Satellites plugin

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==Introduction==
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{{obsolete|12 November 2011 (but the problem dates from before that)}}
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The Satellites plugin simulates satellites in Earth orbit.  Satellite orbits are not very precisely predicted using the existing orbital models for the planets, as there are other factor involved - irregularities in the Earth's gravitational field, lunar interactions, atmospheric drag and so on.   
 
The Satellites plugin simulates satellites in Earth orbit.  Satellite orbits are not very precisely predicted using the existing orbital models for the planets, as there are other factor involved - irregularities in the Earth's gravitational field, lunar interactions, atmospheric drag and so on.   
  

Revision as of 20:26, 12 November 2011

Some or all of the information on this page is no longer accurate.

It may be relevant to an older version of Stellarium, or it may not be relevant at all. This page itself should be updated, archived or deleted.

This warning has been here since 12 November 2011 (but the problem dates from before that).


The Satellites plugin simulates satellites in Earth orbit. Satellite orbits are not very precisely predicted using the existing orbital models for the planets, as there are other factor involved - irregularities in the Earth's gravitational field, lunar interactions, atmospheric drag and so on.

This plugin implements the SGP4 and SDP4 models, and takes as it's input data NORAD TLEs (two line elements). TLEs for hundreds of satellites are available online and are regularly updated.

Contents

Usage

Enabling the Satellites plugin

This plugin comes bundled with Stellarium version 0.10.3, although it is not enabled by default. To enable the plugin, open the configuration dialog and go to the plugins tab. Click Satellites from the list of available plugins and check the load at startup checkbox. You will need to re-start Stellarium for changes to take effect.

Using the Satellites plugin

To see the position of artificial satellites, you must have the observer location set to Earth. You must also turn on Satellite indicators on the main tool bar as shown in the image below:

sat_howto_02.jpg

Searching for satellites

It should now be possible to search for artificial satellites using the regular search dialog (F3). Note that at any given time, most Satellites will be below the horizon.

sat_howto_03.jpg

Diaplaying satellite data

When you have selected a Satellite, information about it will be shown just as for any other object which is selected. This includes:

  • Normal positional data (RA/Dec, Alt/Azi and so on)
  • Range in kilometers. This is the line-of-sight distance between the observer and the selected satellite
  • Range Rate in kilometers per second. This is the closing/parting speed of the satellite. It is useful when calculating doppler shift necessary for communications (and is also just nice to know)
  • Altitude of the satellite above the ground in kilometers
  • Comms data. Some satellites broadcast on frequencies which can be received by the general public or used by amateur radio operators. Where such data is known about a satellite Stellarium will show it.


sat_howto_04.jpg

Configuration

When the satellites plugin is loaded, the configuration button in the plugins tab of the configuration dialog will be enabled. Clicking this button (or pressing Control+Shift+Z) will open the configuration dialog for the satellites plugin.

Settings tab

In the settings tab you can control how often the Satellites plugin downloads updates for the TLE elements of known satellites. The default is every 72 hours. If an update is due when Stellarium is started, it will commence 30 seconds or so after the plugin is loaded.

sat_howto_05.jpg

Satellites tab

The Satellites tab shows data on known satellites and lets you choose which ones are visible. Note that for each satellite which is visible, Stellarium must do extra work to calculate and show the position of the satellite. If Stellarium is running very slowly with the Satellites plugin enabled, try reducing the number of satellites which are visible.

You can select and go to a satellite by double clicking it in the list.

At time of writing, this dialog is only doe display information about satellites and changing their visibility. In future it will be possible to edit descriptions, comms data and so on, but this is not yet implements.

sat_howto_06.jpg

Sources tab

The Sources tab lets you see (and modify) where Stellarium is getting its TLE data from. The default is a list of sources from celestrak.com.

sat_howto_07.jpg

Adding new Satellites

At time of writing, there is no simple way to add and remove satellites using the GUI. However, you can modify the satellites.json file manually using a text editor.

Before editing your satellites.json, make a backup copy. Leaving out the smallest detail (such as a comma or forgetting to close a curly bracket) will prevent Stellarium from starting.

The path to the directory in which satellites.json can be found is something like:

  • C:\Users\Username\AppData\Roaming\Stellarium\modules\Satellites (Vista)
  • C:\Documents and Settings\Username\Application Data\Stellarium\modules\Satellites (Windows XP)

To add a new satellite, open a new line after line 5 and paste the following, note commas and brackets, they are important:

		"satellite name": 
		{
			"description": "description goes here",
			"comms": [
			   {
				"description": "downlink 1",
				"frequency": 437.49,
				"modulation": "AFSK 1200 bps"
			   },
			   {
				"description": "downlink 2",
				"frequency": 145.825
			   }
                        ],
			"groups": ["group1", "group2"],
			"tle1": "1 12345U 90005D   09080.85236265  .00000014  00000-0  20602-4 0  5632",
			"tle2": "2 12345 98.2700  53.2702 0011918  71.1776 289.0705 14.31818920   653",
			"visible": true
		},
  • satellite name - required parameter, double quoted with a colon following. Use the name as it appears in source you are updating from if you want the TLE to be automatically updated. Use the description field for a more readable name if you like.

The remaining parameters should be includes in curly brackets, the closing curly bracket must be followed by a comma to separate it from the next satellite in the list.:

  • description - optional parameter, double quoted. Appears when you click on the satellite
  • comms- optional parameter, square bracketed list of curly bracketed communications information.
  • groups - optional parameter, comma separated list of double quoted group names contained in square brackets. Used for grouping satellites in the drop down box on the config (see above)
  • tle1 - required parameter, line 1 of the TLE, must be contained in double quotes and begin with "1 "
  • tle2 - required parameter, line 2 of the TLE, must be contained in double quotes and begin with "2 "
  • visible - required parameter, set to true if you want to see it, this can be toggled from the config once loaded.

You can edit the tags for a satellite, modify the description and comms data, and even add new satellites.


Satellites.json Creator

A user (LCoronelP) has written a satellites.json creator in PHP using the TLE sources in your config.ini, you can use it here, and the sourcecode is here.

Note: This generator only works if your sources are OK.

Additional Sources for TLE data

TODO

  • Provide download links for alternative satellites.json files which include specialist lists of satellites.
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