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The orbital path of the satellite named Polar.
A selection of Cosmos satellites.
Satellites orbiting the Moon using Orbital Elements

SOS for Windows (5000 downloads )

Please read…

Please ensure your Windows OS is up-to-date before installing. We support Windows 10 and 11, but Windows 11 will have the better experience. We use the latest Microsoft .NET10 software. So if your OS is not up-to-date you maybe prompted to install this when first running the application.

This download has been digitally signed with an OV certificate, but Windows may warn against installing due to it being an “unrecognized app” or “rarely downloaded app”. This is because we do not have an EV signing certificate. We are unable to get one as we are not a registered organization. The warnings are different depending on which Windows version you have. Often you need to click “More info” and “Run anyway” to install, but you may be presented with something else. But there is always a way to accept the download and install it.

New – Tutorials on YouTube

Please visit and subscribe to our YouTube channel for tutorials on SOS and orbital mechanics.

Donating

This is a completely free application. If you would like to help with the running costs of this site and the code signing certificate, which amount to several hundred dollars a year, we would appreciate the support. This will go to direct costs, not recompensing our time or effort. In the very unlikely event we receive monies way beyond this, they will go to an appropriate charity. Please visit this page

Satellite Orbit Simulator V29.0 (SOS) Features/Capabilities

  1. Solves the Newtonian equation of motion for a near-Earth spacecraft using Earth gravity, lunar gravity, solar gravity, atmospheric drag, atmospheric lift, thrust, and solar pressure as inputs. Numerical integrators that you may choose from are Euler, Velocity Verlet, and Runge-Kutta 4th Order.
  2. Simulate multiple satellites concurrently.
  3. Multiple propulsion methods: impulse ∆v, long-duration low-thrust, solar pressure.
  4. User friendly with lots of new tools for making space mission design fast and easy.
  5. User-defined Earth surface observer location.
  6. User-defined Earth atmospheric drag and lift using the NRLMSISE-00 atmosphere density model.
  7. High resolution 3D imagery with mouse-controlled zoom, rotate, shift, etc. 
  8. Three Earth images to choose from.
  9. Accurate star map providing realistic space background.  Labels are optional.
  10. Ground and Sky tracks, which are relative to the rotation of the Earth.
  11. Also, satellite tracks relative to the motion of the Moon.
  12. Earth rotation, lunar orbit, and Sun location accurately synchronized with date and time. Use it to observe solar eclipses in past or future.
  13. Multiple ways to enter initial conditions: position and velocity vectors, orbital elements, Lagrange points and Two Line Elements (TLEs).
  14. Finds and accepts TLEs based on NORAD Catalog IDs and satellite name.
  15. Simulation with play, pause, single step, forward wind, and rewind buttons.
  16. View from a point in space, the satellite, or your location on Earth.
  17. Lists Solar Eclipses for a particular location.
  18. Script based Mission Planner
  19. Create Videos and Photos.
  20. Export Simulation Data and Events.
  21. Save and share your projects in editable JSON files.
  22. MCP server for connecting to an AI
  23. Comes with a free tutorial on space mission design using SOS and lots of example project files.
  24. Free for educational use.
  25. Plus many other features.

Release Notes

V29.0.3

  • Fixed bug in getting old TLE info that no longer exists.
  • Updated NuGet files.
  • Added ability to save project notes.

V29.0.2

  • Fixed window placement issue.
  • Updated SOS MCP Guide.
  • Added missing file: Script functions.md (used by the MCP)

V29.0.1

  • Added OpenAI Codex setup button.

V29.0.0

MCP (Model Context Protocol) AI Integration

  • Added MCP server integration allowing AI assistants (e.g. Claude Desktop) to control the simulator
  • Added MCP Client Setup dialog for configuring AI assistant connections
  • Added comprehensive MCP tools: satellite CRUD, TLE import, scene/camera control, screenshots, data export, physics settings, project management,
    mission planner scripting, delta-V creation, thrust, labels, events, and more
  • Added MCP replay log and diagnostic replay app for debugging AI interactions
  • Added MCP notifications for user actions (project load, simulation start/stop, satellites)

Mission Planner / Scripting

  • Added CallScriptIf and CallScriptSwitch for conditional script branching with input variable support
  • Added FindApogeePerigee, FindNode, FindAtTime script functions
  • Added SetIntegrator function and integrator params to SetSimulationWindow
  • Added TargetApsisRadius script functions
  • Added SetSatBurnoutOrbit and Burnout to Orbit UI tab
  • Added satellite creation methods: orbital elements, burnout, parking orbit, Lagrange
  • Added Parse Script button for syntax-only validation
  • Added progress bar and cancel button during script simulation calculations
  • Added bool type coercion to Irony DSL

Orbital Mechanics & Physics

  • Enhanced Earth bulge model with J3 and J4 zonal harmonics
  • Improved drag/lift calculation: handle low velocity and LST bug
  • Added precise delta-V refinement using simulation feedback
  • Fixed Moon orbit creation bug; clamped perigee; added Moon orbit tests
  • Improved orbital period edge case handling and robustness for non-elliptical orbits
  • Added EventFinder improvements: culmination jitter fix, missing burns, pre-epoch guard
  • Added satellite pitch parameter support

UI & Layout

  • Migrated shell layout from frame navigation to Syncfusion DockingManager (docking/floating panels)
  • Added “Play Backwards” simulation control
  • Added Manage Labels dialog
  • Added themed borders, dark mode fixes for auto-hide tab strips and floating windows
  • Changed button text from uppercase to normal case globally
  • Added proprietary licence, third-party notices, and licence UI tab

Window Management

  • Added single-instance enforcement: activates existing window instead of launching a second copy
  • Remember window size, position, and state across restarts

V28.4.0

  • Added integrators: Velocity Verlet and Runge-Kutta 4th Order.
  • Updated NuGet files.
  • Updated tutorial.
  • Now using .NET 10 framework.
  • Minor bug fixes.

V28.3.1

  • The time of a satellite’s epoch was sometimes shown incorrectly in an event.
  • Updated NuGet files.

V28.3.0

  • You can now export simulation data to Excel, CSV or JSON.
  • It is now possible to run the simulation in reverse.

V28.2.5

  • Fixed introduced bug in ground steps calculation function.

V28.2.4

  • Fixed issues when running SOS on Windows 10.

V28.2.3

  • Updated NuGet files.
  • Updated a couple to formulas shown in the UI.

V28.2.2

  • Improved the dialog for getting TLEs. More performant and more functionality.
  • Added the ability to see a satellites path across the sky.
  • Updated NuGet files.
  • Updated tutorial.

V28.2.1

  • Bug fix for UTC/Location functionality.
  • Bug fix for updating a satellite in a multi-satellite project.
  • Improved Location functionality by including location name, UTC offset and Time Zone name.
  • Updated tutorial.

V28.2.0

  • Can now change moon orbits using orbital elements and the Delta-V dialog.
  • You can now display satellite orbit lines relative to the motion of the Moon.
  • Automatically selects whether to use Earth or Moon’s orbital elements throughout the application.
  • Added a Default Project option, which is not affected by user preferences.
  • Added ability to select a satellite by clicking on it.
  • Added new projects.
  • Updated tutorial.
  • Updated NuGet files.

V28.1.1

  • Minor bug fixes.
  • Added undo/redo to the menus and added icons to menu items.
  • Updated About page.
  • Updated NuGet files.
  • Updated tutorial.

V28.1.0

  • Option to show satellite name labels
  • Minor bug fixes.
  • Improvements on simulation calculation and redraw speed.
  • Added menu options to open website and YouTube channel.
  • Updated NuGet files.

V28.0.0

  • Camera control rewritten.
  • Can now create videos.
  • Can now take photos.
  • Can now export events.
  • Added common operations to the menu and created hotkeys.
  • Added new satellite models.
  • Added the ability to call Mission Planner scripts while the simulator is running.
  • Added new functions and abilities to Mission Planner.
  • Tutorial has been updated and new topics added.
  • Updated NuGet files.

V27.0.2

  • Bug Fix. Reverted some NuGet files due to a problem with the script editor.

V27.0.1

  • Bug fix. Better behaviour when trying to save to read-only files or directories.
  • Updated comments and visual aspects to some project files.
  • Updated the tutorial.
  • Updated NuGet files.

V27.0.0

  • Added Mission Planner, a built-in script engine for designing missions using Orbital Elements.
  • Bug fixes.
  • The tutorial has been updated and new topics added.

V26.0.1

  • Bug fixes for the displaying and calculating DeltaV.
  • Spelling typo corrected.
  • The tutorial has been updated.

V26.0.0

  • Added a Moon Camera view positioned at L1.
  • Large performance enhancements on calculating and simulating orbits.
  • Now using .NET 8 framework.
  • Can now have a satellite epoch within the time simulation window (not just at the beginning). The simulator will work out the track before the epoch.
  • Added the ability to calculate satellite orbits around the Moon using Orbital Elements.
  • Within the simulator, you can now quickly go to any point in time within the simulation.
  • Added the ability for a project to always use the current time. Useful for projects that follow satellites using TLEs. Find out where the ISS is by just opening the project!
  • The tutorial has been updated and new topics added.

V25.2.0

  • The display settings are now stored in the project file and are now found in the project pane.
  • You can now pick a color for each satellite orbit line.
  • On application startup, you are now presented with the new project defaults. These can be changed and saved.
  • The most recent previously loaded projects can now be quickly reloaded via a new button in the project pane.
  • There are now ‘Expander Bars’ on the side panels to allow you to hide each side panel. This allows more screen space for the simulation.
  • The tutorial has been updated.

V25.1.0

  • Can now visually hide the ‘step’ spheres.
  • You can now change the orbit line thickness.

V25.0.3

  • Fixed bug: Vector to orbital elements routine could fail.
  • Fixed bug: Set Initial Parameters dialog not initializing to correct tab when using vectors.

V25.0.2

  • Tutorial changed.

V25.0.1

  • Fixed bug – The Date/Time combo box was showing ‘Off’ rather than ‘UTC’.

V25.0.0

  • Can now optionally calculate the Sun’s pull on a satellite.
  • Can now place a satellite’s starting coordinates at an Earth-Moon Lagrange point.
  • You can now also have a line showing a satellite’s path and/or moon’s path.
  • With very long simulations, the application no longer has to save each DeltaT data point. But is able to recreate the dropped data points if required. This preserves accuracy and memory.
  • DeltaT has now been taken away from the UI and defaults to one second. The project can have a DeltaT of another value, but it now will need to be altered in the project file.
  • Earth view can now track stars.
  • New examples added to the tutorial.

V24.2.0

  • With projects having satellite orbits based on TLEs, if you change the epoch (project start time) and then recalculate orbit, a dialog will ask you whether you want to fetch new TLEs and so create new initial coordinates.
  • Added the ability to show Ecliptic and Equatorial lines.
  • Reduced the file size of the Earth image with clouds for faster loading.
  • You can now click on the location marker and get a popup telling you, its location.
  • Most distances now shown in km rather than metres. Now also use the thousands separator too. This is to make the values easier to read.
  • Fixed bug when calculating Azimuth/Elevation on track popups.
  • Updated the tutorial and added a couple of projects.

V24.1.0

  • Added the ability to show the major planets.
  • You can now find solar eclipses for a specified location. This can be found in the “Set New Location” dialog.
  • Now shows solar eclipse events in the “More Info” dialog.
  • Fixed UI bug when project has no satellites.
  • Made some speed improvements on redraw.
  • Added to the tutorial and added a new project.

V24.0.0

  • Supports multiple satellites in one project.
  • Introduced the NRLMSISE-00 air density model for more accurate drag and lift calculations.
  • Earth view can now show azimuth labels.
  • Now saves camera position in the project file.
  • Added orbital period to “More Info” dialog.
  • Improved satellite behaviour on crashing or landing.
  • Updated tutorial and added more projects.