Attitude Coverage
STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this training by contacting AGI Support at support@agi.com or 1-800-924-7244.
This lesson requires STK 12.9 or newer to complete it in its entirety.
The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.
Problem statement
A ship in the Western Pacific Ocean is equipped with a sensor that needs to maintain access to as many GPS satellites as possible. The sensor needs to keep a boresight of 10 degrees or more from the Sun during its 24-hour analysis period. If you wanted to determine what direction to point the sensor, you would need to analyze coverage in various directions over time, using several attitude-dependent figures of merit.
Solution
You can determine the best direction for the sensor to point by finding the direction that tracks the highest minimum amount of satellites. That direction ensures you will track the most satellites during the 24-hour analysis period. You still need to constrain the sensor to avoid the sun by at least ten (10) degrees. An Attitude Sphere centered on the ship will be used for situational awareness. With the Systems Tool Kit (STK), you can model this entire scenario with all these mission requirements and find the best direction for the sensor.
What you will learn
Upon completion of this tutorial, you will have a basic understanding of the following:
- The Attitude Sphere
- Solar Exclusion Angles
- Attitude Coverage objects
Video guidance
Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).
Creating a new scenario
First, you must create a new STK Scenario and then build from there.
- Launch STK ().
- Click the Create a Scenario () in the Welcome to STK dialog.
- Enter the following in the STK: New Scenario Wizard:
- Click when you finish.
- Click Save () when the scenario loads. STK creates a folder with the same name as your scenario for you.
- Verify the scenario name and location in the Save As window.
- Click .
Option | Value |
---|---|
Name: | Attitude_Cov |
Location | Default |
Start | 15 Mar 2022 07:00:00.000 UTCG |
Stop | 16 Mar 2022 07:00:00.000 UTCG |
Save often during this lesson!
Disabling Terrain Server
You will not use Terrain in this analysis, so you can turn off the Terrain Server.
- Right-click on Attitude_Cov () in the Object Browser.
- Select Properties ().
- Select the Basic - Terrain page.
- Clear the Use terrain server for analysis check box.
- Click .
Inserting a Ship object
The Ship object models the properties and behavior of a ship.
- Select Ship () in the Insert STK Objects window.
- Select the Insert Default () method.
- Click
- Right-click on Ship1 () in the Object Browser.
- Select Rename in the shortcut menu.
- Rename Ship1 () to Test_Ship.
- Open Test_Ship's () Properties ().
Creating Test_Ship's route
You can add a route to your ship so it moves as it interacts with the other objects in the scenario.
- Select the Basic - Route page.
- Set Reference: to WGS84 in the Altitude Reference frame. You turned off Terrain Server. WGS84 is the central body's reference ellipsoid.
- Click two times.
- Set waypoints one and two:
- Click .
Latitude | Longitude |
---|---|
19.00 deg | 125.00 deg |
12.00 deg | 140.00 deg |
Adding an Attitude Sphere
The Attitude Sphere is a visual aid that you can add to the 3D Graphics and 3D Attitude Graphics windows. When combined with vector displays, the Attitude Sphere makes a powerful tool for displaying the object's attitude and for tracking attitude changes over time. You need to orient the attitude sphere so that zero (0) degrees longitude matches the ship's direction of travel. This can help later on when orienting the sensor when tracking the GPS satellites.
- Browse to the 3D Graphics - Attitude Sphere page.
- Enable Show in the Attitude Sphere.
- Set the Value: to 2.0 in the Scale section.
- Click Frame: .
- Select Body () in the Axis For: Test_Ship list.
- Click .
- Click .
Adding a Sun vector
A Sun vector is useful in visualizing that a sensor attached to the ship avoids the sun by at least ten (10) degrees.
- Browse to the 3D Graphics - Vector page.
- Enable Sun Vector - Show in the Vectors tab.
- Locate the Common Options - Component Size section.
- Set Scale Relative to Model - Scale: to 2.0.
- Click .
- Bring the 3D Graphics window to the front.
- Zoom To Test_Ship ().
Attitude Sphere
Attaching a Sensor to the Ship
The Sensor object models the field of view and other properties of a sensing device attached to another STK object.
- Insert a Sensor () object using the Insert Default () method.
- Select Test_Ship () in the Select Object dialog box.
- Click .
- Rename Sensor1 () to Sensor_FOV.
- Open Sensor_FOV's () properties ().
- Select the Basic - Definition page.
- Set the Cone Half Angle to 90 deg in the Simple Conic frame.
- Select the 3D Graphics - Attributes page.
- Set % Translucency: to 100 in the Projection frame. This is done to avoid the sensor cone in the 3D Graphics window, which would interfere with the display of the attitude sphere.
- Click .
Setting the Sun Constraint
Sun Constraints enable you to impose constraints based on the position of the Sun and Moon.
- Select the Constraints - Active page.
- Click Add new constraints () in the Active Constraints toolbar.
- Select Boresight - Solar Exclusion Angle in the Constraint Name list when the Select Constraints to Add dialog box opens.
- Click .
- Click to close the Select Constraints to Add dialog box.
- Use the default Solar Exclusion Angle: of 10 deg.
- Click .
This ensures that Sensor_FOV will ignore access to another object if it is within ten (10) degrees of the Sun (exclusion angle is ten (10) degrees).
Propagating the GPS satellites
Use the Standard Object Database tool to query the online Spacecraft database from which to create GPS satellites in STK.
- Insert a Satellite () object using the From Standard Object Database () method.
- Enter GPS in the Name or ID: field when the Standard Object Database tool opens.
- Click .
- Click Operational Status twice in the Results: list so that the arrow points down.
- Select all the Operational satellites.
- Select Create Constellation from Selected in the Insert Options frame.
- Enter All_Sats in the Name: field.
- Click .
- Click to exit the Standard Object Database tool when all the satellites are propagated.
Using the Attitude Coverage capability
STK's
- Insert an Attitude Coverage () object using the Insert Default () method.
- Select Test_Ship () in the Select Object dialog box.
- Click .
- Rename AttitudeCoverage1 () to Sat_Cov.
- Enable Sat_Cov () in the object Browser.
If you do not see Attitude Coverage and Attitude Figure Of Merit options in the Insert STK Objects tool, click Edit Preferences to add them.
Setting point definition properties
In contrast to point definition in the STK Coverage capability, here you are defining the properties of the object pointing, which depends on the directions represented by points on the coverage grid. That object must be a sensor, transmitter, receiver, or radar whose parent object is the one for which Attitude Coverage is being defined.
The basic properties of that object (such as a sensor's field-of-view), including its position at each time step in the coverage interval and any constraints imposed on it, determines the access to the selected assets. These properties are also taken into account in Figure of Merit computations.
- Open Sat_Cov's () properties ().
- Select the Basic - Grid page.
- Set the following Grid Area of Interest options:
- Set the Lat/Lon value to 10 deg in the Point Granularity frame.
- Click .
Option | Value |
---|---|
Type | Latitude Bounds |
Min. Latitude | 5 deg |
Max. Latitude | 90 deg |
Changing the 3D Graphics attributes
- Select the 3D Graphics - Attributes page.
- Change Color: to yellow in the Static Graphics frame.
- Sent Point Size: to 4. These settings will make the points easier to view in the 3D Graphics window.
- Click .
If you were doing this operationally, you would probably require a grid with more points. For the purposes of this lesson, the grid contains less points due to the amount of time it would take to compute more points.
Viewing the Attitude Coverage grid
View the Attitude Coverage grid in the 3D Graphics window.
- Bring the 3D Graphics window to the front.
- Mouse around in the 3D Graphics window to view the Attitude Coverage grid.
You can see the grid spans from 5 degrees to 90 degrees latitude every 10 degrees.
Grid Points
Adding Grid Constraints
Sensor_FOV has a 10 degree Solar Exclusion Angle constraint which needs to be applied to the grid.
- Return to Sat_Cov's () properties ().
- Select the Basic - Grid page.
- Click in the Grid Definition frame.
- Enable Use Object Instance for Constraints in the Grid Point Access Options frame.
- Ensure Object Class: shows Sensor.
- Select Test_Ship/Sensor_FOV
- Click .
- Click .
Specifying coverage assets
You can use Assets properties to specify the STK objects used to provide coverage.
- Select the Basic - Assets page.
- Select All_Sats () in the Assets list.
- Click .
- Click .
Using the Compute Accesses tool
Your can use coverage to analyze accesses to an area with assigned assets and apply necessary limitations upon those accesses. The Compute Accesses tool enables you to compute accesses between the grid points and the assigned assets.
- Select Sat_Cov () in the Object Browser.
- Open the AttitudeCoverage menu.
- Click Compute Accesses. STK may take a few minutes to compute accesses on the attitude sphere.
Adding an Attitude Figure Of Merit object
Determine the best direction in which to point the sensor in order to maximize access from the sensor to the satellites in the constellation. Add an
- Insert an Attitude Figure Of Merit () object using the Insert Default () method.
- Select Sat_Cov () in the Select Object dialog box.
- Click .
- Rename AttitudeFigureOfMerit1 () to NAsset.
Measuring Number of Assets
N Asset Coverage measures the number of assets available simultaneously during coverage, where N is between zero and the total number of assets defined in the coverage definition. You want to examine the lowest number of satellites that you can track by pointing the sensor at various locations. By selecting the location with the highest minimum, you can maximize tracking of the satellites.
- Open NAsset's () properties ().
- Select the Basic - Definition page.
- Set the following:
- Click .
Option | Value |
---|---|
Type: | N Asset Coverage |
Compute: | Minimum |
Generating a Grid Stats report
Generate a Grid Stats report to determine the highest minimum value. Use this number to create a graphical display of the results in the Attitude Sphere that you can visualize in the 3D Graphics window.
- Right-click on NAsset () in the Object Browser.
- Select Report & Graph Manager... () in the shortcut menu.
- Select the Grid Stats report in the Installed Styles folder when the Report & Graph Manager opens.
- Click .
- Scroll to the bottom of the report and note the Maximum value (e.g. 9).
- Close the report and the Report & Graph Manager.
Displaying coverage contours
You can display coverage contours on the attitude sphere for Attitude Coverage just as you can on the map and globe for traditional coverage.
- Return to NAsset's () properties ().
- Select the 3D Graphics - Animation page.
- Disable the Show Animation Graphics check box.
- Click .
- Select the 3D Graphics - Static page.
- Change % Translucency to 30.
- Enable the Show Contours option in the Display Metric frame.
Adding levels
- Set the following in the Level Adding frame:
- Click .
- Set the following in the Level Attributes frame:
- Click .
- Click
- Click to close NAsset's () properties ().
- Expand the Static Legend for NAsset dialog box so you can see all the values.
Option | Value |
---|---|
Start | 0 (Minimum value from the Grid Stats report) |
Stop | 9 (Maximum value from the Grid Stats report) |
Step | 1 |
Option | Value |
---|---|
Color Method | Color Ramp |
Start Color | Red |
End Color | Blue |
Viewing the contours
- Bring the 3D Graphics window to the front.
- Use the mouse to zoom out until you can see the entire Attitude Sphere.
- Close Static Legend for NAsset when finished.
FOM CONTOURS
The blue areas have the highest level of minimum coverage. The path in red shows a coverage level of zero (0). No GPS satellites will be visible to the sensor in the red zone. If you animate the scenario, you can see the sun vector trace a path right through most of the red swath.
You have determined where the most ideal locations would be to aim your sensor boresight under nominal circumstances in order to maximize your tracking of the satellites.
Summary
You inserted into the scenario a Ship object cruising in the Western Pacific Ocean. You enabled an attitude sphere around the ship and aligned the sphere using the ship's body axis. Then, you turned on a sun vector inside the attitude sphere.
You inserted a Sensor object into the scenario and set its field of view to mimic what the ship's pointing sensor can see. You set the boresight solar exclusion angle to ten (10) degrees. The Sensor object won't report any accesses in this area.
Using the Insert STK Objects Tool, you inserted operational GPS satellites into the scenario and grouped them into a Constellation object. Next you inserted an Attitude Coverage object and set the coverage using latitude bounds from 5 to 90 degrees latitude. You constrained the coverage to the sensor's field of view, and used the GPS satellites as your assets.
After computing coverage, you inserted an Attitude Figure of Merit object and set it to use Number of Asset Coverage and computed Minimum. This allowed you to determine the maximum minimum number of satellites your sensor would see when pointing it at various locations in the coverage grid.
Next, you used a Grid Stats report to determine your minimum and maximum values. Using static graphics, you used the minimum and maximum values to visualize colors inside the attitude sphere which allowed you to determine in which direction to point your sensor to maximize tracking of all the satellites.
Save your work
- Close any reports and tools that are still open once you are finished.
- Save () your scenario.
On your own
Throughout the tutorial, hyperlinks were provided that pointed to in depth information of various subjects. Now's a good time to go back through this tutorial and view that information.