, a list of spacecraft

characteristics must be generated. An example of characteristics can be found in Table

2.214. These characteristics will be used as cost drivers in the cost model. Third, the cost

of the space segment of the project must be generated. This includes Research,

Development, Testing, and Evaluation (RDT&E) costs, software costs, theoretical first

unit (TFU) costs, and subsequent unit costs. Fourth, the launch segment costs are to be

calculated including launch vehicle, facilities, and insurance costs. Fifth, the ground

segment costs must be found including the first ground station costs, software costs, and

additional ground station costs. Next operations and maintenance costs including space

segment spares, launch costs for spares, and the ground systems operations and support

costs must be determined. Finally, the life-cycle costs may be estimated by summing the

cost of steps 3 – 6. This sum represents the total cost of the project.

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Table 2.2 – Space Mission Characteristics for Parametric Cost Modeling Adapted from Ref. 14

Characteristic Examples Constellation Number of spacecraft

Orbital altitude

External Communications Resources

TDRS DomSat

Space Segment Payload

Type Weight

Bus Weight by subsystem Volume ADCS accuracy and knowledge Stabilization type Flight software lines of code Average power Solar array area Battery capacity Data storage capacity Number of thrusters

Launch Segment Launch vehicle Upper stage Launch site Number of spacecraft per launch

Ground Segment Number of sites Software language and lines of code New and existing equipment and facilities Communications operating frequency

Mission Operations and Support Mission Duration

Number of personnel Number of spare units Number of support flights

2.2.2.1 Space Segment Costs

The cost of much of the space segment of the design is based upon the specific

costs of sensors and payload for the spacecraft and is therefore difficult to predict in a

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general sense for all sensors available. For some payloads that are typical to space

missions there is enough historical data to determine a cost model. However, costs for

the spacecraft bus may be generally predicted using empirical costs. Table 2.314 lists

components, exemplary parameters, and the estimated cost and the SE associated with

each component for the space segment of the mission, including RDT&E and TFU costs,

as adapted from Ref. 14. These equations are valid to approximately within ±25% within

the data range given.

A cost not discussed in Table 2.3 is the cost associated with software for ground

and flight computers. Table 2.414 lists costs associated with both custom flight and

ground software using several different languages. After calculating the approximate

lines of code necessary for the software, the base cost can be calculated as below and

multiplied by the appropriate language factor. These factors are based on the level of

usage each language has seen in the field and likely experience programmers will have

with it. The information in this table does not list some languages such as C++ or

MatLab and thus we should expect an even higher factor for these languages if they are

used.

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Table 2.3 – Cost-Estimation Relationships for Earth-Orbiting Satellites Including RDT&E and TFU – Adapted from Ref. 14 Cost Component Parameter X (unit) Input Data

Range Subsystem Cost CER*

(FY00$K) SE (FY00$K)

1. Payload Spacecraft Total Cost (FY00$K)

1,922 – 50,651 0.4 X 0.4 × SEbus

2. Spacecraft Satellite bus dry mass (kg)

20 – 400 781 + 26.1 X 1.261 3,696

2.1 Structure† Structures mass (kg) 5 – 100 299 + 14.2 X ln(X) 1,097 2.2 Thermal‡ Thermal control mass

(kg) 5 – 12 246 + 4.2 X 2 119

Average Power (W) 5 – 410 -183 + 181 X 0.22 127 Power system mass (kg)

7 – 70 -926 + 396 X 0.72 910

Solar array area (m2) 0.3 – 11 -210,631 + 213,527 X 0.0066

1,647

Battery capacity (A-hr)

5 – 32 375 + 494 X 0.754 1,554

BOL Power (W) 20 – 480 -5,850 + 4,629 X 0.15 1,585

2.3 Electrical Power System (EPS)

EOL Power (W) 5 – 440 131 + 401 X 0.452 1,603 TT&C/DH mass (kg) 3 – 30 357 + 40.6 X 1.35 629 2.4a Telemetry

Tracking & Command (TT&C)**

Downlink data rate (Kbps)

1 – 1,000 3,636 – 3,057X-0.23 1,246

TT&C + DH mass (kg)

3 – 30 484 + 55 X 1.35 854 2.4b Command & Data Handling Data Storage

Capacity (MB) 0.02 – 100 -27,235 + 29,388 X0.0079 1,606

ADCS dry mass (kg) 1 – 25 1,358 + 8.58 X 2 1,113 Pointing Accuracy (deg)

0.25 – 12 341 + 2651 X –0.5 1,505 2.5 ADCS

Pointing Knowledge (deg)

0.1 – 3 2,643 – 1,364 ln(X) 1,795

Satellite Bus dry mass (kg)

20 – 400 65.6 + 2.19 X 1.261 310

Satellite volume (m3) 0.03 – 1.3 1539 + 434 ln(X) 398

2.6 Propulsion††

Number of Thrusters 1 – 8 4,303 – 3,903 X –0.5 834 3. Integration, Assembly, & Test (IA&T)

Spacecraft total cost (FY00$K)

1,922 – 50,651‡‡

0.139 X 0.139 × SEbus

4. Program Level Spacecraft total cost (FY00$K)

1,922 – 50,651‡‡

0.229 X 0.229 × SEbus

5. Ground Support Equipment

Spacecraft total cost (FY00$K)

1,922 – 50,651‡‡

0.066 X 0.066 × SEbus

6. Launch & Orbital Operations Support (LOOS)

Spacecraft total cost (FY00$K)

1,922 – 50,651‡‡

0.061 X 0.061 × SEbus

* CER based on the Small Satellite Cost Model [Bearden, Boudreault, and Wertz, 1996]. † Aluminum materials primarily selected use of advanced materials (e.g. composites, magnesium). ‡ Thermal CER appropriate for passive systems only. ** CER applies to UHF/VHF and S-band LEO systems. †† Hydrazine monopropellant and cold-gas stationkeeping systems only. CER not appropriate for

bipropellant or dual-mode systems. Costs of apogee kick motor are not included. ‡‡ Input data range for items 3 – 6 calculated using min and max values of input range for item 2.

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Table 2.4 – Software Development Costs Adapted from Ref. 14 Flight Software 435 × KLOC Ground Software 220 × KLOC KLOC = Thousand of Lines of Code; cost without fee FACTORS FOR OTHER LANGUAGES Language Factor Ada 1.00 UNIX-C 1.67 Pascal 1.25 FORTRAN 0.91

We must also more closely examine the costs associated with the ground segment

and operational costs of the mission. Such costs are difficult to determine during the

conceptual phase of the project since they often include inputs such as building square

footage required and specific equipment requirements. By examining past space

missions we may develop a model which relates a cost which is predictable, such as

software costs, to the cost of other components of a mission. Table 2.514 shows how the

cost of software can be used to approximate the cost of many other factors as well as the

total ground segment cost.

Table 2.5 – Ground Segment Development Cost Model Adapted from Ref. 14

Ground Station Element Development Cost Distribution (%) Development Cost as

Percent of Software Cost (%) Facilities (FAC) 6 18 Equipment (EQ) 27 87 Software (SW) 33 100 Logistics 5 15 Systems Level Management 6 18 Systems Engineering 10 30 Product Assurance 5 15 Integration and Test 8 24

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We can derive the cost of each of the other elements by using the relationship between

software costs and other development costs established in the right hand column of table

2.5. Using the central column we can determine what percentage of the total cost each

element accounts for. The operations and support costs can then be found using the total

cost of the ground segment, as shown in Table 2.614.

Table 2.6 – Operations and Support Costs in FY00$ Adapted from Ref. 14 Maintenance 0.1 × (SW + EQ +FAC)/year Contractor Labor $160K/Staff Year Government Labor $110K/Staff Year

A final cost associated with the ground segment is the communications equipment

necessary to control the satellite. A large base of cost knowledge is available to predict

the cost of similar equipment in the future because this same type of equipment is often

used on similar space missions. Using Table 2.714 and equation 2.714, we can calculate

the cost associated with the most likely forms of antenna equipment to be used. Note that

this cost does not include personnel or facilities to house the antenna.

Table 2.7 – Antenna and Communications Electronics Costs Adapted from Ref. 14

Frequency Cost (FY00$K) SHF (50 × D) + (400 × P) + 1800 K, C Band 640 Ku Band 750 D = antenna diameter in m P = RF power in kW

2.2.2 Reliability Modeling

Reliability is a significant parameter that must be considered throughout a

spacecraft’s design. A spacecraft system’s reliability is a quantifiable element that can be

controlled by spacecraft designers. After first identifying possible failure modes, designs

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may be altered to either eliminate failures or limit them to satisfactory levels. Design

margins, simplification, and redundancies are tools used to improve the overall reliability

of a system.

2.2.2.1 Failures

Failures can be subdivided into two basic categories: random and wear-out

failures. Random failures are those which cannot be accurately predicted. However, by

accounting for their existence, engineers can take the necessary steps to ensure a tolerant

design. Wear-out failures are those which either occur as a result of a components

general use or due to the effects of an unfavorable environment. A battery is a typical

example of a component prone to wear-out failure. Some failure modes can be further

classified as being single-point failure modes. A single-point failure is one which causes

mission failure14. A malfunction in the deployment of a solar array could be a single-

point failure for some spacecraft.

There are many tools that engineers can use to improve the reliability of their

spacecraft. Design margins can make up for manufacturing errors, deficiencies in

analysis, and other unexpected circumstances. Design margins are frequently used in a

spacecraft’s thermal design by allowing for a component’s survival beyond maximum

expected temperatures. Past space missions have also shown that the complexity of a

system’s design has a direct effect on reliability. For instance, an active 3-axis stabilized

satellite has a far greater chance of failure than a satellite which is gravity-gradient

stabilized. The advantages gained by complex systems must be weighed against the

systems reduced reliability. One must recall overall mission goals when comparing the

benefits of a complex system with the reliability found in simpler systems.

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The use of redundant systems is a common practice used to improve system

reliability. In general, redundancy is the inclusion of multiple components which can

fulfill the same needs. Sometimes this consists of two or more identical components

which use switching to control which component is actively used. An alternative to using

identical components is diverse design redundancy, which uses two or more components

of different designs. Diverse design redundancy offers reliable protection against design

deficiencies, but incurs costs in added design time, manufacturing, testing, and mass.

2.2.2.2 Equations

The basic equation for expressing the reliability of a component not subject to

wear-out failures is14:

teR λ−= (2.1)

where λ is the failure rate and t is the time, and R is the probability that the component

will operate without failure for time t. The probability of failure, F, can be found using14:

RF −=1 (2.2)

For a system comprised of n nonredundant elements, all equally essential for operation,

the system reliability, Rs, is found using14:

∑== −∏ tn

iSieRR λ

1

(2.3)

where Ri (i = 1…n) is the reliability and λ i is the failure rate of the individual elements.

For reliabilities greater than 0.9, the following simplification may be used14:

te t λλ −≈− 1 (2.4)

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When systems involve n parallel components, all of which can individually satisfy the

systems requirements (redundant components), the components are said to be in parallel

and the following expression is used14:

( )∏ −−=n

ip RR1

11 (2.5)

where Rp is the parallel reliability. When the individual reliability of each element in

equation 2.5, the expression simplifies to14:

nap RR )1(1 −−= (2.6)

where Ra is the reliability of the components, and n is the number of components.

These equations give numerical representations of a system’s reliability. After

setting specific spacecraft reliability goals, the equations allow the design to be iterated

and progress measured in an orderly manner.

2.3 Mission Operations and Ground Systems

2.3.1 Mission Operations

According to Larson and Wertz14, mission operations is the collection of activities

preformed by operations teams during the flight phase of the mission, together with the

operations design activities they perform pre-launch, including development of a mission

operations concept, policies, data flows, training plans, staffing plans, and cost estimates.

The mission operations are split up into four important elements10. These four elements

are mission analysis and planning, the mission control center (MCC), remote tracking,

telemetry, and command stations and the communications network between the MCC and

the remote stations10.

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As described in Ref. 4, mission analysis and planning comprise the process of

planning scenarios that satisfy the scientific or operational objectives of the mission and

evaluating the results of the scenarios as they are carried out. The mission analysis and

planning element needs to be started from the beginning of the development process to

insure that the different mission scenarios are evaluated before a final decision can be

made14.

There are four critical functions carried out by the MCC. It must maintain

communications with the spacecraft, determine the state of the spacecraft, generate

command messages for the spacecraft, and archive the telemetry data from the spacecraft.

The MCC is designed in a way such that the physical configuration satisfies the needs of

the space mission. The working area of the MCC usually displays the spacecraft health,

the spacecraft trajectory and ground tracks, the operational status of the ground stations,

computer simulations of the major and critical subsystems, and terminals for supporting

data processing10.

There has to be a communications network in place for the remote stations to be

able to send data to the MCC. A failure in the network would result in the loss of

spacecraft control. The communication network may be required to handle voice, video,

or data circuits10.

2.3.2 Ground Systems

The ground stations are an important part of a space mission. The following is a

list of tasks the ground stations are responsible for4:

1. Tracking the position of the satellite

2. Telemetry operations to acquire and record satellite status

21

3. Commanding operations to query and control the various functions of the

satellite

4. Controlling operations to schedule all satellite maneuvers, determine orbital

parameters and monitor the on-board computer

5. Processing the data from the satellite

6. Communication links to other ground stations and the MCC

The ground station system comprises of four components: hardware, software,

personnel, and operations4.

The hardware needed for ground stations consists of antennas, a transceiver, data

recorders, computers, and control consoles. The antenna is the most important part of the

hardware because if the antenna is not capable of working to the specified standards then

data cannot be received or transmitted from the ground station. Deciding on the right

antenna to use is difficult, but the approximate diameter needed may be found using the

following equation4:

pc tb

fdD ×××= 3106 (2.7)

where D is the antenna diameter (m), d is the satellite range (km), fc is the carrier

frequency (Hz), b is the telemetry bits rate (bit/sec), and tp is the satellite transmitter

power (W).

There are four types of software the ground station must be able to control. The

four types of software are pre-pass, real-time, post-pass, and on-board. Pre-pass software

is used before the satellite comes into view of the ground station. This software enables

systems to be ready the moment the satellite enters the ground stations viewing area.

Real-time software is used for the communication with the satellite while it is in the

22

viewing area. The software downloads the necessary data and uploads any commands or

data from the ground that is required during the pass of the ground station. Post-past

software is used after the satellite passes the ground station. The software analyzes the

data that was received and stores it for future use. The onboard software is used by the

satellite to store basic commands and safe mode operations which must be programmed

before launch as Read-Only Memory (ROM) as well as more sophisticated commands

which may be uploaded during periods when the satellite is visible to the ground station

and stored in Random-Access Memory (RAM)4.

The ground station also needs people to run the operations of the satellite. There

may be as many as 250 people required at the ground station the first few months after

deployment of a small satellite. The number of people may decrease after the first few

months.4

Modeling the number of ground stations required is often difficult without

specific requirements given by the mission. Time required to transmit data, orbital

altitude, and geographical limitations all affect the number and placement of ground

stations.

2.4 Political, Legal, and Environmental Issues

2.4.1 Political And Legal Issues

An important aspect of spacecraft design which must be considered is how the

government and political bodies will view the design project and either support or bar its

progress. Governments are not always inclined to support programs which will directly

compete with their own. To better understand how the political and legal system

23

interacts with the spacecraft design process we must determine how to model the

interaction between the project and the political and legislative bodies which govern.

Many of the “rules” for space flight have not been set down in law, but rather in

international policy statements or treaties which serve as a guideline for governments in

their dealings with such ventures14. The goal of this portion of the report is to describe

how some of these treaties and policies affect the design process.

Spacecraft designers must understand what aspects of this project will be of

concern to national and international policy makers. A particular aspect of the design

may be of interest to both national and international policy makers, and their policies may

disagree. In the case where there is only one body interested, or where there is

international agreement, the course of action is clear if one wishes to avoid conflict.

However, in areas where national and international policies disagree one must observe

the ruling which is of more recent standing14. For instance, a ruling in 1972 would

supercede a ruling on the same subject from 1967.

2.4.2 Environmental Issues

Environmental issues in space revolve around the concept of a “global commons,”

areas accessible by man but which are outside the jurisdiction of any nation14. Some

examples of such “global commons” are international waterways, the upper atmosphere,

and Antarctica. Although outer space is largely considered to fall into the category of a

global commons, US space policy documents do not specifically list it as such. Because

the US space policy is not clearly defined, the presiding policy is often derived from

Article IX of the Outer Space Treaty9 which provides for international protection of the

outer space environment.

24

The type of mission to be flown is often the determining factor in how long the

mission will take to receive approval. If the same or a similar mission has been flown in

the past, approval may be very quick in coming. If the mission is unlike anything

previously flown, the government often takes more interest in its environmental impact.

For missions flown by the US government, the agency responsible for the mission must

make an assessment of its environmental impact. For missions flown out of the US by

private or commercial sponsors, the Department of Transportation (DOT) may require an

environmental impact assessment under its mandate from the Commercial Launch Act2.

An assessment typically applies to:

- Spacecraft development projects in space science and in space and terrestrial

applications

- Specific experimental projects in space and energy technology

- Development and operations of new space transportation systems

- Advanced development of new space transportation and spacecraft systems

This assessment is used to determine whether an environmental impact statement is

necessary. An environmental impact statement is typically required only if the actions of

the project is expected to have a significant impact on the quality of the human

environment.

2.5 Subsystem Interaction Modeling

The matrix shown in Table 2.1 describes the interaction between the 7 sections of

our subsystem (cost modeling, reliability, mission operations, ground systems, political,

economical and legal issues) and the 12 different disciplines involved in the whole

25

project (astrodynamics, mission analysis, mission geometry, guidance and navigation,

ADCS, communications, command and data handling, power, thermal, space

environment, structures and mechanisms, and launch vehicle selection). The sections are

listed vertically and the disciplines horizontally. The strength of the interaction between

two elements (a section and a discipline) is characterized using coefficients. Those

coefficients are chosen according to the following scale:

- 1: very weak interaction

- 2: weak interaction

- 3: strong interaction

Table 2.8 – Element Interaction Matrix Other Disciplines

Team 5 Elements Astrodynamics Mission Analysis Mission Geometry Guid & Nav ADCS CommCost Modeling 1 1 1 1 1 1

Reliability 1 1 1 1 1 1 Mission Ops 2 2 2 2 2 2

Ground Systems 2 2 2 2 2 3 Economic Issues 1 1 1 1 1 1 Political Issues 1 1 1 1 1 1 Legal Issues 1 1 1 1 1 1

CDH Power Structures & Mechanisms Environment Thermal LV

Cost Modeling 1 1 1 1 1 3 Reliability 1 2 2 2 2 2

Mission Ops 2 1 1 1 1 2 Ground Systems 3 1 1 1 1 2 Economic Issues 1 1 1 1 1 3 Political Issues 1 1 1 1 1 2 Legal Issues 1 1 1 1 1 2

The first conclusion that can be drawn from such a table concerns the interaction

between a section and all the disciplines. For example, the mission operation section is

clearly the most interactive section of our subsystem. If we compute the sum of all the

coefficients relative to this section, they sum to a total of 33. Therefore the mission

26

operation section has mainly strong interactions with every discipline. On the contrary,

economical, political and legal issues have some weak interaction with almost all the

disciplines. This relationship is confirmed when the sum of the coefficients is computed.

It totals 14 for both economical and political issues sections and 13 for the legal issues

section. The only discipline those three sections interact significantly with is the launch

vehicle selection discipline. Almost everywhere else, coefficients are 1’s. The most

demanding sections will be those that require interactions with several disciplines. The

members of these sections will have to collect and share information with many persons

from different disciplines.

We have seen that this interaction matrix has many advantages. It helps

establishing a plan of action, and particularly sets the basic meeting requirements

between actors of both the discipline team and the subsystem section. It also gives one an

idea of how the decisions taken by a subsystem section influence the design project as a

whole.

2.6 Summary and Overview

This chapter is dedicated to the description of the modeling of each section of the

mission support team. The program management team sets up a schedule for the whole

project as well as informational meetings. During those meetings, the program

management team records the progress, problems, lessons and plan of action of each

subsystem. The program management also reports the project history to the customer,

whether government or private. The method of parametric cost estimation and its ability

to apply to any project is described. We also demonstrate how reliability modeling

27

involves design margins, simplification, and redundancies used to improve the overall

reliability of a system.

The mission operations section is composed of four elements: mission analysis

and planning, the MCC, remote TT&C stations and the communications network

between the MCC and the remote stations. Modeling ground systems is described in

detail by splitting up the ground systems into four components: the hardware, the

software, the people, and the operations of the ground station. The hardware is composed

of the antenna and support equipment for each ground station. The four types of software

needed by the ground station are pre-pass, real-time, post-pass, and on-board. The

number of people involved in a ground station and location of ground stations may vary

throughout the lifetime of the mission. The report describes how national and

international space treaties must be considered and respected and how national policy

largely governs environmental issues in space. Finally it is demonstrated how each

subsystem influences the project as a whole as illustrated by the interaction matrix. The

next chapter is devoted to examples of previous designs, their cost analysis, and decisions

on the mission operations and ground stations.

28

CHAPTER 3 – MISSION SUPPORT EXAMPLES

In this chapter examples of the tasks performed and problems encountered by the

mission support team are described. These include the process of cost modeling,

examples of how component reliability may have far-reaching effect, and how to

establish the ground station segment of the mission. Because historical data is not always

readily available to the public some of the examples are theoretical in nature and are

intended to show the methodology in approaching and solving design problems, whereas

other examples are historical and show what precedence has been set by previous space

missions.

3.1 Cost Modeling

Historic examples of cost modeling demonstrate how important an accurate model

can be to the success of the overall mission. Overestimation of the mission cost may

make government or private sector contributors wary, whereas under estimating the

overall cost may lead to budget overruns and perhaps cancellation of the project. We

must therefore note the accuracy of whatever model is chosen to evaluate the project, as

different cost models may produce widely varying estimations.

The Small Satellite Cost Model (SSCM) developed by the Aerospace

Corporation13 differs largely from the parametric cost model used in Ref. 14. For the

High Energy Transient Experiment mission (HETE) built by MIT and AeroAstro, the

SSCM estimates the spacecraft bus cost to be $7.0M13 while Ref. 14 estimates the bus

cost to be $34M, both in FY95$. The actual cost of the mission came to $30.1M, while

the spacecraft bus cost was only $5.6M. Both models were inaccurate, but the model in

29

Ref. 14 overestimated the bus cost by approximately 510%. For the Clementine mission

designed by Naval Research Labs (NRL), Ref. 14 estimated the bus cost to be $59M

while the SSCM estimated the cost to be $22.7M13. The actual cost of the spacecraft bus

was $52.0M. In this instance, the model from Ref. 14 was fairly accurate, but the SSCM

model was off by 130%. To determine which model is applicable for which situation,

one must examine the historical data used to build the model. The SSCM model was not

created using any information from spacecraft with masses over 400 kg, or from any

interplanetary spacecraft. The model used in Ref. 14 was developed using spacecraft

with masses under 400 kg, but included a wider variety of missions and developmental

methods.

Cost modeling is also used to estimate the support cost of missions, and can be

critical in determining how expensive a mission will be to maintain. The Hubble Space

Telescope (HST) has required several servicing missions already, and a cost analysis was

performed on each of those missions. Servicing Mission 3A was to replace several parts,

including gyroscopes, guidance equipment, and the on-board computer. It also required

that the equipment aboard the shuttle used to service HST be transferred from the aging

Colombia to the Discovery. The total cost of hardware, software, and flight changes was

estimated to be $95.0M5. In addition, the cost of the shuttle launch itself came to $110M

for a total of $205M for Servicing Mission 3A only5. This cost must be initially

incorporated into the overall cost of the mission to create an accurate cost model.

An example of how to progress through a cost model step by step can be found in

Ref. 14, which uses FireSat, a small satellite in LEO designed to detect forest fires, as a

running example throughout the book. Chapter 20 in Ref. 14 details the parametric cost

30

process and uses FireSat as an example of how to apply the parametric cost modeling

process.

The first step in applying the parametric cost model is to define the cost elements

that are used in the CERs. For FireSat these include all of the components listed in Table

2.3. These cost elements are standard for the process described in Ref. 14. Table 3.1 lists

the cost for each component, applying the process outlined in Table 2.3 for a traditional

satellite design method. As shown in Ref. 14, there are large discrepancies between the

traditional satellite design model and the small satellite design model, mostly in the

RDT&E and TFU costs of the satellite payload. This report uses the costs as determined

using the traditional, large satellite design model.

We then use the estimated 100 KLOC in Ada and Tables 20-10 and 20-11 in Ref.

14 to computer the additional development costs as shown in Table 3.2. The 5-year life

in orbit and the estimated 10 contractor personnel required can be used to estimate the

total operations and maintenance cost per year, as shown in Table 3.3. The total costs are

then summarized in Table 3.4.

31

Table 3.1 – FireSat Costs for RDT&E and TFU Adapted from Ref. 14

Cost Component Parameter RDT&E Cost (FY00$K)

TFU Costs (FY00$K)

SE ($K)

1. Payload 1.1 IR Sensor Aperture dia. =

0.264 m 168,462 67,386 94,265

2. Spacecraft bus 2.1 Structure Mass = 32.0 kg 2,784 419 1,368 2.2 Thermal Mass = 6.8 kg 1,337 197 830 2.3 Electrical Power

System (EPS) Mass = 45.7 kg 2,862 2,06 3,360

2.4a Telemetry Tracking & Command and Data Handling(TT&C)

Mass = 6.8 kg 2,356 1,894 2,819

2.5 ADCS Mass = 18.3 kg 5,753 2,799 4,570

2.6 Propulsion N/A

3. Integration, Assembly, & Test (IA&T)

Bus + Payload RDT&E Costs = $183,554

40,453 1,456 19,826

4. Program Level $183,554 52,450 25,494 37,773 5. Ground Support

Equipment $183,554 22,184 - 7,543

6. Launch & Orbital Operations Support (LOOS)

Spacecraft + payload mass = 140 kg

- 686 547

7. Flight Software 26 KLOC 5,655 0 - Total Space Segment Cost to Contractor

304,297 102,398 -

10% Contractor Fee 30,430 10,240 - Total Space Segment Cost to Government

334,727 112,638 -

8. Launch Segment Pegasus XL Launchers

- 13,000 -

Total Cost of Deployment 574,738 136,947

32

Table 3.2 - FireSat Ground Segment and Operations Costs in FY00$M Adapted from Ref. 14

Development CostSoftware 100 KLOC (Ada) @ $220/LOC 22.0 Equipment 17.8 Facilities 4.0

Subtotal 43.8 Management 4.0 Systems Engineering 6.6 Product Assurance 3.3 Integration and Test 5.3 Logistics 3.3

Total 66.3

Table 3.3 - FireSat Annual Operations and Maintenance Cost in FY00$M Adapted from Ref. 14

Operations and Maintenance 10 Contractor Personnel ($160K/yr) including fee 1.6 Maintenance 4.4 Total Annual Cost 6

Table 3.4 - FireSat Life-Cycle Cost Estimate in FY00$M Adapted from reference 14

Initial Deployment Cost Space Segment – SMAD Table 20-17 548.7Launch Segment – SMAD Table 20-17 26.0 Ground Segment – SMAD Table 20-20 66.3 Subtotal 641.0Operations and Maintenance – SMAD Table 20-19 Annual Ops. and Maintenance 6.0 Total Ops. and Maintenance for 5 years 30.0

Total Life-Cycle Cost for 5 years 671.0

3.2 Reliability

The reliability modeling section showed that reliability is sometimes approached

as a variation on a risk or failure analysis. A good example of such a risk analysis is the

33

Cassini Space Mission. This spacecraft, launched on October 15, 1997, was designed to

orbit Saturn and return data regarding the planet’s environment and about one of its

moons, Titan. Solar arrays were not feasible power sources for the spacecraft because of

Saturn's distance from the Sun. The Cassini orbiter therefore generates power using three

radioisotope thermoelectric generators (RTGs), which use heat from the natural decay of

plutonium to generate electricity. At the end of the 11-year Cassini mission, they will still

be capable of producing at least 628 watts1. However, using this type of power system is

not without risks. If the launch vehicle happened to fail or if the spacecraft could not

execute its Earth flyby properly, radioactive material could be sprayed into the

atmosphere and contaminate the human population. Therefore NASA ran an accident

analysis to estimate the risks of RTG failure and exposure to radioactive material. In the

unlikely event that Cassini reentered Earth’s atmosphere some plutonium dioxide could

be released. The radiation dose that a person would be expected to receive is less than

one millirem total over 50 years, which is expected to cause about 2,300 cases of cancer

worldwide. However, an independent study7 demonstrated that the NASA estimations are

too low and their assumptions too broad, and need refinement. According to this study

the number of cancer cases would be higher by a factor of at least 100.

NASA has established a set of reliability guidelines that have proven their

effectiveness on previous missions and should therefore be followed to design the most

reliable space systems8. Classical reliability practice is generally associated with

minimizing catastrophic failures of parts. Of equal importance, however, is assuring that

the desired essential mission controls and scientific measurements are made with the

intended accuracy, fidelity, and stability. To this end, a uniform, disciplined, systematic

34

approach to performance design verification is essential. Uniformity is achieved by use of

a common part variation database by all analysts on a specific project. Discipline is

achieved by a common analysis containing qualitative and quantitative circuit

performance attributes that are traceable to the assembly, subsystem and system

requirements. A stated or implied level of statistical confidence is required, which results

from the use of either an Extreme Value Analysis (EVA)8 or a Root Sum Squared (RSS)8

approach to the circuit performance variation at some statistical level, usually two or

three times the standard deviation (σ). Another statistical approach is the Monte Carlo

method of repeated trials with randomly selected combinations of part variations.8

3.3 Ground Stations

Determining the type and number of ground stations depends on the mission of

the spacecraft. For interplanetary missions, the type of ground stations is already clearly

defined, but there are several options that could be used for missions that orbit the Earth.

Interplanetary missions use NASA’s Deep Space Network (DSN) for the

communications between Earth and the spacecraft. The DSN consists of the three deep-

space facilities located on different continents of the world. These facilities then send the

received data to the operational facility at NASA’s Jet Propulsion Laboratory (JPL). The

data are sent from JPL to the command group that is responsible for the mission.15

Examples of missions that have used DSN for communication are Deep Space 1, Cassini,

and the Mars Global Surveyor.11

Space missions that need to have constant communication with the command

center may use the Tracking Data and Relay Satellite System (TDRS). The TDRS

35

network is comprised of three satellites in geosynchronous orbit. The TDRS satellites

allow for spacecraft to send data to the TRDS satellites which will then send the data to

the TDRS network ground station at the White Sands Ground Terminal in White Sands,

New Mexico. The data can then be sent to the control center for the space mission.

Examples of space missions that use the TDRS system for communication are the

International Space Station, and all of the Shuttle missions. The command centers for

these missions is located at Johnson Space Center (JSC) in Houston, Texas.3

Using the TDRS network is expensive, and therefore programs that do not have

money to spend on TDRS use multiple ground stations located in the world. These space

missions have one command center to which all of the data is sent to, but the data comes

from many different ground stations. One example of this is the LANDSAT 7 mission.

LANDSAT 7 takes pictures of the Earth’s surface and sends the information to the

ground stations. LANDSAT 7 takes more pictures than it can store in its onboard data

storage system, so it must send the pictures to ground stations often. The need to

download pictures often requires there to be many ground stations that can handle the

pictures and then send to the LANDSAT 7 control center. There are 20 ground stations

that LANDSAT 7 can send pictures to. Once the pictures are received they are sent to the

US Geological Survey's EROS Data Center in Sioux Falls, South Dakota.12

Other space missions that do not need to download a lot of data use a limited

number ground stations. The Ionospheric Observation Nanosat Formation mission,

involving the University of Washington, Utah Sate University, and Virginia Tech, uses

two ground stations located on the campuses of Utah State University and Virginia Tech.

When the three satellites are over the ground stations, information can be downloaded

36

and then sent to the main computer that will store and process data for the mission. These

conditions are all that this mission requires for data download and meets the constraint set

by the limited amount funds available for the project.6

37

CHAPTER 4 – SUMMARY AND CONCLUSIONS

This report has focused on the mission support portion of any space flight project,

but has focused in some places on the needs of a space based tether launch system.

Information regarding program management, cost modeling, reliability, mission

operations and ground support, and economic, political, and legal issues has been

discussed in a way which will allow for the reader to make practical observations and use

of the information, so long as an in-depth knowledge is not required. This chapter

presents a summary and draws some helpful conclusions of each of these subjects.

4.1 – Program Management

The success of the program management team is critical to the success of the

overall mission. Their duties, including running group meetings, maintaining a schedule

of action items and due dates, reporting progress to the customer, and maintaining a

cohesive group, are the backbone of any project14. If the program management team fails

in these duties the project will not be a success despite whatever technical progress is

made. Tools such as Gant charts and work breakdown structures help the program

management team illustrate to the rest of the group their progress along with the

projected or expected progress. This type of external monitoring helps to keep the group

in focus and driven toward their goals. In a non-academic setting, the program

management team is critical in establishing a cost breakdown structure and monitoring

the cost-to-date of the project, along with the projected costs till completion. Monitoring

of these costs is critical for any project and will allow for better relationships with the

project team and the funding body or agency.

38

4.2 – Cost Modeling and Reliability

The ability to estimate the cost of a project can be a critical element in its success.

This report provides a simple model, based on historical data, by which the cost of a

small satellite project can be estimated14. These costs can also be scaled somewhat

upward to apply to larger projects. The model presented here is not to be taken as

accurate to the dollar, rather is most useful in comparing the cost of separate options

which have both been analyzed using the same criteria. Within the context of a design

competition, the results of cost modeling allow the design team to justify its results and

provide a historical basis for cost prediction. As shown in section 3.1, the cost of a

project can vary drastically due to unforeseen influences out of the control of the project

team and we should not take the cost predicted by any model as a certainty.

This lack of certainty limits a cost model’s usefulness but does not eliminate its

usefulness. Cost modeling figures prominently in the decision of funding bodies and

agencies to maintain or cancel projects, and helps the project management team decide

how to allocate funding internally as well. Although cost models are not always

accurate13, as the number of missions that reach successful completion continues to

increase the historical data will allow cost modeling to become more accurate in

predicting cost trends. During the course of a project inaccuracies in cost estimation may

become apparent, and will allow the project management team to either adjust their cost

estimation method or to adjust the expenditures of the project accordingly. Without any

form of cost estimation these inconsistencies in the predicted and actual budgets would

remain unseen until either the completion of the project, or until the accounts run empty.

39

Another item that must be accurately predicted for the success of a mission is its

reliability. While random failures in spacecraft systems are not easily predictable, it is

the duty of the designers to identify and eliminate sources of wear-out failure that

jeopardize the success of the mission. Design margins, redundancy, and system

complexity should all be considered when planning for optimum reliability both in a

spacecraft and a single spacecraft system. Design margins allow for an acceptable

amount of error in predicting the conditions under which a system will operate or in the

manufacturing of a component. Another criteria for judging reliability is the complexity

of the system. The advantages gained by adding complexity must be gauged against the

reduced reliability of the system as a whole. Finally, redundancy allows the designers to

improve the reliability of a system be eliminating a single-point fault which would cause

mission failure based on a single component failure. Redundancy may be accomplished

by either adding two identical systems to the spacecraft or by using multiple systems with

different designs to accomplish the same function. This second approach eliminates any

systematic error found in the component in question, but incurs greater costs in time,

manufacturing, and testing.14

The reliability of a system can be quantitatively measured using the basic

equations set forth in section 2.2.2.2. Once a system for predicting the reliability of each

component has been established, the reliability of systems and eventually of the

spacecraft can be described by a quantitative value, typically the chance of failure as a

function of the current lifetime.

40

4.3 – Mission Operations and Ground Support

The mission operations team and the ground stations are also very important parts

of a space mission. The mission operations team evaluates the different mission scenarios

at the beginning of the design process to make sure that the mission objectives are met in

every possible scenario.. They then must determine what communications are necessary

to control the spacecraft from the ground station. The mission operations team uses the

ground station to determine the state of the spacecraft as well as sending commands for

the spacecraft to performed whatever actions are necessary to complete its mission

objectives. Once the spacecraft is launched the mission operations team relocates to the

master control center, through which they communicate with their ground stations located

around the world.

The number and type of ground stations required for a given mission are

determined by the needs and constraints of the mission and spacecraft. There are several

options for the location and type of ground stations that are chosen from based on the

amount and type of data that must be transmitted and the amount of available funding

allocated for ground stations. For missions that require a large volume of data transfer

multiple ground stations may be required around the globe. For other mission which do

not require a large volume of data transfer the use of a single ground station in

conjunction with TDRS may be sufficient to handle all communications.

4.4 – Summary

While the mission support team is often not considered a core part of the

engineering process in spacecraft design, their role in designing the mission makes them

41

a vital portion of the design process. Project management, cost and reliability modeling,

mission operations, and ground support are all elements that support and allow the

technical objectives of the mission to succeed by providing support for the technical

program in the form of guidance, scheduling, budgeting, and by acting as liaison between

the design team and the customer. This support is critical in taking a design concept from

the drawing board and into production.

42

REFERENCES

1. Cassini-Huygens Mission to Saturn and Titan website, Last update: 19 October 2001, Accessed: 22 October 2001, Available at: http://www.jpl.nasa.gov/cassini/

2. Commercial Space Act of 1998, Library of Congress Website – 105th Congress

Archives. Accessed October 7, 2001. Available at: http://thomas.loc.gov/home/r107query.html

3. Dumoulin, J., “NSTS Shuttle Reference Manual” Kennedy Space Center,

Updated 31 August 2001. Available at: http://science.ksc.nasa.gov/shuttle/ technology/sts-newsref/sts-jsc-comm.html#sts-tdrss

4. Fortescue, Peter and Stark, John (editors), Spacecraft Systems Engineering, 2nd

Edition, December 1999, John Wiley & Sons Ltd., New York, NY

5. Hubble Facts, NASA Goddard Space Flight Center Website. Accessed: 23 October 2001. Available at: http://sm3a.gsfc.nasa.gov/downloads/sm3a_fact_ sheets/cost-to-taxpayers.pdf

6. ION-F Critical Design Review. Tempe, Arizona. April 5, 2001. Slide 310 7. Kaku, M., Accident Risks from the Cassini Space Mission, Accessed: 21 October

2001, Available at: http://southmovement.alphalink.com.au/antiwar/kaku.htm#6 8. NASA Reliability and Maintainability Steering Committee, NASA RELIABILITY

PREFERRED PRACTICES FOR DESIGN AND TEST, Last update: February 1999, Accessed: 22 October 2001, Available at: http://www.hq.nasa.gov/office/codeq/relpract/prcls23.htm

9. Outer Space Treaty, Department of State Web Archives. Updated January 20,

2001. Accessed September 20, 2001. Available at: http://www.state.gov/www/global/arms/treaties/space1.html

10. Pisacane, V. L. and Moore, R. C. (editors), Fundamentals of Space Systems, 1994,

Oxford University Press, Oxford England 11. Reichley, S., “JPL Missions”, Jet Propulsion Laboratory, California Institute of

Technology, Accessed 29 October 2001. Available at: http://www.jpl.nasa.gov/missions/missions_index.html

12. Web, E., “LANDSAT 7”, U.S. Department of the Interior and U.S. Geological

Survey, Accessed 30 October 2001. Available at: http://landsat7.usgs.gov

13. Wertz, J. R. and Larson, W. J. (editors), Reducing Space Mission Cost, 1996, Microcosm Inc., El Segundo California

http://www.jpl.nasa.gov/cassini/http://thomas.loc.gov/home/r107query.htmlhttp://science.ksc.nasa.gov/shuttle/http://southmovement.alphalink.com.au/antiwar/kaku.htm#6http://www.state.gov/www/global/arms/treaties/space1.htmlhttp://www.jpl.nasa.gov/missions/missions_index.htmlhttp://landsat7.usgs.gov/

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14. Wertz, J.R. and Larson, W.J. (editors), Space Mission Analysis and Design, 3rd Edition, 1999, Microcosm Inc., El Segundo California

15. Wolff, S., “Deep Space Network”, Jet Propulsion Laboratory, California Institute

of Technology, Updated 29 October 2001 Available at: http://deepspace.jpl.nasa.gov/dsn/index.html

List of TablesList of FiguresFigure 1.1 – Lightweight matrix organization1AbbreviationsList of SymbolsChapter 1 – Introduction1.1 Elements of Mission Support1.1.1 Program Management1.1.2 Cost Modeling and Reliability1.1.3 Mission Operations And Ground Systems1.1.4 Economic, Political, and Legal Issues

1.2 Summary and Overview

Chapter 2 – Subsystem Modeling2.1 Program Management2.2 Cost and Reliability Modeling2.2.1 Cost Modeling2.2.2.1 Space Segment CostsCost ComponentFACTORS FOR OTHER LANGUAGES

2.2.2 Reliability Modeling2.2.2.1 Failures2.2.2.2 Equations

2.3 Mission Operations and Ground Systems2.3.1 Mission Operations2.3.2 Ground Systems

2.4 Political, Legal, and Environmental Issues2.4.1 Political And Legal Issues2.4.2 Environmental Issues

2.5 Subsystem Interaction Modeling2.6 Summary and Overview

Chapter 3 – Mission Support Examples3.1 Cost ModelingCost ComponentOperations and Maintenance

Subtotal

3.2 Reliability3.3 Ground Stations

Chapter 4 – Summary and Conclusions4.1 – Program Management4.2 – Cost Modeling and Reliability4.3 – Mission Operations and Ground Support4.4 – Summary

References