Using Chains with 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.

Capabilities Covered

This lesson covers the following STK Capabilities:

  • STK Pro
  • Coverage

Problem Statement

You are designing a constellation of imaging satellites that will provide imagery of the Continental United States. The imaging satellites do not have on-board storage. They must send near-real-time imagery to a ground station. In order for the imaging satellites to send imagery to the ground station, they must either have a direct connection with the ground station or an indirect connection via a relay satellite.

Solution

You will use STK to design a constellation of imaging satellites, a relay satellite, and the ground station. You will then use STK's Coverage capability to determine the percentage of the Continental United States that can be observed over the course of one day using:

  • A direct connection between the imaging satellites and the ground station
  • An indirect connection from the imagining satellites to the ground station via a relay satellite

What You Will Learn

Upon completion of this lesson, you will understand:

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, create a new STK scenario.

  1. Launch STK ().
  2. Click Create a Scenario in the Welcome to STK dialog box.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name: Chains_Coverage
    Location: Default
    Start: 15 Jun 2023 16:00:00.000 UTCG
    Stop: + 24 hr
  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

Analytical and visual terrain is not required in this analysis. Turn off the Terrain Server.

  1. Right-click on Chains_Coverage () in the Object Browser.
  2. Select Properties ().
  3. Select the Basic - Terrain page.
  4. Clear Use terrain server for analysis.
  5. Click OK to accept the changes and close the Properties Browser.

Creating a Seed Satellite (Imaging Satellite)

The original satellite that is used to create the Walker constellation is referred to as the “Seed” satellite. The satellites generated using the Walker Tool are referred to as children. Use the Orbit Wizard to create the “seed” satellite from which the other satellites will be derived.

  1. Select Satellite () in the Insert STK Objects tool.
  2. Select the Orbit Wizard () method.
  3. Click Insert....
  4. Set the following in the Orbit Wizard:
    5. Option Value
    Type: Circular
    Satellite Name: Imager
  5. Click OK.

Creating a Satellite Camera

Use a Sensor () object to simulate the field of view of your camera.

  1. Insert a Sensor () object using the Insert Default () method.
  2. Select Imager () in the Select Object dialog box.
  3. Click OK.
  4. Right-click on Sensor1 () in the Object Browser.
  5. Select Rename.
  6. Rename Sensor1 () to Camera.
  7. Open Camera's () properties ().
  8. Enter 10 deg in the Simple Conic - Cone Half Angle: field.
  9. Click OK.

Creating a Walker Constellation (Imager Satellites)

The Walker Tool makes it easy to generate a Walker constellation using the Two Body, J2, J4, or SGP4 orbit propagators. Use the Walker Tool to create a Walker constellation containing all the Imager satellites.

  1. Right-click on Imager () in the Object Browser.
  2. Select Satellite in the shortcut menu.
  3. Select Walker... in the second shortcut menu.
  4. Set the following in the Walker Tool:
    5. Option Value
    Type: Delta
    Number of Sats per Plane 1
    Number of Planes: 6
  5. Select Create Constellation in the Container Options - Select Option shortcut menu.
  6. Enter Imager_Satellites in the Name field.
  7. Click Create / Modify Walker.
  8. Click Close when finished.

Understanding Walker Satellite Relationships

When a Walker constellation is created, each child has the same base name as the seed satellite plus two numbers. The first number identifies the plane in which the satellite resides and the second identifies the satellite's position in the plane. For instance, here we define a Walker constellation six (6) planes and one (1) satellite per plane. Imager11 () is the satellite in the first plane. If the seed satellite has sub-objects such as sensors, the sub-objects are also created for each of the child satellites.

The seed satellite Imager () and Imager11 () are identically configured satellites. You can delete Imager () after saving your scenario.

  1. Click Save ().
  2. Select Imager () in the Object Browser.
  3. Click Delete () in the Object Browser toolbar.
  4. Click Delete when prompted.

Creating a Constellation Object

Use the Insert STK Objects tool to load a Constellation () object. The Constellation () object models a set of related objects. For your analysis, you will group all the Imager cameras into a Constellation () object.

  1. Insert a Constellation () object using the Insert Default () method.
  2. Rename Constellation1 () to Imager_Cameras.
  3. Open Imager_Cameras' () properties ().
  4. Select the Basic - Definition page when the Properties Browser opens.
  5. Select the Sensor () check box in the Select filter: frame. This selects all the Sensor () objects in the Available Objects list.
  6. Move () the Sensor () objects from the Available Objects list to the Assigned Objects list.
  7. Click OK.

Creating a Seed Satellite (Relay Satellite)

Use the Orbit Wizard to create the “seed” satellite from which the relay satellites will be derived.

  1. Insert a Satellite () object using the Orbit Wizard () method.
  2. Set the following in the Orbit Wizard:
    3. Option Value
    Type: Circular
    Satellite Name: Relay
    Inclination: 60 deg
    Altitude: 2000 km
  3. Click OK.

Creating a Walker Constellation (Relay Satellites)

Create a Walker constellation containing all the Relay satellites.

  1. Right-click on Relay () in the Object Browser.
  2. Select Satellite in the shortcut menu.
  3. Select Walker... in the second shortcut menu.
  4. Set the following in the Walker Tool:
    5. Option Value
    Type: Delta
    Number of Sats per Plane 1
    Number of Planes: 6
  5. Select Create Constellation in the Container Options - Select Option shortcut menu.
  6. Type Relay_Satellites in the Name field.
  7. Click Create / Modify Walker.
  8. Click Close when finished.

Removing the Seed Satellite (Relay)

The seed satellite, Relay (), and Relay11 () are identically configured satellites. You can delete Relay () after saving your scenario. By saving the scenario first, Relay () is saved as an object file, Relay.sa, in the scenario folder. When Relay () is deleted from the scenario, the object file remains in the folder. The object can be loaded back into the scenario at a later time if desired.

  1. Click Save ().
  2. Select Relay () in the Object Browser.
  3. Click Delete () in the Object Browser toolbar.
  4. Click Delete when prompted.

Modeling the Ground Site

Use the default Facility () object to simulate the location of the ground site that will receive data from the satellites.

  1. Insert a Facility () object using the Insert Default () method.
  2. Rename Facility1 () to Ground_Site.

Creating a Chain Object (Direct Connection)

The Chain Object is a list of objects (either individual or grouped into constellations or satellite collection subsets) in order of access. Create a Chain () object that represents a direct connection from the Imager satellites to the ground site. The Relay satellites will not be used.

  1. Insert a Chain () object using the Insert Default () method.
  2. Rename Chain1 () to Direct_Connection.
  3. Open Direct_Connection's () properties ().
  4. Select the Basic - Definition page.
  5. Move () the following objects from the Available Objects list to the Assigned Objects list in the order shown:
    Available Object
    Ground_Site ()
    Imager_Satellites ()
    Imager_Cameras ()
  6. Click OK.

Creating a Chain Object (Indirect Connection)

Create a Chain () object that represents an indirect connection from the Imager satellites to the ground site. The Relay satellites will be used.

  1. Insert a Chain () object using the Insert Default () method.
  2. Rename Chain2 () to Indirect_Connection.
  3. Open Indirect_Connection's () properties ().
  4. Select the Basic - Definition page.
  5. Move () the following objects from the Available Objects list to the Assigned Objects list in the order shown:
    Available Object
    Ground_Site ()
    Relay_Satellites ()
    Imager_Satellites ()
    Imager_Cameras ()
  6. Click OK.

Modeling an Area Target

The Area Target () object models a region on the surface of the central body. In this case, you are focusing your analysis inside the Continental United States.

  1. Insert an Area Target () object using the Select Countries and US States () method.
  2. Select United_States_of_America in the list when the Select Countries And US States dialog box opens.
  3. Click Insert.
  4. Click Close to close the Select Countries And US States dialog box.
  5. Zoom In () to the United_States_of_America () in the 2D and 3D Graphics windows if you desire.

2D and 3D Graphics View of the Continental United States

Coverage Definition Object (Direct Connection)

The Coverage Definition () object defines a coverage area for analysis. You will use the first Coverage Definition () object to analyze coverage using Direct_Connection ().

Inserting a Coverage Definition

Insert a Coverage Definition () object into your scenario.

  1. Insert a Coverage Definition () object using the Insert Default () method.
  2. Rename CoverageDefinition1 () to US_Cov.

Defining the Grid Area of Interest

Define the coverage grid using the United_States_of_America ().

  1. Open US_Cov's () properties ().
  2. Select the Basic - Grid page.
  3. Select Custom Regions in the Grid Area of Interest - Type shortcut menu.
  4. Click Select Regions....
  5. Move () United_States_of_America () from the Area Targets list to the Selected Regions list when the Select Regions... dialog box opens.
  6. Click OK to close the Select Regions... dialog box.
  7. Click Apply to accept your changes and keep the Properties Browser open.

Setting the Grid Definition

The statistical data computed during a coverage analysis is based on a set of locations, or points, which span the specified grid area of interest. You are focusing your grid inside United_States_of_America ().

  1. Enter 1 deg in the Point Granularity - Lat/Lon field.
  2. Click Apply.

Assigning Coverage Assets

Assets properties enable you to specify the STK objects used to provide coverage. Define the Direct_Conection () as the Coverage Asset.

  1. Select the Basic - Assets page.
  2. Select Direct_Connection () in the Assets list.
  3. Click Assign.
  4. Click OK.
  5. Look at your 2D and 3D Graphics windows. Your coverage grid is displaying in both windows.

    6. Coverage Grid

Computing Access

The ultimate goal of coverage is to analyze accesses to an area using assigned assets and applying necessary limitations upon those accesses. Compute coverage for US_Cov () with the Compute Accesses tool.

  1. Select US_Cov () in the Object Browser.
  2. Select the CoverageDefinition menu item.
  3. Select Compute Accesses.

Inserting a Figure of Merit

You can evaluate the quality of coverage for an area by creating one or several Figure Of Merit () objects attached to the coverage definition of interest. Insert a Figure of Merit (FOM).

  1. Insert a Figure Of Merit () using the Insert Default method.
  2. Select US_Cov () in the Select Object dialog box.
  3. Click OK.
  4. Rename FigureOfMerit1 () to Simple_Cov.
  5. Look at the 2D and 3D Graphics windows.

    6. Direct Simple Coverage

    The default FOM is Simple Coverage which measures whether or not a point is accessible by any of the assign assets. You can see from looking at the 2D and 3D Graphics windows that you don't have 100% coverage. You want to determine the actual percentage of coverage.

Determining Direct Coverage Percent Satisfied

You are interested in Simple Coverage and the percentage of coverage over the Continental United States. The default Figure Of Merit () object automatically measures simple coverage. The Static Satisfaction data provider and the Percent Satisfied element provides the data your require.

  1. Right click on Simple_Cov () in the Object Browser.
  2. Select Report & Graph Manager... ().
  3. Select the Percent Satisfied () report in the Installed Styles list.
  4. Click Generate....
  5. Scroll to the bottom of the report.
  6. Note the % Satisfied.

    7. Downloading data directly through the Imager satellites to the ground site, you are able to cover approximately 46% of the Continental United States.

  7. Close () the Percent Satisfied report when finished.
  8. Close () the Report & Graph Manager when finished.

Changing Coverage Assets

You computed coverage using Direct_Connection () and determined that only 46 percent of the Continental United States is seen by your Imager cameras when downloading the data directly to the ground site. Determine the percentage of coverage when transmitting the data to a Relay satellite which has access to the ground site.

  1. Open US_Cov's () properties ().
  2. Select the Basic - Assets page.
  3. Select Direct_Connection () in the Assets list.
  4. Click De-assign.
  5. Select Indirect_Connection () in the Assets list.
  6. Click Assign.
  7. Click OK. STK will automatically recompute your coverage.
  8. Look at the 2D and 3D Graphics windows.

    9. Indirect Simple Coverage

    You still don't have 100% coverage, but visually you can see that coverage has improved. By how much?

Determining Indirect Coverage Percent Satisfied

Direct coverage gives you approximately 46% of coverage over the Continental United States. Using the Relay satellites, how much improvement do you get?

  1. Right click on Simple_Cov () in the Object Browser.
  2. Select Report & Graph Manager... ().
  3. Select the Percent Satisfied () report in the Installed Styles list.
  4. Click Generate....
  5. Scroll to the bottom of the report.
  6. Look at the % Satisfied.

    7. Transmitting data to a Relay satellite and then to the ground site, you are able to cover approximately 72 percent of the Continental United States.

Saving your work

  1. Close any open reports, tools and properties.
  2. Save () your work.

Summary

You are designing a constellation of imaging satellites that will provide imagery of the Continental United States. There is no internal storage on the satellites, so you need to download near-real-time data from the satellites to a ground station. Your analysis takes place during a 24 hour period. The cameras on your satellites have a 20 degree field of view (10 degree half angle).

Your first analysis was based on a direct connection between the Imager satellites and the ground site. In order to download the data, the camera passes the data to the parent satellite (Imager) which must have access to the ground site at the same time. You set this up using a Chain () object. Using a Coverage Definition () object and assigning the direct connection Chain () object as the asset, you determined through Simple Coverage that using the direct connection provided approximately 46% of coverage over the Continental United States.

Your second analysis was based on an indirect connection between the Imager satellites and the ground station. In this analysis, you set up a Chain () object that passed the data from the Imager satellites to any of the Relay satellites that had access at the same time with the ground station. Changing your asset to the indirect connection Chain () object improved your coverage to approximately 72%; a 26% improvement.