Part 18: Assessing the Threat of a Collision

This training requires additional licenses to complete. You can obtain the necessary license for the training by visiting http://licensing.agi.com/stk/evaluation or calling AGI support.

Space Situational Awareness and Conjunction Analysis Tool (CAT)

There are tens of thousands of space objects orbiting Earth every day, which makes for a pretty crowded highway for your satellite. It is important to assess any potential collisions during launch, and while in orbit, to ensure the safety of your mission assets. STK provides the tools to model and analyze the up-to-date locations of most of the entire space catalog, allowing operators to analyze the likelihood of collisions in orbit.

The Space Data Center used AGI's software to reduce radio frequency interference (RFI) geolocation uncertainty by up to two orders of magnitude. You can read more in this case study: SDA's Space Data Center Enables Fast, Accurate RFI Geolocation and Conjunction Analysis.

The Advanced CAT tool provides a convenient way for you to carry out close approach analysis for multiple satellites and two-line element (TLE) sets. After applying user-selected filters, Advanced CAT performs close approach analyses between primary objects (e.g. satellites owned by or otherwise of interest to the user) and secondary objects (those presenting a risk of collision), with reference to a threshold - a minimum acceptable distance - between the ellipsoidal threat volumes of the objects.

Update the Satellite Database, Model a Satellite, and Identify Potential Threats

It is important to ensure that you have the most up-to-date satellite data before performing the analysis.

Watch the following video, then follow the steps below incorporating the systems and missions you work on (sample inputs provided).

  1. Create a new scenario with the default time period.Closed
    1. Click the Create a new scenario () button.
    2. In the New Scenario Wizard, set the following options:
      • Enter a name for the scenario (e.g. STK_CAT).
      • Define the analysis stop time to be two days after the start time.
    3. Click OK.
  2. Use the Data Update Utility to update the satellite database.Closed
    1. Extend the Utilities menu and select Data Update...
    2. Select Update beside the satellite database Data set.
    3. Click the Update Now button.
    4. Click OK to dismiss the Data Update Utility.
  3. Restart STK () to use the updated satellite database.Closed
    1. Save () your work.
    2. Extend the File menu and select Open ().
    3. Navigate to your scenario (e.g "STK_CAT") and open it.
  4. Insert an active Earth observation satellite () from the Standard Object Database (examples below).Closed
    1. Online ()Closed
      1. Select Satellite in the Insert STK Objects () tool.
      2. Select the From Standard Object Database as the Select A Method option.
      3. Click Insert.. to bring the Standard Object Database to the front.
      4. Select the Online tab.
      5. In the Name or ID text field, enter a Satellite Name or ID (e.g. Worldview) or select Earth Observation from the Mission drop-down list and Operational from the Operational Status drop-down list.
      6. Click Search. The matching satellites are shown in the Results field.
      7. Select the corresponding result (e.g. CommonName = Worldview-2) from the list.
      8. Click Insert.
      9. Click Close to dismiss the Satellite Database window.
    2. LocalClosed
      1. Select Satellite in the Insert STK Objects () tool.
      2. Select the From Standard Object Database as the Select A Method option.
      3. Click Insert.. to bring the Standard Object Database to the front.
      4. Select the Local tab.
      5. In the Name or ID text field, enter a Satellite Name or ID (e.g. Worldview) or select Earth Observation from the Mission drop-down list and Operational from the Operational Status drop-down list.
      6. Click Search. The matching satellites are shown in the Results field.
      7. Select the corresponding result (e.g. CommonName = Worldview-2) from the list.
      8. Click Insert.
      9. Click Close to dismiss the Satellite Database window.
  5. Right-click on the Satellite () in the Object Browser and select Zoom To.
  6. Identify Potential Threats to your primary satellite (e.g. Worldview-2) from the contents of the entire public catalog of tracked space objects.
  7. Insert an AdvCAT () object using the Define Properties method.Closed

      8. You may need to add the Advanced CAT object to the Insert STK Objects tool. To do this, click the Edit Preferences button and select it from the New Object tool.

    1. Select AdvCAT () in the Insert STK Objects () tool. If you don't see the AdvCAT object, click the Edit Preferences... button to add it to the Insert STK Objects tool.
    2. Select the Define Properties as the Select a Method option.
    3. Click Insert... to bring the Properties Browser to the front.
  8. In the grid beside the Defaults field for the primary and secondary assets, enter the desired values for the Tangential, Cross Track, and/or Normal dimensions of the object's threat volume..
  9. Enter the desired threshold value in the Threshold text box (e.g. 10 km). This is the threshold distance between the error ellipsoids that constitutes a potential conjunction.
  10. Select the Primary Satellite list.Closed
    1. Select the Primary satellite (e.g. Worldview-2) in the Available Primary list.
    2. Click the Insert () button to add it to the Chosen list. You can add more than one satellite or database to the Primary list.
  11. Select the Secondary Satellite list.Closed
    1. Select the entire public catalog of tracked space objects (stkAllTLE.tce) in the Available Secondary List.
    2. Click the Insert () button to add it to the Chosen list. You can add more than one satellite or database to the Secondary list.
  12. Click the Compute button in the AdvCAT object's Properties to compute the conjunctions.
  13. View any conjunctions between your primary and secondary satellites.Closed
    1. Click Reset () on the animation toolbar to view the error ellipsoids in the 3D Graphics window.
    2. Generate a Close Approach by Min Sep report using the Report & Graph Manager.
      1. Click the Report & Graph Manager () icon or extend the Analysis menu and select Report & Graph Manager.
      2. In the Object Type drop-down list, select AdvCAT.
      3. Select the AdvCAT object for the report that will be generated.
      4. Expand () the Installed Styles directory and select Close Approach by Min Sep.
      5. Click Generate... to display the conjunctions sorted by minimum separation.
    3. Visualize Conjunctions in the 3D Graphics Window.
      1. Right-click on one of the Time In lines, click to open the Time In menu, and select Set Animation Time.
      2. Bring the 3D Graphics window to the front and click Step Forward () on the animation toolbar to see the ellipsoids change color depending on their separation (e.g. red = ellipsoid intersection; yellow = ellipsoids are within the threshold; green = no conjunction).

If you want to know when a new satellite is added to the Satellite Database, subscribe to AGI's launch notification emailslaunch notification emails. These notifications are sent as soon as a new satellite has been identified and added to the database.

Primary objects are the satellites of interest to you. Primary objects may include satellites that you own or want to use. Secondary objects are those that present a potential risk of collision with, or approach closely, to your primary objects.

By default, close approach computations use the distance between the threat volumes or the user defined ellipsoids around the primary and secondary satellites as the criterion. If Range is selected, the close approach computation is performed using the range between the two objects as the criterion rather than the ellipsoid separation.

Don't forget to save your work!

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