ISS Transit Prediction Free Help

ISS Transit Prediction Free

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 orbital information. The application generates a transit prediction map which contains prediction paths for each transit within a specified alert radius.

Pro Only: No Ads.
Pro Only: Specify and save multiple locations.
Pro Only: Save multiple prediction maps for later viewing.
Pro Only: User specified Two Line Elements.
Pro Only: Add transit prediction to Calendar.
Pro Only: View maps with Google Earth.

Pro Only: Available in-app purchase: Unlock Additional Satellites: Compute transits for any satellite, including the Tiangong Space Station and Hubble Space Telescope.

USER INTERFACE

The main screen provides 5 buttons:

Location - Press this button to add or select the prediction generation location. Long press to view the options menu.
Pro Only: Satellite - Press this button to change the transit satellite (In-app purchase required).
Two Line Elements (TLE) - Press this button to download orbital elements. Long press to view the elements text.
Generate Prediction - Press this button to start the prediction generation.
View Prediction - Press this button to view the prediction map or text file. Long press to view the predictions menu.

The options menu provides the following:

Pro Only: Locations - Press to add, select, edit or delete saved locations.
Pro Only: Predictions - Press to view, share or delete saved prediction maps.
Settings - Press to set user preferences.
DEM Files - Press to list or delete the downloaded DEM Data.
Help - Press to display this help page.
About - Press to display application version, credits and links.

LOCATIONS

Add a named observing location by clicking the "Location" button accessible from the main screen.

The location coordinates can be entered in any of these methods:

Manually - Enter latitude, longitude and elevation in the text boxes. Positive values represent North and East, negative values South and West. Elevation can be entered in meters or feet above sea level depending on the current prediction units setting. Once the coordinates are entered, the map pans to the location.
Search - Press the search button to search for a location.
Map Input - Use the map to zoom and pan to a location. Pressing the Set button sets the location name, coordinates and elevation in the text boxes. The elevation of the current coordinates is retrieved using the specified elevation data source setting. Switch between map and satellite modes by toggling the Map/Sat button.
GPS - By pressing the GPS button, the application uses GPS to obtain location coordinates and elevation.

Pro Only: 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 ISS 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 processor 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. For each transit, the blue line represents the centerline of the transit. If you are on the blue line, you would see the satellite transit through the center of the sun, moon or planet. The red lines represent the limits of the transit. If you are between the two red lines you would see a transit. If you are outside the red lines you would see no transit.

The text button within the map view displays the prediction text. The Map/Sat button switches between Map mode and Satellite mode.

Pro Only: 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.
Pro Only: Within the transit information window, press the add to calendar button to create a calendar event.
Pro Only: 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:

Transit Bodies - Brings up a page which specifies the transit bodies for which predictions are generated from the following:
- Moon (Transit in shadow)
- Moon (Transit in sunlight)
- Mercury
- Venus
- Mars
- Jupiter
- Saturn
- Sun
Transit Body Update Times - Can be specified via additional settings on the Transit Bodies page. A setting is provided for the Sun, Moon and Planets. These settings are used to update the position in the sky of the transit body at the interval specified. Shorter update times give more accurate predictions. Larger update times give faster predictions.
Minimum Transit Elevation - Select the minimum elevation angle for which transits predictions are generated - Horizon (0) to the local Zenith (90). A value of 0 degrees generates predictions for the entire sky. The default value is 10 degrees above the horizon.
Prediction Units - Specifies if distances should be measured in metric (meters, kilometers) or imperial (feet, miles) units.
Alert Radius - Specifies the maximum distance from the selected location to look for transits (up to 241.5 kilometers or 150 miles). The default value is 160.9 kilometers or 100 miles.
Prediction Span - Specifies the time span to look for transits (starting now, up to 30 days). The default value is 11 days.
Timezone - Specifies timezone offset from Coordinated Universal Time (UTC), negative numbers are west, positive numbers are east. Check the box to have the timezone automatically selected.
TLE Download - Specifies automatic or manual TLE download. In automatic mode, TLE sources are picked in the following order: CelesTrak Supplemental, CelesTrak Current NORAD, Application generated from NASA ephemeris. In manual mode, the user specifies the TLE source and must manually press the TLE button to initiate the download.
Pro Only: An option is also available for a user-provided TLE file. This setting is provided to allow use of separately downloaded elements (e.g., from SpaceTrack.org). Press the Open TLE File button to browse to any file containing TLEs. Elements can be provided in both TLE and OMM XML formats. More information about TLE and OMM XML formats can be found here. Only elements for the currently selected satellite can be specified. An example TLE file for the ISS follows:

1 25544U 98067A 13293.55472222 .00014076 00000-0 25605-3 0 8456
2 25544 051.6517 207.1515 0002900 046.2774 302.5149 15.49789271854148
TLE Update Check Interval - Specifies how often to check the TLE source for new orbital data.
Elevation Data Source - Specifies how the application obtains elevation data:
- Download U.S. Geological Survey (USGS) Digital Elevation Model (DEM) data - Predictions are more accurate.
- - Specify whether DEM data is automatically downloaded or not.
- Use the elevation of the selected location for all elevations - Predictions are less accurate.
Default GPS - Specify if GPS should be on automatically when entering a location.
Notifications - Posted when prediction runs in the background.
Language - Change the language. Changing this setting requires an application restart.

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