Coverage Over the Satellite Graveyard

STK Free , STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this training contacting AGI Support at support@agi.com or 1-800-924-7244.

Capabilities covered

This lesson covers the following STK Capabilities:

  • STK Pro
  • Coverage

Problem statement

You need to assess a future satellite’s coverage of the satellite graveyard. The satellite graveyard is a location in the Pacific ocean around a position known as Point Nemo. At 2688 km away from any coastline, this makes it a good location for disposing of inactive satellites. For the mission, your satellite will fly over the globe with an on-board sensor. You want to know how well it will cover the region. Additionally, the satellite will be collecting ground imagery, so ideally the surface of the Earth will be illuminated.

Solution

You will use STK to model the assets in the mission (the satellite, payload, and the ground marker). After modeling the assets, you will use STK's Coverage capability to measure the coverage of this region and analyze the results.

What you will learn

Upon completion of this tutorial, you will be able to:

  • Model a Repeating Ground Trace Satellite.
  • Model a sensor on the satellite.
  • Create a place object for Point Nemo.
  • Analyze the region with the Coverage Tool.
  • Asses reports and graphs.

Figure 1: Mission Overview

Creating a New Scenario

Create a new scenario with a run time of 1 day.

  1. Launch STK ().
  2. Click the Create a Scenario () in the Welcome to STK dialog box.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name: Coverage_Tool_Point_Nemo
    Start: Default
    Stop: + 1 day
  4. Click OK to create the scenario.
  5. When the scenario loads, click Save (). A folder with the same name as your scenario is created for you.
  6. Verify the scenario name and location in the Save As dialog box.
  7. Click Save.

Save () often!

Inserting a Satellite Object

Insert a satellite object into the scenario. This satellite will have a repeating ground trace orbit. This will enable your satellite to orbit over the region of interest.

  1. Select Satellite () in the Insert STK Objects tool.
  2. Select the Orbit Wizard () method.
  3. Click Insert....
  4. Select the following in the Orbit Wizard window:
    5. Option Value
    Type Repeating Ground Trace
    Satellite Name: EarthObsSat
  5. Click OK.

Inserting a Sensor Object

Insert a Sensor () on EarthObsSat (). Use the default sensor model, which will be a conical sensor with a 45 deg half angle.

  1. Select Sensor () object in the Insert STK Objects tool.
  2. Select the Insert Default () method.
  3. Click Insert....
  4. Select EarthObsSat () in the Select Object dialog box.
  5. Click OK.

Inserting a Place Object

Insert a Place () object into the scenario. The position of this object will be Point Nemo in the Pacific Ocean. This region is used as a satellite graveyard due to the fact that the closest coastline is ~2,688 km away.

  1. Select Place () in the Insert STK Objects tool.
  2. Select the Define Properties () method.
  3. Click Insert....
  4. Ensure the Basic - Position page is selected.
  5. Set the following:
    6. Option Value
    Latitude -48.87 deg
    Longitude -123.39 deg
  6. Click OK.
  7. Right-click on Place1 () in the Object Browser.
  8. Select Rename in the shortcut menu.
  9. Rename Place1 () "Point_Nemo."

Figure 2: Satellite with payload and place marker modeled in scenario.

Intro to the Coverage Tool

Now, that you have your assets modeled in the scenario, you will use the Coverage Tool wizard to analyze a region around Point Nemo. The Coverage Tool method is unique to inserting a Coverage Definition object into a scenario. Using the Coverage Tool method enables you to do the following:

  • Create a Coverage Definition object with your specifications of regions, assets, grid points, and graphic settings.

  • Create a Figure of Merit object with your specification of type and accompanying type specifications.

Inserting the Coverage Definition object

  1. Select Coverage Definition () in the Insert STK Objects tool.
  2. Select the Coverage Tool () method.
  3. Click Insert....
  4. Type "Satellite_Graveyard" in the Name: field when the Coverage Tool opens.

Configuring the coverage definition

  1. Select Point_Nemo () in the Custom Definition Area in the Regions frame.
  2. Move () Point_Nemo () from the Custome Definition Area list to the Regions list.
  3. Set both the Semi-Major and Semi-Minor Axis to 2688 km.
  4. Set the Grid Point Granularity Lat/Lon to 2 deg.
  5. Expand () EarthObsSat () in the Assets section.
  6. Double-click Sensor1 () activate it as your coverage asset.

    7. Assets can only be selected by double-clicking on them. The term (Active) will appear next to an asset when it has been successfully selected.

  7. Confirm that Type: is Simple Coverage in the FOM Definition frame.
  8. Click OK.

Computing Coverage

The ultimate goal of coverage is to analyze accesses to an area using assigned assets and applying necessary limitations upon those accesses. You will compute coverage with the Compute Accesses tool.

  1. Select Satellite_Graveyard () in the Object Browser.
  2. Extend the CoverageDefinition menu.
  3. Select Compute Accesses. There is a progress bar in the lower right corner of STK.

Analyze the results

You can use a Figure Of Merit () object to choose a method to measure the quality of coverage.

Generating a Percent Satisfied report

  1. Right-click FigureOfMerit1 () in the Object Browser when computing accesses is complete.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select Percent Satisfied () report in the Installed Styles list when the Report & Graph Manager opens.
  4. Click Generate....
  5. Note the % Satisfied value at the bottom of the report.
  6. Minimize the report when finished.

Generating the Grid Stats Over Time graph

  1. Select Grid Stats Over Time graph () in the Installed Styles list.
  2. Click Generate....
  3. Note the Max spikes. These are when Sensor1 () is directly overhead of the region.
  4. Minimize the graph when finished.
  5. Close the Report & Graph Manager.

Viewing the Figure of Merit object

You examined your results analytically. You can enable the visualization in the Figure of Merit object.

  1. Right-click FigureOfMerit1 () in the Object Browser
  2. Select Properties ().
  3. Select the 2D Graphics page when the Properties Browser opens.
  4. Select Show Animation Graphics check box.
  5. Open the Show: shortcut menu in the Accumulation frame.
  6. Select Up to the current time.
  7. Click OK.

Visualizing the Figure of Merit object

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Point_Nem () in the Object Browser.
  3. Select Zoom To.
  4. Zoom out with the scroll wheel until you can see the satellite graveyard grid points.
  5. Click Start () in the Animation toolbar to animate your scenario. Sensor1 () will add color to the region along its path when the sensor passes over the grid points.
  6. Reset () the scenario when you are finished.

Figure 3: Visualized Coverage

Accounting for lighting conditions

You need day light to study the satellite graveyard with your satellite. You will enable a lighting constraint and apply it to your coverage definition so that the illumination is accounted for in the analysis.

  1. Right-click Point_Nemo () in the Object Browser.
  2. Select Properties ().
  3. Select the Constraints - Sun page when the Properties Browser opens.
  4. Select the Lighting: check box.
  5. Open the Lighting: shortcut menu.
  6. Select Penumbra or Direct Sun.
  7. Click OK.

Applying the lighting constraint

Set Point_Nemo () as the grid constraint. It contains the constraint you want to apply to the coverage grid.

  1. Right-click on Satellite_Graveyard () in the Object Browser.
  2. Select Properties ().
  3. Select the Basic - Grid page when the Properties Browser opens.
  4. Click Grid Constraint Options... in the Grid Definition frame.
  5. Set the Reference Constraint Class: shortcut menu in the Grid POint Access Options frame when the Grid Constraint Options dialog box opens.
  6. Select Place. For all object classes, the Basic properties of the object are applied to the grid points, excluding positional information.
  7. Select Use Object Instance check box.
  8. Select Point_Nemo in the objects list.
  9. Click OK to close the Grid Constraints Options dialog box.
  10. Click OK to accept the changes and close Properties Browser.

Determining Coverage Loss

Now that you have added in a constraint, you will reexamine the report and graphs.

  1. Maximize the Percent Satisfied report.
  2. Refresh () the report.
  3. Note the updated % Satisfied value at the bottom of the report (e.g. 78%).
  4. Minimize the report when finished.
  5. Maximize the Grid Stats Over Time graph.
  6. Refresh () the graph.
  7. Note the changes in the access times.

Figure 4: Updated Percent Satisfied Report.

The results of the tutorial may vary depending on the user settings, scenario interval, and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Summary

In this lesson you placed a satellite in a repeat ground trace orbit, then modeled a sensor on it. Then, you created a place object and defined it's position with coordinates of Point Nemo. Once the assets were modeled, you used the Coverage tool to model a coverage around the point and a Simple Coverage Figure of Merit. After examining the results, you incorporated a lighting constraint and refreshed the reports and graphs to see the changes.

On your own

On your own, explore other ways to maximize your coverage. You examined a single day, what if the scenario was longer? What if the satellite had a different orbit? Explore other ways to modify your assets or your coverage to understand the mission.