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The Spacecraft Simulator

The Spacecraft Simulator. David S. Davis, GSSC. Simulation of GLAST attitude and orbit dynamics Tailored version of “42: The Mostly Harmless Simulation” ANSI C for portability Environment Models IGRF 2000 Geomagnetic Field Model Jacchia-Roberts Atmosphere Density Model

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The Spacecraft Simulator

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  1. The Spacecraft Simulator David S. Davis, GSSC

  2. Simulation of GLAST attitude and orbit dynamics Tailored version of “42: The Mostly Harmless Simulation” ANSI C for portability Environment Models IGRF 2000 Geomagnetic Field Model Jacchia-Roberts Atmosphere Density Model EGM-96 Earth Gravity Model (Non-spherical geopotential) Attitude and Orbit evolve under influence of forces and torques Aerodynamic, Gravity Gradient, Solar Radiation Pressure Non-spherical geoid, third-body (e.g. Sun, Moon) Gravity Attitude Control Torques Visualization using OpenGL graphical libraries Written by Eric Stoneking, beginning August 6, 2001 The Mostly Harmless Simulator

  3. Attitude Control in “GLAST 42” approximately models GLAST Guidance Navigation & Control (GNC) flight software Performs pointing, Sun avoidance, Earth avoidance, solar array pointing Doesn’t always meet all performance requirements Sun and Earth avoidance during transients Comes close, but it is NOT FLIGHT SOFTWARE GNC Flight Software may be incorporated at later date The flight software will be expected to meet performance requirements GNC Software Disclaimer

  4. GLAST 42 Visualization

  5. Visualizing Fields of View, Keep-Out Zones

  6. Master Input File defines sim parameters, environment Sim duration, file output interval Date, time Order of geomagnetic and geopotential models Toggle disturbances ON/OFF Spacecraft Input File defines spacecraft parameters, initial conditions Mass, inertias Initial orbit, attitude Command Input File models Sky Survey, Pointed Observation commands Geometry Files define spacecraft as a solid model Used for disturbance force/torque calculation and visualization Spacecraft Commands

  7. Desired quantities written to files at specified intervals Position, attitude Pointing direction (RA, Dec) Longitude, latitude of subsatellite point Sun incidence on LAT radiators Attitude control variables Attitude errors Reaction wheel commands, momenta Magnetic torquer dipole commands Easily customizable Simulator Outputs

  8. Simulator Outputs

  9. Spacecraft Simulator Uses at the GSSC Exploring Observing Strategies Pointed mode vs Scanning mode Scanning strategies Mode transitions Does Not Handle SAA passage Auto re-pointing

  10. Conclusions • Simulator provides a flexible method of determining S/C pointing parameters • Can provide tables of position and pointing data • Can take a long time to run

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