Space Engineering 2 © Dr. X Wu, 2012 1 Space Engineering 2 Lecture 3

Space Engineering 2 © Dr. X Wu, 20121

Space Engineering 2

Lecture 3

Group Presentations

Week 5: mission design (5%) Week 13: spacecraft bus subsystem

design (5%)


Outline

Introduction Systems Engineering Spacecraft Environment Spacecraft Bus Subsystems


What is a Space System Ground

Spaceflight Operations Payload Operations Payload Data Processing

Space Orbits Spacecraft

Launch Launch Vehicle Integration Launch Operations


Spacecraft Subsystems

Space Segment

Payload Bus

Structure

Mechanisms

Attitude and orbit control

Thermal Propulsion

Power Telemetry and command

Data handling

Space Mission Elements


Systems Engineering A logical process for system development Functional & physical decomposition of system into logical

parts Involves development of system requirements:

System Analysis Requirements Development Interface Requirements

Requirements Validation Test & Demonstration Simulation Analysis

Physical/functional configuration audits Integration & Test Planning “Cradle to Grave” lifecycle planning

Treaty provisions and DoD regulations require disposal of satellites at the end of life.


Roles of Systems Engineering

Develop the system architecture Develop and maintain the requirements Analyze and characterize the system design Manage technical resources and

performance Develop and maintain interfaces Verify and validate the system Identify, assess, manage and mitigate risks

during design, development and implementation

Organize technical peer reviews


Spacecraft Systems Engineering Process in SMAD

Analyze the mission Mission objectives Estimation of needs, requirements, and constraints

Characterize the mission Alternative mission concepts Alternative mission architecture System drivers Characterizing the mission architecture

Evaluate the mission Identification of critical requirements Mission utility Mission concept selection

Define requirements


Objectives, Requirements and Constraints

Mission objectives Primary objectives: the broad goals that the

system must achieve to be productive Secondary objectives: for political, social, or

cultural purposes Requirements and constrains

Functional requirements define how well the system must perform to meet its objectives

Operational requirements determines how the system operates and how users interact with it

Constraints limit cost, schedule and implementation techniques


Mission Concepts Data Delivery – how mission and housekeeping data are obtained,

distributed and used Space vs. ground Central vs. distributed processing Level of autonomy

Communications Architecture – how the subsystems talk to each other and the ground station

Intra-satellite link Inter-satellite link Down/Up link

Tasking, Scheduling, and Control – how the system decides what to do in the lifetime

Spacecraft autonomy Mission lifetime – the overall time from planning, building,

deployment, operations, replacement, and end-of-life Mission Concept Selection

Go/no-go decision on proceeding with the mission Selection of the mission concept Detailed engineering decisions


Identifying Alternative Mission Architecture

A. Identify the mission elements subject to trade

B. Identify the main options for each tradable elements

C. Construct a trade tree of available optionsD. Prune the trade tree by eliminating

unrealistic combinationsE. Look for other alternatives which could

substantially influence how we do the mission


Identifying System Drivers

Identify the area of interest Identify parameters which measure

the area of interest Develop first-order algorithms like time

delay, resolution… Examine the factors Look for ‘hidden drivers’

Develop a more accurate algorithm to estimate the parameters


Characterizing the Mission Architecture

A. Define the preliminary mission conceptB. Define the subject characteristicsC. Determine the orbit or constellation characteristicsD. Determine payload size and performanceE. Select the mission operations approachF. Design the spacecraft busG. Select a launch and orbit transfer systemH. Determine deployment, logistics, and end-of-life

strategiesI. Provide costing supportJ. Document and iterate


Critical Requirements

Requirement What if affects

Coverage or response time

Number of satellites, altitude, inclination, communications architecture, payload field of view, scheduling, staffing

Resolution Instrument size, altitude, attitude control

Sensitivity Payload size, complexity; processing, and thermal control; altitude

Mapping Accuracy Attitude control, orbit and attitude knowledge, mechanical alignments, payload precision, processing

Transmit power Payload size and power, altitude, inter-satellite distance

On-orbit lifetime Redundancy, weight, power and propulsion budgets, component selection

Survivability Altitude, weight, power, component selection, design of space and ground system, number of satellites, number of ground stations, communications architecture


Mission Utility

Provide quantitative information for decision making

Provide feedback on the system design

Mission simulation Commercial mission analysis and

mission utility tools

Mission Concept Selection

Overall mission objectives Technical feasibility Level of risk Schedule and budget Preliminary results


Requirements Specification

Purpose The contract between the builder and the user Define capabilities, without necessarily defining

implementation Define constraints

Characteristics Unambiguous Complete Consistent Verifiable and testable Limit bias towards a particular implementation


Content of Requirements Document

Define context of the system How will the system be used? Who/What

is involved

Functional requirements What is the system supposed to do?

Performance specs Definitions/glossary Non functional requirements

Non-functional Requirements



System Resources

System level Mass Power Energy Volume Communication

Subsystem level CPU utilization On-board storage Switch (power

feed) availability Data interface

availability Fuel capacity


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 Design Elements 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


System Integration and Test Types:

Functional testing Do subsystems work together? “Fit” check payload fairing, adapter

Environmental testing Thermal vacuum, shock and vibration testing

Combined functional and environmental testing Usually spacecraft level thermal vacuum involved integrated

functional testing Final System demo: Do all segments work together, mainly

ground and space Payload or system characterization

Performance can be altered by the space environment Often performed in thermal vacuum chamber

Can Use a combination of “hardware in loop” and simulation:

Ground Testing Systems like propulsion and attitude control cannot be

operated safely on the ground May use “stimulators” for sensors like sun & earth sensor, or

star tracker.


Design Verification and Qualification Testing

Design Verification Validate design precepts and models Examine system limitations Build & Test, Build & Test…

Qualification: Determine system suitability for mission Provides tool for customer to measure success

of the enterprise Allows time for fixes to meet requirements – may

involve warranty period


Types of Design Tests

Functional “Life” Testing (could involve structural, thermal,

illumination, power cycling, radiation exposure etc.) Component to System Level Often performed in between other forms of test

Structural Static Tests Dynamic Tests

Thermal Thermal cycling Thermal vacuum

Conclusion

Spacecraft systems engineering envisioning, designing, building, operating,

and funding space systems.

Life cycle of a project From mission concept to orbit

Supporting documentation Requirements specification Design documents Interface control documents


Documents

Space Engineering 2 © Dr. X Wu, 2012 1 Space Engineering 2 Lecture 3