Satellite Systems Software Col. John Keesee MIT Dept. of Aero/Astro 19 October 2003 Outline ? Definitions ? Software design process ? Design rules ? Software costing Space System Software Spacecraft computer systems and their software provide unprecedented capability on orbit, but drive system cost and complexity Computer System Definitions ? Embedded System – Built-in processor providing real time control ? Real-Time processing – Handling or processing data at the time events occur ? Hard Real-Time – Precise timing required to avoid severe consequences Computer System Definitions ? Soft Real-Time – Tasks must be completed in a timely manner, but missing a time boundary has minor consequences ? Operating System Software – Manages the computer’s resources (e.g. I/O, memory) ? Application Software – Mission-specific software related to the user instead of the support of the computer Types Of Software Application Software: Operating System Software: ? Higher level functions that are ?Low level functions that provided to meet mission bridge application software requirements. to processing hardware. – Communications - Executive or run-time control – Attitude and Orbit - Kernel functions Determination and Control - Input/Output (I/O) device handlers – Navigation - Built in Test (BIT) – Autonomy - Math Utilities – Fault Detection – Mission Management – Payload Management ? Continues to increase as ?Usually will not increase requirements “creep” and after CDR. problems are encountered. Computer Resource Estimation ? Define processing tasks – Application software PDR - Operating system functions ? Estimate software size and throughput ? Establish a cost for spacecraft software ? Evaluate development and test requirements ? Create funding profile for development and test computers and equipment. ? Identify life-cycle support costs – On-orbit operations and support CDR - Upgrades, enhancements, modifications, sequence verification ? Combine resource/asset estimations to include all costs Computer Resource Estimation Functional Partitioning ? Between Space and Ground – Timing -Bandwidth – Autonomy -Human Interaction ? Between Hardware and Software – Performance -Complexity – Well-Defined Requirements -No Changes ? Between Bus and Payload – Duration -Quantity – Performance ? Alone Organizational Lines – Large Organizations -Small Team – Complexity -Accountability Computer Systems Development Process ? Define requirements – Perform functional partitioning ? Allocate top-level computer requirements – Candidate Architechtures – Functional flow analysis ? Define computer system requirements – Define tasks – Establish size and throughput estimates ? Define development and support environment ? Document and iterate Software Engineering Tasks ?Analysis ? Requirements ?Design ? Coding ? Testing and integration ?Installation and delivery ?Documentation ?Maintenance ?Quality Assurance ?Training Software Development Environment ? Target processor engineering unit(s) for software CSC integration and test. ? Work stations for all developers with centralized host for configuration management and compilation. ? Cross compiler to target processor resident on host. ? Test support equipment and associated support software. ? Realistic I/O, associated device drivers and functional simulations, resident on host. Software Test ? Usually begins with the lowest Computer Project Configuration Item and works up – Test scenarios built on the same pattern ? Increasing confidence in system performance ? Testing is a very complex activity – Often requires up to one half the development cost and a significant portion of the support cost Software Integration ? Ensures all modules/classes work together ? Ensures the program works with other software packages ? Three types of integration – Big Bang (COTS) – Bottom-up (Drivers) – Top-down (Functional stubs) Software Maintenance ? Critical to maintain a highly effective team for the life of the space system ? Software updates on orbit possible and likely ? Ground-based, high fidelity simulator is important for critical space systems Life-cycle Support ? Launch and Early Orbit Support – Is the spacecraft where it is supposed to be and operating as expected? ? Trouble-Shooting: Parameter or Code Changes – If a problem occurs: Why? How? When? – Review data to understand – Develop work-around – Change parameters or upload new software ? Data Retrieval, Reduction, and Analysis – Housekeeping and status information – Payload and/or science data Memory and Throughput Margin Requirements ? At SRR, size hardware to be four times the estimated requirement ? Reserve a full 100% margin (i.e., twice the delivered size and speed) at launch Software Reliability Measures ? Watchdog timers ensure system restarts automatically if the processor stalls ? Operating system manages “Stuck” memory bits and Single Event Upsets ? High reliability systems maintain backup software images Sixteen Critical Software Practices ? Project Integrity 1. Adopt continuous program risk assessment 2. Estimate cost and schedule empirically 3. Use metrics to manage 4. Track earned value 5. Track defects against quality targets 6. Treat people as the most important resource Sixteen Critical Software Practices ? Construction Integrity 7. Adopt life cycle configuration management 8. Manage and trace requirements 9. Use system-based software design 10. Ensure data and database interoperability 11. Define and control interfaces 12. Design twice, code once 13. Assess reuse risks and costs Sixteen Critical Software Practices ? Product Stability and Integrity 14. Inspect requirements and design 15. Manage testing as a continuous process 16. Compile and smoke test frequently Spacecraft Software Costing SMAD Chapter 20 Engineering Estimates ? Costs - - (FY00$) ? Costs - - estimate hours – Flight Software -Flight Software (QA) $435 * lines of code 6 hours / line of code – Ground Software -Ground Software $220 * lines of code 3 hours / line of code ? Fee not included ? Dollar estimates calculated from hours ? Language dependent (but ? Amount of testing and should be tailored based on Quality Assurance support personnel experience and reuse) influence costs – Ada as baseline FIRESAT Example: Overview ? Three axis stabilized vehicle ? MIL-STD-1750A processor / Ada ? Spacecraft Bus Functions: – ACS: 5200 SLOCs - - Earth sensor, Sun Sensor, rate gyros, reaction- control thrusters, kinematic integration, ephemeris propagation, error determination. – C & DH: 725 SLOCs - - Command and telemetry processing – Other: 500 SLOCs - - Power management, thermal control ? Fire Detection using remote IR sensor ? Payload Functions: – Fire Detection: 666 SLOCs - - sensor processing – Fire Reporting: 205 SLOCs - - data reduction and transmission FIRESAT Example: Cost Elements SOFTWARE DEVELOPMENT SUPPORT EQUIPMENT ? Nearly 8,000 SLOC for ?Estimate 4 Engineering Units on-board software (MIL-STD-1750) ? Estimate at least 24,000 ? MIL-STD-1750 compiler SLOC in avionics and run-time kernel simulation software ? Main Frame Computer ? Estimate at least 8,000 and workstations (10) SLOC in data collection ? Compiler(s), GUI builder and reduction software and CM Tools ? Ground station interface ? I/O cards, card cage, and and simulation software drives FIRESAT Example: Costing ? On-Board Software Development $3.48M – 8,000 SLOC * $435/SLOC ? Support Software Development $7.04M – 32,000 SLOC * $220/SLOC ? Software Support Equipment $1.00M – Main Frame ($200K) / Workstations and S/W (10 * $20K) – Engineering Units (4 * $100K) – Cross Compiler ($150K) / Run-Time Kernel ($40K) ? Test Support Equipment $0.35M – Compilers (2 * $50K) / GUI ($50K) / CM ($50K) – I/O Cage (2 * $15K) / Cards (6 * $15K) / Drivers (3 * $10K) ? TOTAL COSTS: $11, 870,000.00 Application Software Size Estimates ? SMAD Table 16-13, page 665, is based on 16-bit words, a 1750A class instruction set architecture, and a higher order language – Communications – Attitude Sensor Processing – Attitude determination and control – Autonomy – Fault Detection – Other functions (power management, thermal control) Operating System Software Sizing Estimates ? SMAD table 16-15, page 667, is based on similar systems—16-bit words and a 1750A class instruction set architecture – Executive – Run-time kernel – I/O device handlers – Built-in test and diagnostics – Math utilities COCOMO ? Developed by B. Boehm (Software Engineering Economics, Prentice Hall, 1981) ? Computes the amount of effort and time to complete a software project – Breaks project into WBS elements – Requires estimate of the new lines of code required to complete each requirement Basic COCOMO Formula E=a b * K * exp(b b ) (person-months of effort) D=c b * E * exp(d b ) (duration in months) Where K is the total number of lines of code. Software Project Type a b b b c b d b Small project, experienced team, flexible requirements (“organic”) 2.4 1.05 2.5 0.38 Hard real-time requirements and strict interoperability (“embedded”) 3.6 1.2 2.5 0.32 A mixture of the two other types of projects (“intermediate”) 3.0 1.12 2.5 0.35 http://www.jsc.nasa.gov/bu2 http://sunset.usc.edu/research/COCOMOII/index.html Conclusion References ? Wertz, James R. and Wiley J. Larson, Space Mission Analysis and Design, Microcosm Press, Torrance CA, 1999 ? Leach, Ronald J., Introduction to Software Engineering, CRC Press, New York NY, 2000