Digital Mission Engineering (DME): Constellation Design and Coverage (Part 1 of 4)

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

This lesson requires version 12.7 of the STK software or newer to complete.

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.

Capabilities covered

This lesson covers the following capabilities of the Ansys System Tool Kit® (STK®) digital mission engineering software:

  • STK Pro
  • Coverage
  • STK SatPro
  • STK Analyzer
  • STK Analyzer Optimization

Problem statement

Across the industry, the digital engineering process is becoming more complex. Systems of systems are changing and updating in different stages of the mission life cycle. In this series, you will address these challenges by creating a fully connected digital thread with a common mission environment at the core. You will design and test a new satellite constellation for persistent stereo coverage of hypersonic vehicles across the world. You will address this topic in stages: satellite constellations, hypersonic flight, EOIR sensors, communications links, and triggering events and systems. The vision is to integrate the mission environment and operational objectives into the digital thread early and throughout the entire product life cycle. Through digital mission engineering, you are now capable of quickly evaluating the overall mission impact of the smallest change to any component. This session will focus on the concept development phases using the STK software's Analyzer capability to conduct trade studies on the constellation geometry and optimizing based on system requirements.

Solution

In this first section of the DME series, you will focus on satellite constellation design using the STK software's Analyzer and Coverage capabilities. The goal in this exercise is to understand how to maximize the level of coverage with a global network of satellites. The main components you will analyze are the revisit time, which can be considered gap time, and the number of assets that have visibility to the ground. Using Analyzer's trade study capabilities, you can vary parameters of your system to find an ideal configuration.

What you will learn

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

  • Build a constellation of satellites using the Satellite Collection object
  • Build a Coverage analysis
  • Design relevant Figure of Merit quality metrics
  • Become familiar with the Analyzer capability’s workflow
  • Understand constellation design configurations
  • Load in an external results file

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 scenario and then build from there.

  1. Launch the STK application ().
  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 ImagingConstellation
    Start 13 Feb 2025 16:00:00.000 UTCG
    Stop + 1 day

    Using the precomputed trade study saves a half hour or more in your analysis and requires the Start and Stop time above. However, you can use the default scenario start and stop time if you want to design your own trade studies, which is more realistic.

  4. Click OK when you finish.
  5. Click Save () when the scenario loads. The STK application creates a folder with the same name as your Scenario for you.
  6. Verify the scenario name and location in the Save As dialog box.
  7. Click Save.

Save () often during this lesson!

Downloading required files

If you plan on completing your own trade study, you can skip to Inserting a Satellite Collection object. If you are going to use the precomputed trade study, you will need to download following the steps below.

  1. Download the zipped folder here: https://support.agi.com/download/?type=training&dir=sdf/help&file=DME_Part1_TradeStudy.zip

    If you are not already logged in, you will be prompted to log in to agi.com to download the file. If you do not have an agi.com account, you will need to create one. The user approval process can take up to three (3) business days. Please contact support@agi.com if you need access sooner.

  2. Navigate to the downloaded folder.
  3. Right-click on DME_Part1_TradeStudy.zip.
  4. Select Extract All... in the shortcut menu.
  5. Set the Files will be extracted to this folder: path to be within your scenario folder (e.g. C:\Users\username\Documents\STK 12\ImagingConstellation\DME_Part1_TradeStudy).
  6. Click Extract.
  7. Go to your scenario folder.
  8. The DME_OptStudy3.tstudy file will be in the DME_Part1_TradeStudy folder.

Using a Walker-type Satellite Collection

The Satellite Collection object models a group of satellites as a single object in the Object Browser. The associated satellites do not appear in the Object Browser, but are available for analysis purposes within other computational tools such as the STK software's Coverage capability, CommSystem objects, the Deck Access tool, and the Advanced CAT tool.

Inserting a Satellite Collection object

Start by inserting a Satellite Collection object into your scenario.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select SatelliteCollection () in the Select An Object To Be Inserted list.
  3. Select Insert Default () in the Select A Method list.
  4. Click Insert. . ..
  5. Right-click on SatelliteCollection1 () in the Object Browser.
  6. Select Rename in the shortcut menu.
  7. Rename SatelliteCollection1 () Walker_Collection.

Setting the Walker type subset

The Walker selection provides a constellation of satellites distributed in a series of altitude shells. Each shell contains evenly spaced orbital planes and Walker populates each orbital plane with evenly spaced satellites. All the satellites in a shell have the same period and inclination. Walker evenly spaces the ascending nodes of the orbital planes over a range (angle spread) of right ascensions (RAAN). You can generate multiple shells within a single Satellite Collection object.

  1. Right-click on Walker_Collection () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Definition page when the Properties Browser opens.

    4. You can see that Walker is selected as the default Type.

  4. Select Shells - Name - 1 in the Walker Properties panel.
  5. Click Edit selected shell () in the Shells toolbar.
  6. Enter Walker Group in the Shell Name field when the Edit Shell dialog box opens.
  7. Set the following options in the order shown in Shell Properties panel:
    8. Option Value
    Inter Plane Phase Increment 0
    Planes 1
    Satellites in Planes (Slots) 1
  8. Set the following parameters in the Plane 1 : Slot 1 panel:
    9. Option Value
    Semi-Major Axis (a) 6880 km
    Inclination (i) 50 deg
  9. Click Save Changes to apply your changes and to close the Edit Shell dialog box.
  10. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the subset marker size

You can control the graphical display of a satellite collection. The Satellite Collection Graphics Attributes cover both the 2D and 3D Graphics window attributes.

  1. Select the Graphics - Attributes page.
  2. Double-click in the AllSatellites - Marker Size cell.
  3. Enter 10 as the Marker Size value.
  4. Click OK to accept your changes and to close the Properties Browser.

Using a Coverage Definition object

You are now ready to model a coverage analysis over the Earth using a Coverage Definition object. The Coverage capability enables you to analyze global or regional coverage provided by one or more assets while considering all access constraints. A Coverage Definition object enables you to define and maintain an area of coverage, to define the objects providing coverage for the area, and to calculate accesses to the region.

Inserting a Coverage Definition object

Start by inserting a Coverage Definition object using the Define Properties method.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select Coverage Definition () in the Select An Object To Be Inserted list.
  3. Select the Define Properties () method in the Select A Method list.
  4. Click Insert. . ..

Changing the grid area of interest and point granularity

Coverage analyses are based on the accessibility of assets (objects that provide coverage) and geographical areas. The combination of the geographical area, the regions within that area, and the points within each region is called the coverage grid. The statistical data computed during a coverage analysis are based on a set of locations, or points, which span the specified grid area of interest. Points have specific geographical locations, and the STK software uses them in the computation of asset availability. The angular distance between the grid points is called the point granularity.

Use the Grid properties to define the location of your coverage grid to fall between specified minimum and maximum latitude bounds, with a point granularity that balances for accuracy and computation time.

  1. Select the Basic - Grid page in the Properties Browser.
  2. Enter 60 deg in the Max. Latitude field in the Grid Area of Interest panel.
  3. Enter 10 deg in the Lat/Lon field in the Point Granularity panel located in the Grid Definition panel.
  4. Click Apply to accept your changes and to keep the Properties Browser open.

Specifying the coverage assets

Assets properties enable you to specify the STK objects used to provide coverage. In this case, you want to use all of the satellites in the Satellite Collection. For all Satellite Collection objects, the STK software automatically generates a subset named AllSatellites that contains all members of the collection. Assign this subset to your Coverage Definition object.

  1. Select the Basic - Assets page.
  2. Expand () Walker_Collection () in the Assets list.
  3. Select the AllSatellites () Satellite Collection subset.
  4. Click Assign.
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Clearing Automatically Recompute Accesses

The STK software automatically recomputes accesses every time you update an asset on which the coverage definition depends, such as your Satellite Collection object. If you want to control when the STK software computes coverage, you need to turn this option off.

  1. Select the Basic - Advanced page.
  2. Clear the Automatically Recompute Accesses check box.
  3. Click OK to accept your changes and to close the Properties Browser.
  4. Rename CoverageDefinition1 () CoverageDefinition.

Using the Compute Accesses tool

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

  1. Right-click on CoverageDefinition () in the Object Browser.
  2. Select the CoverageDefinition shortcut menu.
  3. Select Compute Accesses in the CoverageDefinition submenu.

Generating a Percent Coverage graph

Now that you have set up and computed the coverage analysis, you can examine the quality of the coverage. But before you do that, take a quick look at the quality of the system you set up. One way to do that is to generate a Percent Coverage graph. This graph tells you how well the satellite in the Walker Collection is able to cover the Earth throughout the scenario time period.

  1. Select the Analysis menu.
  2. Select Report & Graph Manager... ().
  3. Open the Object Type drop-down list.
  4. Select CoverageDefinition.
  5. Select CoverageDefinition () in the Object Type list.
  6. Select the Percent Coverage () graph in the Styles list inside the Styles panel.
  7. Click Generate. . . . Your results may vary based on the default time of your scenario.

    8. Percent Coverage graph

    Take a look at how the current coverage stays low throughout the analysis period, but how the accumulated coverage increases over time. This gives you an idea of how well a single satellite can cover the region. You can understand this further with a Figure of Merit object.

  8. Close the percent coverage graph and the Report & Graph Manager.

Designing the coverage definition Figures of Merit

You set up the problem using a Coverage Definition object. The STK software enables you to specify the method by which the quality of coverage is measured using a Figure Of Merit object. You can attach FOM objects to a Coverage Definition object; they provide the means for evaluating the quality of coverage provided by Coverage Definition's assigned objects (or assets).

In this study, you will focus on two parameters: the Number of Assets (N Asset Coverage) and the Revisit Time. The mission requirements state you must have at least two assets covering every grid point at all times.

Inserting an N Asset Figure of Merit object

An N Asset FOM determines how many different assets are simultaneously covering each individual grid point at each time in the analysis period.

You can specify that the FOM compute the minimum value from the set of all grid points to make sure all grid points are at or above that threshold.

  1. Insert a Figure of Merit () object using the Define Properties () method.
  2. Select CoverageDefinition () in the Select Object dialog box.
  3. Click OK.

Setting the N Asset coverage definition

You want to measure if at least two satellites simultaneously cover every single point in the coverage analysis.

  1. Select the Basic - Definition page in the Properties Browser.
  2. Open the Type drop-down list in the Definition panel.
  3. Select N Asset Coverage.
  4. Open the Compute drop-down list.
  5. Select Minimum.

    6. Using Minimum calculates the minimum number of assets available over the entire coverage interval.

Selecting the N Asset FOM satisfaction criteria

You can restrict the FOM's behavior so that the STK software only applies the graphical properties of the FOM when a chosen satisfaction criterion is met.

  1. Select the Enable check box in the Satisfaction panel.
  2. Open the Satisfied if drop-down list.
  3. Select At Least.
  4. Enter 2 in the Threshold field.

    5. The FOM value is greater than or equal to the Threshold.

  5. Click OK to accept your changes and to close the Properties Browser.
  6. Rename FigureofMerit1 () NAsset.

Inserting the revisit time Figure of Merit object

Now that the coverage has a threshold of at least two satellites per grid point, you can set up revisit or gap time.

  1. Insert a Figure of Merit () object using the Define Properties () method.
  2. Select CoverageDefinition () in the Select Object dialog box.
  3. Click OK.

Defining the revisit time coverage definition

Revisit time (gap time) measures the intervals during which coverage is not provided. You want to minimize the gap time so that the maximum value satisfies the requirements with a zero-second gap time.

  1. Select the Basic - Definition page in the Properties Browser.
  2. Open the Type drop-down list in the Definition panel.
  3. Select Revisit Time.
  4. Enter 2 in the Min # Assets field.

    5. Min # Assets specifies the minimum number of simultaneous assets that are required for coverage.

  5. Keep the Compute and End Gaps set as their default selections.

    6. Compute: Maximum specifies that the computed value is the duration of the longest gap in coverage over the entire coverage interval.

    End Gaps is set to Include to have gaps at the ends of the analysis interval included in the revisit time computations.

Selecting the revisit time FOM satisfaction criteria

You will use the At Most Satisfaction Criteria. Using At Most, the FOM value is less than or equal to the Threshold.

  1. Select the Enable check box in the Satisfaction panel.
  2. Open the Satisfied if drop-down list.
  3. Select At Most.
  4. Leave the default Threshold value of 0 sec.
  5. Click OK to accept your changes and to close the Properties Browser.
  6. Rename FigureofMerit2 () RevisitTime.

At this point, you might be wondering why you're setting up both FOMs to use a minimum of two satellites when you currently have one satellite in your collection. When you use Analyzer, you will set it up so that there are six orbital planes with six satellites per plane.

Using Analyzer for trade studies

The Analyzer capability provides a set of analysis tools that:

  • Enable you to understand the design space of your systems.
  • Allow you to perform analyses in the STK application easily without involving programming or scripting.
  • Introduce trade study and post-processing capabilities.

Analyzer tools can be used with all STK scenarios, including those with satellites propagated using the STK/Astrogator® capability.

Setting up your analysis

You are now ready to dive into some trade study analysis using Analyzer. You can build a simple example and then load the results into a more complex study. The goal is to become familiar with the Analyzer workflow, as well as loading results of previously run analyses.

  1. Select Analyzer in the Analysis menu.
  2. Select Analyzer... () in the Analyzer submenu.

Analyzer may open behind the STK application window. Arrange your workspace so you are able to access Analyzer.

Defining the input variables

You need to select input and output variables from the main Analyzer window to pass to the Parametric Study tool. Start by adding the input variables to Analyzer.

  1. Select Walker_Collection () in the scenario tree.
  2. Select Walker () in the General tab of the STK Property Variables panel.
  3. Move () Walker () to the Analyzer Variables list.

Defining the output variables

Now that the input variables are defined, you can add the output variables. The output variables are the variables you'd like to solve for. You want to solve for Minimum N.Asset Overall and Maximum Revisit Time Overall.

  1. Expand () CoverageDefinition () in the scenario tree.
  2. Select NAsset ().
  3. Expand () the Overall Value () directory in the Data Providers () tab in the Data Provider Variables panel.
  4. Select Minimum ().
  5. Move () Minimum () to the Analyzer Variables list.
  6. Select RevisitTime () in the STK Variables list.
  7. Expand () the Overall Value () directory in Data Provider Variables panel.
  8. Select Maximum ().
  9. Move () Maximum () to the Analyzer Variables list.

Using the Parametric Study Tool

The Parametric Study Tool runs a model through a sweep of values for some input variable. The resulting data can be plotted to view trends.

Specifying the variables

To perform a Parametric Study, one design variable and one or more responses must be specified. For the design variable, a starting value, an ending value, and the number of steps must be specified.

  1. Click Parametric Study... () on the Analyzer toolbar to open the Parametric Study Tool.
  2. Click and drag SemiMajorAxis () from the Component Tree on the left to the Design Variable field on the right when the Parametric Study Tool opens.
  3. Set the following options for the Design Variable:
    4. Option Value
    starting value 6880
    ending value 7680
    step size 100

    These settings will vary the semi-major axis in 100-kilometer increments. It will take a total of nine runs to complete the trade study.

  4. Click and drag the following variables from the Component Tree to the Responses list:
    • NAsset - Minimum
    • RevisitTime - Maximum

Defining the Walker variables

Define the walker parameters within the parametric study.

  1. Locate the Walker - Shell_Walker_Group list, located in the Components list. To the right of each variable is a value that you can click to change the value.
  2. Set the following options for the Walker Constellation:
    3. Option Value
    Planes 6
    SatellitesInPlanes 6

Running the parametric trade study

This parametric trade study will take a few minutes to run.

  1. Click Run. . ..
  2. When the analysis is complete, examine the results.

    3. In each of the runs, you should see the revisit time (gaps) decrease as the semi-major axis increases. Eventually it goes to zero. The average increases to two for the number of assets. The minimum number of assets eventually reaches two.

Generating a 3D Scatter Plot

There are a few ways to view the data. One interactive way to view the data is with a 3D Scatter Plot. A 3D Scatter Plot displays an x-y plot of variables in the model.

  1. Bring the Data Explorer view to the front.
  2. Click Add View in the Data Explorer toolbar.
  3. Select 3D Scatter Plot in the shortcut menu.

Modifying the 3D Scatter Plot

Use the dimensions menu to change which variable is displayed on which axis.

  1. Click Dimensions.
  2. Set the following options:
    3. Option Value
    X Maximum
    Y Minimum
    Z SemiMajorAxis
  3. Click the graph to close the Dimensions window.

Reviewing the 3D Scatter Plot

Examine the matrix.

  1. Click any point to get information about that run.
  2. Note the semi-major axis of the last run (7680 km). This gives you the requirements you are looking for: 2 assets with 0 seconds revisit time.

    3. Analyzer 3D Scatter plot

  3. Close the 3D Scatter Plot window.
  4. Close the Data Explorer Window.
  5. Click No to close your trade study without saving.

Syncing the results of your parametric study to the STK application

All of the criteria meet in the final run (semi-major axis 7,680 km); however, remember that the semi-major axis values are raised in 100-kilometer increments. There is likely a minimum semi-major axis that enables you to achieve your goals sooner. If you consider cost, which might be tied to a higher orbit, you can find a lower semi-major axis that also reduces cost.

Push the results of a single run to the STK application and examine the scenario.

  1. Return to the Parametric Study Tool.
  2. Set the SemiMajorAxis () Value to 7680 in the Components list. You do not need to enter units.
  3. Click Sync to STK.

    4. This pushes the results of your trade study to the STK application. It may take a few minutes to insert and configure the satellites.

  4. Close the Parametric Study tool when the coverage analysis is complete.
  5. Minimize Analyzer.
  6. Look at the 2D and 3D Graphics windows.

    7. Walker_Collection () is automatically updated from the last run and the Walker Group now contains six planes, six satellites per plane, and all the satellites are at a semi-major axis of 7,680 kilometers.

Examining the Data

Now that you have a result loaded in, look at some of the reports and graphs in the STK application that can shed some light on the scenario.

  1. Right-click NAsset () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Percent Satisfied () report in the Installed Styles directory when the Report & Graph Manager opens.
  4. Click Generate. . ..
  5. Scroll to the bottom of the report and look at the % Satisfied column.

    6. You should have 100% coverage, which means you have a minimum of two satellites with access to a point on the ground. The Percent Satisfied report confirms that information.

  6. Close the Percent Satisfied report.
  7. Select the Grids Stats Over Time () report in the Installed Styles directory.
  8. Click Generate. . . .
  9. Scroll through the report.

    10. You can see that you meet the minimum, but you have a few locations that have up to five or six satellites with access (depending on the analysis period). This creates a lot of redundancies, so you can start thinking of optimizing the setup.

    You have two options at this point:

    • Continue to test configurations using parametric scans, carpet studies, and design of experiments.
    • Optimize the scenario to find the optimal semi-major axis.

    You may also consider if you need to change other factors with the study (number of satellites or planes).

  10. Close any reports and the Report & Graph Manager when finished.

In the upcoming procedures, you have the option of loading a precomputed trade study or setting up and running the trade study yourself. The precomputed optimization trade study took approximately an hour to run. If you want to use the precomputed trade study, start at the Loading in a precomputed optimization study section. If you want to set up and run the trade study manually, skip to the Performing an Optimization Study section.

Loading in a precomputed optimization study

The study you will load in was run for approximately an hour using the Satellite Collection object. Older versions of the STK software required the use of the Walker Tool and individual Satellite objects, which took upwards of 10 hours to analyze. The goal is to minimize the semi-major axis and the total number of satellites. At the same time, you want to minimize the revisit time (no gaps) and have two satellites maintain access with a point on the ground.

Opening the precomputed trade study

Load in the data from the precomputed trade study and examine it.

  1. Select Analyzer in the Analysis menu.
  2. Select Open Trade Study Result... in the Analyzer submenu.
  3. Browse to the location of the precomputed trade study you extracted earlier (e.g. C:\Users\username\Documents\STK 12\ImagingConstellation\DME_Part1_TradeStudy).
  4. Select DME_OptStudy3.tstudy.
  5. Click Open.

    6. This opens the trade study results table and graph.

Understanding the results

View the results in the precomputed trade study's 3D Scatter Plot.

  1. Examine the results in the 3D Scatter Plot window.

    2. You can see the configurations that met the criteria in blue and those that didn't in gray.

    Analyzer 3D Scatter plot

  2. Click any point in the graph to see more information about a run.
  3. Select the lowest blue point on the graph.

    4. This is the lowest semi-major axis that satisfies all of your criteria (7637.60 km).

  4. Examine the table.

    5. You can scroll to see all the runs that were conducted and each result. You also have the option to export the data into Excel or another tool for post-processing.

  5. Scroll to run 191.

    6. This is the run that met all of the criteria of the trade study.

If you want to run the trade study yourself, proceed to the Performing an Optimization Study section. Otherwise, skip to Syncing the results to the STK application using the precomputed trade study section.

Performing an Optimization Study

Looking at the data, there is a clear point that meets all the conditions for the study. Use the Optimization Tool to get an idea of the workflow. The Optimization Tool is a collection of optimization algorithms that can be used within the Analyzer capability.

This is an additional section for users who would like to set up an optimization themselves.

Syncing data from the STK application

First, load in the best result from the available data.

  1. Close the 3D Scatter Plot window.
  2. Close the Data Explorer window.
  3. Click No to close your trade study without saving.
  4. Select Analyzer in the Analysis menu.
  5. Select Optimization Tool... () in the Analyzer submenu.
  6. Click Sync from STK. This loads the current setup in the scenario to the Optimization Tool.

Defining the optimization objective

To perform an Optimization Study, an objective function and a least one design variable must be specified. The objective functions can be specific variables or equations composed of multiple output variables. For each objective, you must specify whether you want to minimize or maximize the objective or find a design where the objective has as specific value. Your current objective is to minimize the semi-major axis while meeting the coverage criteria.

  1. Click and drag SemiMajorAxis () from the Component Tree to the Objective list located in the Objective Definition panel.
  2. Ensure the Goal is set to minimize.

Defining the constraints

Constraints restrict particular variables to a region or value, that is, a bound specified in the list of constraints prevents a design point The highest corrected flow of an engine at inlet to the compression system. from being found that causes that output variable to occur outside the specified region. For this optimization, you want to minimize the number of satellites that will provide coverage without any gaps.

  1. Click and drag NAsset - Minimum from the Component Tree to the Constraint list located in the Objective Definition panel.
  2. Set the Lower Bound to 2.
  3. Click and drag Revisit Time - Maximum from the Component Tree to the Constraint list.
  4. Set the Lower and Upper Bounds to 0.

Each constraint must have either an upper or lower bound, but can also have both. Constraints can also be equations composed of multiple variables.

Defining the SemiMajorAxis design variable

The design variables are the variables that the optimizer will modify to meet the objective. You must enter the bounds between which the optimizer is allowed to set the design variables. For continuous variables, like the semi-major axis, these bounds are required.

  1. Click and drag SemiMajorAxis () from the Component Tree to the Design Variable list located in the Design Variables panel.
  2. Set the following Lower and Upper bounds:
    3. Option Value
    Lower Bound 7580
    Upper Bound 7680

Defining the number of satellites per plane

Optimize for the number of satellites per plane. Both the start and end values must be specified for the number of satellites, which is defined by an integer value. The start and end values are used to create the enumeration for the integer; all integer values between the start and end values are used.

  1. Click and drag SatellitesInPlanes () from the Component Tree to Design Variable list.
  2. Set the following options in the dialog box:
    3. Option Value
    Start Value 3
    End Value 6
  3. Click OK to confirm your selection and to close the dialog box.

Defining the number of planes

Like the SatellitesInPlanes variable, the number of planes is also an integer value.

  1. Click and drag Planes () from the Components list to the Design Variable list.
  2. Set the following options in the dialog box:
    3. Option Value
    Start Value 3
    End Value 6
  3. Click OK to confirm your selection and to close the dialog box.

Selecting an algorithm

There are over 30 algorithms to choose from when using the Optimization Tool. You will use the Darwin Algorithm. Darwin is a genetic search algorithm developed specifically for solving engineering optimization problems. Because the Darwin algorithm does not require gradient information, it is able to effectively search non-linear and noisy design spaces. Also, Darwin is a genetic optimizer that can solve constrained design problems.

  1. Select Darwin Algorithm in the Algorithm drop-down list.
  2. Click Run.

    3. Be patient. This will take a long time (potentially an hour or more depending on your PC).

Understanding the results

If you loaded the downloaded trade study, the values may be different due to your analysis period. However, it should be close. The image that follows will probably be different than your results but it should also be close.

  1. When the trade study is finished, bring the Optimization Tool to the front.
  2. Click View Output..., located in the lower right corner.
  3. Select the Best Design tab when the Optimization Tool Results window opens.

    4. Best Design

    You should get similar results to those of the precomputed trade study. The best design run number might be different from the image. That's OK. At the top of the Optimization Tool Results window, it will tell you the best design run number. All the values on the right of the dialog box shows you the best values.

  4. Bring the Data Explorer window to the front.
  5. Scroll to the Best Design Run Number column.

    6. This data will be the same as the values seen in the Optimization Tool Results - Best Design tab.

  6. Skip to the Syncing the results to the STK application using your trade study section.

Syncing the results to the STK application using the precomputed trade study

Use the following steps if you used the precomputed trade study. Out of the runs that met all the criteria of the trade study, run 191 had the lowest semi-major axis (7,637.60 km).

  1. Select Analyzer in the Analysis menu.
  2. Select Optimization Tool... () in the Analyzer submenu.
  3. Ensure the following values are set in the Components list:
    OptionValue
    Planes6
    SatellitesInPlanes6
  4. Set the SemiMajorAxis to 7637.60 km in the Components list. You do not need to enter units.
  5. Click Sync to STK. This pushes the results to your STK scenario.
  6. Skip to the Examining the data section.

Syncing the results to the STK application using your trade study

Use the following steps if you ran your own trade study.

  1. Bring the Optimization Tool to the front.
  2. The value showing for SemiMajorAxis () should match the best design value. If not, enter the value manually.
  3. Click Sync to STK. This pushes the results to your STK scenario.

Examining the data

Now that you have a result loaded in, look at some of the reports and graphs in STK that can shed some light on the scenario.

  1. Bring the STK application to the front.
  2. Right-click on NAsset () in the Object Browser.
  3. Select Report & Graph Manager... () in the shortcut menu.
  4. Select the Percent Satisfied () report in the Installed Styles directory.
  5. ClickGenerate. . ..
  6. Scroll to the bottom of the report.

    7. You know from the results of the trade study that this configuration enables you to have a minimum of two satellites with access to a point on the ground. This report confirms that you have 100% Satisfaction.

  7. Close the Percent Satisfied report.

Graphing the results

Create a grid stats over time graph to evaluate your optimization.

  1. Return to the Report & Graph Manager.
  2. Select the Specify Time Properties option in the Time Properties panel.
  3. Select the Use step size / time bound option.
  4. Enter 1 sec in the Step size field.

    5. By reducing the step size to one second, the graph will show more information.

  5. Select the Grid Stats Over Time () graph in the Installed Styles directory.
  6. Click Generate. . ..

    7. Grid stats over time graph

    From these data, you can see that you have full coverage throughout your mission. The minimum criterion of two satellites with simultaneous access to a grid point is met. This is confirmed in the Percent Satisfied Report and the Grid Stats Over Time graph. You can also see that you have a maximum of four to six satellites with simultaneous access to a grid point. This redundancy is key in case you lose a satellite in the course of a mission.

    The objective to create a new satellite constellation that provides persistent, stereo coverage of hypersonic vehicles across the world has been met.

Saving your work

Clean up your workspace and close out your scenario.

  1. When finished, close all tools, graphs and reports you still have open.
  2. Save () your work.

Summary

You have the results of the optimization run, but there are many parameters that you can vary in the analysis. The flexibility of the STK software and the Analyzer capability enables you to change an aspect of the mission (like the semi-major axis) while knowing that it carries through and is used in all calculations. If you have access to the Ansys ModelCenter® model-based systems engineering software, you can link your analysis with ModelCenter using the STK ModelCenter Plugin and incorporate cost breakdowns, the total number of satellites, and other parameters. You can thus integrate the mission earlier and take into consideration all of the factors in the mission environment.

DME Lesson 2: Hypersonics and EOIR

The next lesson in the DME series focuses on Hypersonics and EOIR. You will use a starter scenario and build your own hypersonic vehicle. You will use an EOIR sensor to image it. This leads up to sessions three and four of the DME series where you bring the constellation from this lesson and the flight from session two together to understand how all components for the mission works together.