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

2. Group Presentations Week 5: mission design (5%)
Week 13: spacecraft bus subsystem design (5%)

3. Space Engineering 2 © Dr. X Wu, 2008
Outline
Introduction
Systems Engineering
Spacecraft Environment
Spacecraft Bus Subsystems
Space Engineering 2 © Dr. X Wu, 2008

4. Space Engineering 2 © Dr. X Wu, 2008
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, 2008

5. Spacecraft Subsystems
Space Segment
Payload
Bus
Structure
Mechanisms
Attitude and orbit control
Thermal
Propulsion
Power
Telemetry and command
Data handling
Space Engineering 2 © Dr. X Wu, 2008

6. Space Mission Elements

7. Space Engineering 2 © Dr. X Wu, 2008
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. 7
Space Engineering 2 © Dr. X Wu, 2008

8. 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 8
Space Engineering 2 © Dr. X Wu, 2008

9. 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, 2008

10. 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 10
Space Engineering 2 © Dr. X Wu, 2008

11. Space Engineering 2 © Dr. X Wu, 2008
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 11
Space Engineering 2 © Dr. X Wu, 2008

12. Identifying Alternative Mission Architecture
Identify the mission elements subject to trade
Identify the main options for each tradable elements
Construct a trade tree of available options
Prune the trade tree by eliminating unrealistic combinations
Look for other alternatives which could substantially influence how we do the mission 12
Space Engineering 2 © Dr. X Wu, 2008

13. 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 13
Space Engineering 2 © Dr. X Wu, 2008

14. Characterizing the Mission Architecture
Define the preliminary mission concept
Define the subject characteristics
Determine the orbit or constellation characteristics
Determine payload size and performance
Select the mission operations approach
Design the spacecraft bus
Select a launch and orbit transfer system
Determine deployment, logistics, and end-of-life strategies
Provide costing support
Document and iterate 14
Space Engineering 2 © Dr. X Wu, 2008

15. Critical Requirements
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, 2008

16. Space Engineering 2 © Dr. X Wu, 2008
Mission Utility
Provide quantitative information for decision making
Provide feedback on the system design
Mission simulation
Commercial mission analysis and mission utility tools
Space Engineering 2 © Dr. X Wu, 2008

17. Mission Concept Selection
Overall mission objectives
Technical feasibility
Level of risk
Schedule and budget
Preliminary results

18. 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, 2008

19. 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
Space Engineering 2 © Dr. X Wu, 2008

20. Non-functional Requirements20
Space Engineering 2 © Dr. X Wu, 2008

21. Space Engineering 2 © Dr. X Wu, 2008
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, 2008

22. 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, 2008

23. Space Engineering 2 © Dr. X Wu, 2008
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, 2008

24. Spacecraft Integration and Test
Methodical process for test of spacecraft to validate requirements at all levels
Sequence:
Perform component or unit level tests
Integrate components/units into subsystems
Perform subsystem tests
Integrate subsystems into spacecraft
Perform spacecraft level test
Integrate spacecraft into system
Perform system test when practical
Space Engineering 2 © Dr. X Wu, 2008

25. 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, 2008

26. Design Verification and Qualification Testing
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, 2008

27. Space Engineering 2 © Dr. X Wu, 2008
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
Space Engineering 2 © Dr. X Wu, 2008

28. Space Engineering 2 © Dr. X Wu, 2008
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, 2008