Space Engineering 2 © Dr. X Wu, 20081

Space Engineering 2

Lecture 1

Group Presentations

Week 5: preliminary design review / mission design (5%)

Week 13: critical design review / spacecraft bus subsystem design (5%)

Space Engineering 2 © Dr. X Wu, 20083

Outline

Introduction Systems Engineering Spacecraft Environment Spacecraft Bus Subsystems

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What is a Space System Ground

Spaceflight Operations Payload Operations Payload Data Processing

Space Orbits Spacecraft

Launch Launch Vehicle Integration Launch Operations

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Ground

Ground Activities: Spacecraft Flight

Operations Payload Operations Payload Data Processing Payload Data

Dissemination

Facilitated By: Real-Time Processing Payload Dissemination

Infrastructure Powerful Payload

Processing Facilities Mission Simulations

Can BeMerged

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Launch

Selection: Enough “throw weight” Enough “cube” (volume) Acceptable ride Good record…

Integration: Launch loads imparted

to spacecraft Mechanical/Electrical

Integration

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Space Mission Architecture

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Payloads and MissionsMission Trajectory type

Communications Geostationary for low latitudes, Molniya and Tundra for high latitudes (mainly Russian), Constellation of polar LEO satellites for global coverage

Earth Resources Polar LEO for global coverage

Weather Polar LEO, or geostationary

Navigation Inclined MEO for global coverage

Astronomy LEO, HEO, GEO and ‘orbits’ around Lagrange points

Space Environment Various

Military Various, but mainly Polar LEO for global coverage

Space Stations LEO

Technology Demonstration Various

Note: GEO – Geostationary Earth Orbit; HEO – Highly Elliptical Orbit; LEO – Low Earth Orbit; MEO – Medium height Earth Orbit

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Objectives and Requirements of a Space Mission

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Space System Development All systems development start with a “mission need” (the

Why) Then mission requirements are developed to meet this need

(the What) often along with a concept of operations Note: Often we make the mistake of putting “the

How” in the Mission Requirement From 1 and 2 above develop derived requirements for (the

How): Space

Mission orbit Payload Types (Communications, remote sensing, data relay) Spacecraft Design

Ground Facilities and locations Computers/Software Personnel/Training

Launch segments Note: The requirements generation process is often iterative

and involves compromises

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Requirements of a Spacecraft1. The payload must be pointed in the correct

direction2. The payload must be operable3. The data from the payload must be communicated

to the ground4. The desired orbit for the mission must be

maintained5. The payload must be held together, and on to the

platform on which it is mounted6. The payload must operate and be reliable over

some specified period7. All energy resource must be provided to enable the

above functions to be performed

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Spacecraft Subsystems

Space Segment

Payload Bus

Structure

Mechanisms

Attitude and orbit control

Thermal Propulsion

Power Telemetry and command

Data handling

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Spacecraft Description

Spacecraft have two main parts: Mission Payload Spacecraft Bus

Mission Payload A subsystem of the spacecraft that performs the actual mission

(communications, remote sensing etc.) All hardware, software, tele- communications of payload data

and/or telemetry and command There can be secondary payloads

Spacecraft Bus Hardware & software designed to support the Mission Payload

Provides Power Temperature control Structural support Guidance, Navigation & Control

May provide for telemetry and command control for the payload as well as the vehicle bus

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Spacecraft Development Process

Some types: Waterfall (sequential) Spiral (iterative)

Basic Sequence:

1. Conceptual design

2. Detailed design

3. Develop detailed engineering models

4. Start production

5. Field system

6. Maintain until decommissioned DoD mandates integrated, iterative

product development process

RequirementsDevelopment

DetailedDesign

EngineeringDevelopment

&Production

Field(IOC)

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Serial (waterfall) Development1. Traditional “waterfall” development

process follows logical sequence from requirements analysis to operations.

2. Is generally the only way to develop very large scale systems like weapons, aircraft and spacecraft.

3. Allows full application of systems engineering from component levels through system levels.

4. Suffers from several disadvantages:• Obsolescence of technology (and

sometimes need!)• Lack of customer

involvement/feedback• Difficult to adjust design as program

proceeds

http://www.csse.monash.edu.au/~jonmc/CSE2305/Topics/07.13.SWEng1/html/text.html

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Spiral Development

From: http://www.maxwideman.com/papers/linearity/spiral.htmAnd Barry Boehm, A Spiral Model of Software Development and Enhancement, IEEE Computer, 1988

Software Development Centric Example

Good features1. In this approach, the entire application is built

working with the user. 2. Any gaps in requirements are identified as work

progresses into more detail. 3. The process is continued until the code is finally

accepted. 4. The spiral does convey very clearly the cyclic

nature of the process and the project life span.

Not so good features1. This approach requires serious discipline on the

part of the users. The user must provide meaningful realistic feedback.

2. The users are often not responsible for the schedule and budget so control can be difficult.

3. The model depicts four cycles. How many is enough to get the product right?

4. It may be cost prohibitive to “tweak” the product forever.

Simply put: Build a little – Test a little!

Can this work for every type of project?

System Development Process

‘Breadboard’ system Concept development and proof of concept

Prototype First draft of complete system Implements all requirements

Engineering model Complete system without final flight configuration Plug and play with flight model

Flight model The final product Space-ready product, implements all requirements

Design Review

Preliminary Design Review (PDR) Architecture and interface specifications Software design Development, integration, verification test plans Breadboard

Critical Design Review (CDR) System Architecture Mechanical Design Elements Electrical Design Elements Software Design Elements Integration Plan Verification and Test Plan Project Management Plan

Spacecraft Integration and Test

Methodical process for test of spacecraft to validate requirements at all levels

Sequence:1. Perform component or unit level tests2. Integrate components/units into subsystems3. Perform subsystem tests4. Integrate subsystems into spacecraft5. Perform spacecraft level test6. Integrate spacecraft into system7. Perform system test when practical