ISS Transit Prediction


OVERVIEW
This application generates International Space Station (ISS) Transit Predictions for the Sun, Moon and Planets.

The user specifies a location, which includes latitude, longitude and elevation.  The application downloads the latest ISS orbital information. The application generates a transit prediction map which contains prediction paths for each transit within a specified alert radius.

Specify and save multiple locations
Save multiple prediction maps for later viewing
User specified Two Line Elements
Add transit prediction to Calendar
View maps with Google Earth

USER INTERFACE
The main screen provides 4 buttons:
The options menu provides the following:
LOCATIONS
Add a named observing location by clicking the "Add Location" button accessible from the locations screen.

The location coordinates can be entered in any of three methods:
Use the locations page accessible from the options menu to edit and delete saved locations.

TWO LINE ELEMENT (TLE) SETS
The application requires satellite orbital Two Line Elements to accurately generate a prediction. By default, the application downloads elements from the CelesTrak website via the Supplemental TLE web page. These TLEs are generated from ephemeris state vectors provided by the NASA Open Data portal. These elements are generated about twice a week, and normally span about 12 days.
An option is available to generate elements using NASA ephemeris data, similar to those provided by the CelesTrak supplemental TLEs web page (Android version 7 or better).
An option is available to download elements via the CelesTrak current NORAD TLEs web page. These TLEs are derived from radar and optical observations. These TLEs are generated every few hours, but do not span into the future.
Each element contains an "epoch" time. The closer the epoch time is to the prediction time, the more accurate the prediction. The TLE source can be changed in the Two Line Elements download setting. The TLE button gives an indication if new orbital data is available.

Pressing the TLE button downloads the latest elements from the default TLE Source.  If transits are found during the generation of a prediction, the TLEs used for the prediction are displayed within the Transit Prediction text file.

The prediction text file includes the number of days that the TLE set spans (TLE Span).  For more accurate predictions, the specified prediction span setting should be no longer than a day or so past the TLE Span.

The prediction text file includes the longest difference between TLE epoch and prediction epoch (TLE Age) in days.  The closer the TLE Age is to zero days, the more accurate the prediction.

GENERATING PREDICTIONS
Once a location has been entered and TLE have been downloaded, press the "Generate Prediction" button to begin prediction generation.  The progress bar gives an indication of how long it will take to complete the process.  Depending on your CPU speed, it can take a few minutes to generate the predictions.  Pressing the cancel button will cancel the prediction.

VIEWING PREDICTIONS
Once the prediction generation is complete, the prediction map or text file can be viewed.  Pressing the View Prediction button brings up the previously generated prediction map.  The text button within the map view displays the prediction text.  The Map/Sat button switches between Map mode and Satellite mode.

Within the map view press the Google Earth button to view the map in Google Earth.  Press the save button to save the prediction for later viewing.
Within the transit information window, press the add to calendar button to create a calendar event.
Use the predictions page accessible from the options menu to view, share and delete previously saved prediction maps.

SETTINGS
The following settings can be specified via the settings page:

DEM DATA
The DEM Data is downloaded as needed from the Elevation Data Source setting page.  The USGS has organized world elevations into "tiles" of 40 degrees of longitude by 50 degrees of latitude.  Only the DEM Data near the selected location is needed.  Typically this is only one tile, but could be as many as 4 tiles, if the selected location is near (within 5 degrees of) a DEM tile boundary.  For example, a location in Los Angeles, CA (118W, 34N) would need the DEM data in tile W140N40.  However, a location in San Francisco, CA (122W, 38N) would need two tiles (W140N90 and W140N40).  The DEM data is provided in a compressed format.  The application downloads and uncompress the needed DEM data.


View ISS Transits Predictions on the web