Improving Analysis with the Navigation Analysis Plugin

One of my favorite STK 11 plugins is the Navigation Analysis plugin. If you do any analysis on GPS satellites in STK 11, this plugin will enable you to quickly add satellite outages and add navigation uncertainties.

Whenever I teach a L1 & L2: STK Comprehensive class, the first thing we do is update our databases. If you work with GPS satellites, this is very important. We open a new scenario and load a Satellite object using the Load GPS Constellation method. This loads the satellites from the GPS Almanac. You can specify the location of your external GPS almanac, or use the almanac that’s downloaded from the AGI server. The GPS almanac is a set of data that every GPS satellite transmits, and it includes information about the state (health) of the entire GPS satellite constellation, and coarse data on every satellite's orbit.

Once the satellites are loaded into the scenario and you have the Navigation Analysis plugin installed, using your mouse, you can right click on the GPS Constellation object, select Constellation Plugins, and then select Add GPS Satellite Outages which opens the plugin. If you don’t have an Internet connection, you can use your own Satellite Outage File (SOF). If you have Internet, the plugin does the work for you. If there are any outages, the plugin will change the affected satellites properties and turn the Satellite off for analysis during its reported outage interval.

In this example, there are numerous outages during the analysis period. In one of the satellite’s properties, you can see that the interval is enabled and the satellite is excluded from analysis during its reported outage time.

The interval file was created and inserted by the Add GPS Satellite Outages tool.

More information can be found at the AGI Satellite Outage Calendar.

GPS is often used during Search and Rescue (SAR) operations. STK Coverage will allow you to accurately predict your navigation accuracy over a specified analytical period. After setting up and computing coverage in a defined area, you can measure the accuracy of your navigation solution. Using position accuracy, the STK Figure of Merit uncertainties model defaults the asset range uncertainty to a constant value of one (1) meter. The default receiver range uncertainty is zero (0) meter.

Right click on the Figure of Merit object, select Figure of Merit plugins, and then select Add Navigation Uncertainties which brings up the Add Navigation Uncertainties tool. You can use your own Prediction Support File or download one from the AGI server. You can find more information at the AGI GPS Satellite Performance Website.

Once you have updated the uncertainties using the plugin, all of your satellites will be updated for you as you can see in this example.

Just think how long it would take to manually input the asset and receiver range uncertainty values.

The Navigation Analysis plugin not only adds realism to your analysis, but it saves you a lot of time!


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