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 12.2 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.

  1. Launch STK ().
  2. Click the Create a Scenario () in the Welcome to STK dialog.
  3. Enter the following in the STK: New Scenario Wizard:
    4. 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
  4. Click OK when you finish.
  5. Click Save () when the scenario loads. STK creates a folder with the same name as your scenario for you.
  6. Verify the scenario name and location in the Save As window.
  7. Click Save .

Save often during this lesson!

Disabling Terrain Server

You will not use Terrain in this analysis, so you can turn off the Terrain Server.

  1. Right-click on Attitude_Cov () in the Object Browser.
  2. Select Properties ().
  3. Select the Basic - Terrain page.
  4. Clear the Use terrain server for analysis check box.
  5. Click OK.

Inserting a Ship object

The Ship object models the properties and behavior of a ship.

  1. Select Ship () in the Insert STK Objects window.
  2. Select the Insert Default () method.
  3. Click Insert...
  4. Right-click on Ship1 () in the Object Browser.
  5. Select Rename in the shortcut menu.
  6. Rename Ship1 () to Test_Ship.
  7. 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.

  1. Select the Basic - Route page.
  2. Set Reference: to WGS84 in the Altitude Reference frame. You turned off Terrain Server. WGS84 is the central body's reference ellipsoid.
  3. Click Insert Point two times.
  4. Set waypoints one and two:
    5. Latitude Longitude
    19.00 deg 125.00 deg
    12.00 deg 140.00 deg
  5. Click Apply .

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.

  1. Browse to the 3D Graphics - Attitude Sphere page.
  2. Enable Show in the Attitude Sphere.
  3. Set the Value: to 2.0 in the Scale section.
  4. Click Frame: Select .
  5. Select Body () in the Axis For: Test_Ship list.
  6. Click OK.
  7. Click Apply.

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.

  1. Browse to the 3D Graphics - Vector page.
  2. Enable Sun Vector - Show in the Vectors tab.
  3. Locate the Common Options - Component Size section.
  4. Set Scale Relative to Model - Scale: to 2.0.
  5. Click OK.
  6. Bring the 3D Graphics window to the front.
  7. 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.

  1. Insert a Sensor () object using the Insert Default () method.
  2. Select Test_Ship () in the Select Object dialog box.
  3. Click OK.
  4. Rename Sensor1 () to Sensor_FOV.
  5. Open Sensor_FOV's () properties ().
  6. Select the Basic - Definition page.
  7. Set the Cone Half Angle to 90 deg in the Simple Conic frame.
  8. Select the 3D Graphics - Attributes page.
  9. 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.
  10. Click Apply.

Setting the Sun Constraint

Sun Constraints enable you to impose constraints based on the position of the Sun and Moon.

  1. Select the Constraints - Sun page.
  2. Enable Solar Exclusion Angle: in the Boresight frame.
  3. Set the Solar Exclusion Angle: value to 10 deg. 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).
  4. Click OK.

Propagating the GPS satellites

Use the Standard Object Database tool to query the online Spacecraft database from which to create GPS satellites in STK.

  1. Insert a Satellite () object using the From Standard Object Database () method.
  2. Enter GPS in the Name or ID: field when the Standard Object Database tool opens.
  3. Click Search.
  4. Click Operational Status twice in the Results: list so that the arrow points down.
  5. Select all the Operational satellites.
  6. Select Create Constellation from Selected in the Insert Options frame.
  7. Enter All_Sats in the Name: field.
  8. Click Insert.
  9. Click Close to exit the Standard Object Database tool when all the satellites are propagated.

Attitude Coverage

STK's Attitude Coverage capability combines features of the Attitude and Coverage capabilities to enable you to analyze coverage in various directions over time, using several attitude-dependent figures of merit. Using Attitude Coverage, determine the most advantageous direction to point the sensor. You are only concerned when a satellite is five (5) degrees above the horizon to 90 degrees above the ship.

  1. Insert an Attitude Coverage () object using the Insert Default () method.

    2. 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.

  2. Select Test_Ship () in the Select Object dialog box.
  3. Click OK.
  4. Rename AttitudeCoverage1 () to Sat_Cov.
  5. Enable Sat_Cov () in the object Browser.

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.

  1. Open Sat_Cov's () properties ().
  2. Select the Basic - Grid page.
  3. Set the following Grid Area of Interest options:
    4. Option Value
    Type Latitude Bounds
    Min. Latitude 5 deg
    Max. Latitude 90 deg
  4. Set the Lat/Lon value to 10 deg in the Point Granularity frame.
  5. Click Apply.

3D graphics attributes

  1. Select the 3D Graphics - Attributes page.
  2. Change Color: to yellow in the Static Graphics frame.
  3. Sent Point Size: to 4. These settings will make the points easier to view in the 3D Graphics window.
  4. Click Apply .

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.

  1. Bring the 3D Graphics window to the front.
  2. 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

Grid Constraints

Sensor_FOV has a 10 degree Solar Exclusion Angle constraint which needs to be applied to the grid.

  1. Return to Sat_Cov's () properties ().
  2. Select the Basic - Grid page.
  3. Click Grid Constraint Options... in the Grid Definition frame.
  4. Enable Use Object Instance for Constraints in the Grid Point Access Options frame.
  5. Ensure Object Class: shows Sensor.
  6. Select Test_Ship/Sensor_FOV
  7. Click OK.
  8. Click Apply .

Coverage assets 

You can use Assets properties to specify the STK objects used to provide coverage.

  1. Select the Basic - Assets page.
  2. Select All_Sats () in the Assets list.
  3. Click Assign .
  4. Click OK.

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.

  1. Select Sat_Cov () in the Object Browser.
  2. Open the AttitudeCoverage menu.
  3. Click Compute Accesses. STK may take a few minutes to compute accesses on the attitude sphere.

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 Attitude Figure Of Merit (FOM) object to the Attitude Coverage object that will define the required quality of coverage.

  1. Insert an Attitude Figure Of Merit () object using the Insert Default () method.
  2. Select Sat_Cov () in the Select Object dialog box.
  3. Click OK.
  4. 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.

  1. Open NAsset's () properties ().
  2. Select the Basic - Definition page.
  3. Set the following:
    4. Option Value
    Type: N Asset Coverage
    Compute: Minimum
  4. Click Apply.

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.

  1. Right-click on NAsset () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Grid Stats report in the Installed Styles folder when the Report & Graph Manager opens.
  4. Click Generate....
  5. Scroll to the bottom of the report and note the Maximum value (e.g. 9).
  6. Close the report and the Report & Graph Manager.

Graphic 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.

  1. Return to NAsset's () properties ().
  2. Select the 3D Graphics - Animation page.
  3. Disable the Show Animation Graphics check box.
  4. Click Apply .
  5. Select the 3D Graphics - Static page.
  6. Change % Translucency to 30.
  7. Enable the Show Contours option in the Display Metric frame.

Adding levels

  1. Set the following in the Level Adding frame:
    2. Option Value
    Start 0 (Minimum value from the Grid Stats report)
    Stop 9 (Maximum value from the Grid Stats report)
    Step 1
  2. Click Add Levels.
  3. Set the following in the Level Attributes frame:
    4. Option Value
    Color Method Color Ramp
    Start Color Red
    End Color Blue
  4. Click Apply .
  5. Click Legend...
  6. Click OKto close NAsset's () properties ().
  7. Expand the Static Legend for NAsset dialog box so you can see all the values.

Viewing the Contours

  1. Bring the 3D Graphics window to the front.
  2. Use the mouse to zoom out until you can see the entire Attitude Sphere.

    3. 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.

  3. Close Static Legend for NAsset when finished.

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!

  1. Close any reports and tools that are still open once you are finished.
  2. 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.