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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%)
Space Engineering 2 © Dr. X Wu, 20083
Outline
Introduction Systems Engineering Spacecraft Environment Spacecraft Bus Subsystems
Space Engineering 2 © Dr. X Wu, 20084
What is a Space System Ground
Spaceflight Operations Payload Operations Payload Data Processing
Space Orbits Spacecraft
Launch Launch Vehicle Integration Launch Operations
Space Engineering 2 © Dr. X Wu, 20085
Spacecraft Subsystems
Space Segment
Payload Bus
Structure
Mechanisms
Attitude and orbit control
Thermal Propulsion
Power Telemetry and command
Data handling
Space Mission Elements
Space Engineering 2 © Dr. X Wu, 20087
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.
Space Engineering 2 © Dr. X Wu, 20088
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
Space Engineering 2 © Dr. X Wu, 20089
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
Space Engineering 2 © Dr. X Wu, 200810
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
Space Engineering 2 © Dr. X Wu, 200811
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
Space Engineering 2 © Dr. X Wu, 200812
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
Space Engineering 2 © Dr. X Wu, 200813
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
Space Engineering 2 © Dr. X Wu, 200814
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
Space Engineering 2 © Dr. X Wu, 200815
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
Space Engineering 2 © Dr. X Wu, 200816
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
Space Engineering 2 © Dr. X Wu, 200818
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
Space Engineering 2 © Dr. X Wu, 200819
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
Space Engineering 2 © Dr. X Wu, 200820
Space Engineering 2 © Dr. X Wu, 200821
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
Space Engineering 2 © Dr. X Wu, 200822
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
Space Engineering 2 © Dr. X Wu, 200823
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
Space Engineering 2 © Dr. X Wu, 200824
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
Space Engineering 2 © Dr. X Wu, 200825
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.
Space Engineering 2 © Dr. X Wu, 200826
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
Space Engineering 2 © Dr. X Wu, 200827
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
Space Engineering 2 © Dr. X Wu, 200828