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

Space Engineering 2 © Dr. X Wu, 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, 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 Be Merged

Space Engineering 2 © Dr. X Wu, Launch  Selection:  Enough “throw weight”  Enough “cube” (volume)  Acceptable ride  Good record…  Integration:  Launch loads imparted to spacecraft  Mechanical/Electrical Integration

Space Engineering 2 © Dr. X Wu, Space Mission Architecture

Space Engineering 2 © Dr. X Wu, Payloads and Missions MissionTrajectory type CommunicationsGeostationary for low latitudes, Molniya and Tundra for high latitudes (mainly Russian), Constellation of polar LEO satellites for global coverage Earth ResourcesPolar LEO for global coverage WeatherPolar LEO, or geostationary NavigationInclined MEO for global coverage AstronomyLEO, HEO, GEO and ‘orbits’ around Lagrange points Space EnvironmentVarious MilitaryVarious, but mainly Polar LEO for global coverage Space StationsLEO Technology DemonstrationVarious Note: GEO – Geostationary Earth Orbit; HEO – Highly Elliptical Orbit; LEO – Low Earth Orbit; MEO – Medium height Earth Orbit

Space Engineering 2 © Dr. X Wu, Objectives and Requirements of a Space Mission

Space Engineering 2 © Dr. X Wu, 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

Space Engineering 2 © Dr. X Wu, Requirements of a Spacecraft 1.The payload must be pointed in the correct direction 2.The payload must be operable 3.The data from the payload must be communicated to the ground 4.The desired orbit for the mission must be maintained 5.The payload must be held together, and on to the platform on which it is mounted 6.The payload must operate and be reliable over some specified period 7.All energy resource must be provided to enable the above functions to be performed

Space Engineering 2 © Dr. X Wu, Spacecraft Subsystems Space Segment PayloadBus Structure Mechanisms Attitude and orbit control ThermalPropulsion PowerTelemetry and command Data handling

Space Engineering 2 © Dr. X Wu, 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

Space Engineering 2 © Dr. X Wu, 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 Requirements Development Detailed Design Engineering Development & Production Field (IOC)

Space Engineering 2 © Dr. X Wu, Serial (waterfall) Development 1.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

Space Engineering 2 © Dr. X Wu, Spiral Development From: And Barry Boehm, A Spiral Model of Software Development and Enhancement, IEEE Computer, 1988 Software Development Centric Example Good features 1.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 features 1.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 tests 2. Integrate components/units into subsystems 3. Perform subsystem tests 4. Integrate subsystems into spacecraft 5. Perform spacecraft level test 6. Integrate spacecraft into system 7. Perform system test when practical