alex-developer/isat

Satellite Orbit Tracker: implement most-current SGP models and algorithms in JavaScript, then use to visualize hundreds of satellites with any browser

SOT: Satellite Orbit Tracker

Goal

We are developing a replacement for the functionality of JTrack-3D which uses the SGP4 algorithms to calculate satellite positions and renders them in 3D using the Cesium engine -- completely in the browser, implemented as JavaScript.

(Dis)Claimer

This is my first attempt at JavaScript. I also haven't used MATLAB until now.

As such, my JavaScript code is not following good practices for structure, modularity, loading, inhertiance, etc, etc. I'm starting with bare JavaScript before using jQuery, RequireJS, AMD, etc. I'm learning, and the Cesium code is really a good exemplar.

Overview

I've translated the SGP algorithms from MATLAB which we believe to be the best current propagator implementation; see Miura's PhD thesis. It's a direct translation and has some very un-JavaScript structure, including globals used by the original FORTRAN and MATLAB implementations. This needs to be restructured. I've written tests to capture MATLAB calculations and translated them to validate the JavaScript implementation.

We use NORAD Two Line Element (TLE) data which describes the last known position, velocity, and orbital parameters for each satellite. These are pulled from Dr. T.S. Kelso's site Celestrak.com which is canonical for public data and updated frequently. Currently the TLE files are stored with the code for development, but we plan to have the browser download them directly and cache them locally using HTML5 local storage.

AGI's Cesium is an excellent virtual globe and map engine, built on WebGL, and open sourced on GitHub. It would not be possible for us to provide sophisticated visualizations without this software.

We believe client-side JavaScript is the best way to deliver this content to users without requiring plugings (e.g., Eyes On The Solar System's requirement for the Unity game engine, or World Wind's Java download). While not all browsers support WebGL now, most desktops browsers do and mobile is improving. Running client-side means we do not need a farm of servers to stream satellite locations to clients: the calculations are done in the browsers themselves.

The code here is divided into two areas: SGP4 satellite calculations and Cesium-based visualizaiton.

Trying it out

It would be nice if you could clone this code, then open the viz/index.html file in a browser. Unfortunately, images and globe backgrounds won't render due to cross-domain issues "SECURITY_ERR: DOM Exception 18" on Chrome. Firefox seems to render everything fine. Safari renders the images but for me is stalled loading the tiles from Bing (beachball of death).

Instead, put the unpacked files into a place your web server can see them, then hit the index.html. On my Mac, I put it under ~/Sites/

Browser support

I'm developing on OS X.

I primarily use Chrome (22.0.1229.94) to visualize it.

Firefox 16.0 and 17.0 have worked fine for me.

Safari 6.0.1 doesn't have WebGL support unless you enable it: Preference, Advanced, Show Develop menu in menu bar; Develop menu, Enable WebGL.

Android CyanogenMod 9 on HP TouchPad:

• The stock browser partially renders some statellites and globe, but then hangs.
• Firefox runs and displays the calculations but shows me a blank screen.
• Dolphin: TBD

Android CyanogenMod 7 on Nook Color:

• Stock browser: TBD
• Firefox: TBD
• Dolphin: TBD

Android CyanogenMod (SuperSonic) 7.2.0 on HTC Evo 3G (2+ years old):

• Stock Browser: Renders UI controls which work, but no globe or positions displayed
• Firefox: Renders UI controls which work, but no globe or positions displayed
• Dolphin: Renders UI controls which work, but no globe or positions displayed