The orbital path of the satellite named Polar.
A selection of Cosmos satellites.

SOS for Windows - Version 25.1 (710 downloads)

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This download has been digitally signed, but Windows will 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.

Satellite Orbit Simulator V25 (SOS) Features/Capabilities

  1. Three-body solutions that include bulging Earth, lunar gravity and sun gravity.
  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 launch 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 tracks.
  11. Earth rotation, lunar orbit, and Sun location accurately synchronized with date and time. Use it to observe solar eclipses in past or future.
  12. Multiple ways to enter initial conditions: position and velocity vectors, orbital elements, Lagrange points and Two Line Elements (TLEs).
  13. Finds and accepts TLEs based on NORAD Catalog IDs and satellite name.
  14. Simulation with play, pause, single step, forward wind, and rewind buttons.
  15. View from a point in space, the satellite, or your location on Earth.
  16. Lists Solar Eclipses for a particular location.
  17. Save and share your projects in editable JSON files.
  18. Comes with a free book on space mission design using SOS and lots of example project files.
  19. Free for educational use.

Release Notes


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


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


  • Tutorial changed.


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


  • 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.


  • 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.


  • 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.


  • 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.