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

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

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

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

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

Space Mission Elements

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

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

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

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

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

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

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

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

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

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

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 Space Engineering 2 © Dr. X Wu, 2008

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

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

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

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

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

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

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

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

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

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