Support &ndash Freefall on iOS

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Panoramic View

The panoramic view displays the positions in the sky of satellites and other celestial objects from the perspective of the selected location at the specified time. The display can be customized from the Settings. Drag anywhere in the view to change the orientation or pinch to zoom. Tap-hold on a satellite to select it.

Location

To change the location, tap-hold on the current city displayed in the lower-right corner. Freefall includes a database of over 75,000 world cities that can be searched by name or by distance from the current location. To choose a location close to you, tap the "Find Near Current Location" button and select an item from the list that appears. If the current location cannot be determined, or if there are no nearby cities in the database, find a location by its name. To find a location by name, tap the search field and start typing. The search is very fast and the results display dynamically with every keystroke. Search results may be obscured by the keyboard on iPhone or iPod Touch devices (particularly in landscape orientation).

Timeline

At the bottom left corner, the play-pause button toggles the simulation running state. Opening menus or other interactions with the timeline pause the simulation because the intense computations of a running simulation interfere with application responsiveness. Dragging the timeline left or right will change the simulation time; a tap-hold on the timeline will set the simulation time to the nearest hour.

Satellites

Access satellites from this menu. A satellite will be highlighted white if it is visible from the current location at the current time, and disabled (gray) if it is not. Tap a visisble satellite to center it in the display. Tapping a disabled (not visible) satellite will do nothing.

Planets

This menu includes the moon and other planets in our solar system. Like satellites, the planet (or moon) will be highlighted white if it is visible from the current location at the current time, and disabled (gray) if it is not. Tap a visible item to center it in the display. Tapping a disabled (not visible) item will do nothing.

Constellations

The 88 official constellations are included in this menu. The constellation will be highlighted white if it is visible from the current location at the current time, and disabled (gray) if not. Tap a visible constellation to center it in the display. The determination of constellation visibility is somewhat different than that for a planet or deep-sky object; constellations near the horizon may be considered 'visible' but not appear in the display.

Deep-Sky (Messier) Objects

Like satellites, planets, and constellations, Messier objects that are visible are highlighted in white; otherwise they are disabled (gray).

Settings

Use the Settings menu to customize Freefall.

About Freefall

Satellites

Freefall uses industry-standard SGP4 and SDP4 algorithms to predict satellite motion. Accurate predictions require current orbital parameters that can be downloaded from the Internet using your Space-Track account.

Planets & Moon

Planet positions are calculated using VSOP87. The position of the moon is approximated using a truncated series from Chapront ELP-2000/82. Venus image processing by R. Nunes.

Stars, Constellations, and Messier Objects

The positions of the stars, constellations, and Messier objects are computed using techniques described in Jean Meeus' excellent book on the subject, "Astronomical Algorithms." Freefall uses the 9110 stars described in the Bright Star Catalog, heasarc_bsc5p. Many of the Messier object atlas images obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Panoramic Background

The 360° x 180° panoramic image used for a background was taken in Littleton, Colorado.

Information about Space-Track

To keep your satellite models current and the predictions accurate, you need a free Space-Track account. Fortunately, getting one is fairly easy:

Step 1: Register

Register for a new account at:

www.space-track.org/perl/new_account.pl

Space-Track administrators will create a user account for you and send an initial password to the email address you provide. Please note that this process may take a few days; it does not appear to be fully automated. If you haven't received an email from Space-Track within a few days of your registration, check your junk mail or contact Space-Track administration, admin@space-track.org.

Step 2: Change Your Password

Before using your new Space-Track account in Freefall, login to www.space-track.org/perl/login.pl from Safari or another web browser. The system may require that you change your password at your initial login.

Step 3: Enter your Credentials

Once you have successfully logged in to Space-Track from a web browser and have verified that your username and password work, enter them into the fields above.

More Information

Freefall uses industry-standard orbit propagation algorithms, SGP4 and SDP4, to predict satellite motion. These algorithms require occasional updates to the satellite orbital information (commonly known as 'TLEs' or 'Elements') for accurate predictions. Distribution of this orbital information is restricted by US federal law. Space-Track, a system managed by US Air Force Space Command, is the exclusive provider of this information; redistribution is prohibited. Freefall can use your user account to download this information directly from Space-Track, but we cannot redistribute it from our own servers. We are not in any way associated with Space-Track.

Accuracy of the Predictions

Although we have taken much care to ensure that the predictions are accurate, there is a lot that can go wrong (and probably will). If you notice any errors or have any suggestions, please help us improve Freefall by sending an email to freefall@advancedanalytic.com.