Using the Time Tool

Overview

This tutorial will introduce STK’s Time Tool to analyze the response time of a Coast Guard Search and Rescue system. A disabled vehicle will issue a distress call, which is picked up by the NOAA Search and Rescue Satellite Aided Tracking (SARSAT) constellation. Once the call is confirmed, a rescue helicopter is dispatched to that location in a cascading series of events, one triggering the next.

STK Professional and Analysis Workbench. This tutorial is designed for STK users only.

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.

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

Create a Scenario and Establish the Distress Call

  1. Launch STK.
  2. Click the Create a Scenario button in the Welcome to STK dialog.
  3. Name the scenario “SARSAT_Response.”
  4. Change Start: to 1 Jul 2016 16:00:00.000 UTCG.
  5. Change Stop: to 2 Jul 2016 16:00:00.000 UTCG.
  6. From the Insert Object () tool, select the Target () object and the Define Properties () method. Click Insert…
  7. Leaving the target () Properties () window open to the Basic - Position page, arrange the windows such that you can see the 2D Graphics window. Click anywhere in a large body of water to move the target to that click location.
  8. Click OK to close the target () Properties ().
  9. Rename the target “DistressLocation.”
  10. From the Insert Object () tool, select the Satellite () object and the From Standard Object Database () method. Click Insert…

If you have an internet connection, the database tool pulls objects from the AGI Standard Object Database. This is a compilation of publicly available data about various platforms and their payloads. If you don't have an internet connection, the database tool defaults to the local installed database, which has positional data only. If an Internet connection is available, it will attempt to pull in the most recent position data available. Otherwise, it will use locally cached position data.

Insert the NOAA Satellites

  1. For Name or ID:, enter “NOAA,” then click Search.
  2. In the Results: field, click Common Name.
  3. Using Ctrl click, select NOAA 15, NOAA 18, and NOAA 19. Ensure you are selecting satellites from the “AGI’s Standard Object Data Service” Data Source.
  4. Enable the “Create Constellation from Selected ” option.
  5. In the Name field, enter “SARSAT.”
  6. Click the Insert button to import the constellation of satellites; then click Close.
  7. From the Insert Object () tool, select the Chain () object and the Define Properties () method. Click Insert…
    1. Select DistressLocation () target and move it () to the Assigned Objects list.
    2. Select the SARSAT () constellation and move it () to the Assigned Objects list.
    3. Click OK.
  8. Rename the chain “DistressCall.”
  9. Close the Insert Object Tool.

Using the Timeline View

Display the Access times from the Distress Call target to the SARSAT constellation on the Timeline View. The Timeline View is a display window that presents Time objects in a visual manner. The Timeline also provides another method to interact with the animation time by dragging the Time slider bar, or by right-clicking on the timeline or a time component to jump to that instant.

  1. On the Timeline, click the Add Time Components () button.
  2. In the Object selection window, select the DistressCall chain object and in the Component selection window select the CompleteChainAccessIntervals () component.

    3. If the DistressCall Chain is not visible, set the “Filter by” option to All STK Objects.

  3. Click OK. You will see the Complete Chain Accesses in the Timeline View.
  4. Move the DistressLocation target to a new location, using either the 3D Object Editor or opening the Properties and clicking the 2D Map, as described above. Notice the immediate change on the Timeline.

Creating and Using Time Components

Time components are built on two basic types: Instants and Intervals. An instant is any single moment in time (e.g. “Launch time”), whereas an Interval is a period of time bounded by two time Instants (e.g. “Launch Window”). In addition to those basic types, we also have

  • Interval list: A set of intervals, e.g. access intervals
  • Collection of Interval lists: A group of related interval lists, e.g. lighting intervals—Direct Sun, Umbra, and Penumbra intervals
  • Time Arrays: A set of time instants, e.g. threshold crossings, or Acquisition Of Signal times

Confirm the Distress Call

Due to the large number of false alarms received by the SARSAT satellites, rescue response is only sent after a second satellite pass confirms a distress signal. Create a new Time Interval to capture the second satellite pass, when the distress call is confirmed.

  1. Right click on the DistressCall Chain object and select Analysis Workbench ().
  2. Select the Time tab.
  3. Click the Create new Interval () button.
    1. Type: Interval From List
    2. Name: DistressConfirmed
    3. Interval List: On the left side, select the DistressCall chain. On the right, select CompleteChainAccessIntervals ().
    4. Interval Selection: Count forward from Start
    5. Interval Number: 2
  4. Click OK.
  5. Drag-and-drop the new DistressConfirmed () interval from the Analysis Workbench to the Timeline View.

Insert Helicopter Preparation Time

To compensate for the time it takes to contact and prepare a rescue helicopter, create a new Time Instant that is delayed 20 minutes after the time of the distress confirmation before launching the helicopter. The helicopter will take off after this delay.

  1. Click the Create new Time Instant () button.
    1. Type: Fixed Time Offset
    2. Name: RescueLaunchTime
    3. Reference Time Instant: Click the () button. Select the DistressCall chain on the left side; then on the right side, click the () button to expand the DistressConfirmed interval. Select Stop ().
    4. Time Offset: 20 min
  2. Click OK.
  3. Drag-and-drop the new RescueLaunchTime onto the Timeline View.
  4. Try moving the DistressLocation Target once again.

With each change to the scenario, the relationships between times are preserved and the entire set of time components update accordingly.

Launch the Rescue Helicopter

Use the new Time Instant to define the launch time of a new Rescue Helicopter flight.

  1. From the Insert Object () tool, and create a new Aircraft () using the Insert Default () method.
  2. Close the Insert Object tool.
  3. Rename the new aircraft “RescueHelicopter.”
  4. Select the 3D Graphics window.
  5. To define the route using the 3D Object Editing technique, first locate the 3D Object Editing toolbar:

    6. If the 3D Object Editing Toolbar is not shown, extend the View menu. Extend the Toolbars menu and then select “3D Object Editing.”

    1. Select Aircraft/RescueHelicopter from the 3D Object Editing drop-down.
    2. Click the Object Edit Start/Accept () button.
    3. Shift-click on the 3D Globe to add waypoints to the route. Enter a waypoint at the shoreline, and a waypoint at the DistressLocation.
    4. Click the Object Edit Start/Accept () button to save the changes to the route.
  6. Open the RescueHelicopter properties. On the Basic - Route page, click the down button () next to the Start and Stop field.
  7. Select Start Time, then Time Component…
  8. From the Select Time Instant dialog, on the left side, select the DistressCall chain, and on the right side, select the RescueLaunchTime instant.
  9. Click OK.
  10. Now the helicopter, instead of launching at the start of the scenario (default), will launch 20 minutes after the confirmation of the distress call. Furthermore, since the launch time depends on the distress call intervals, if those intervals change, the launch time will automatically update.

Show Position Updates

Create a new Interval List to determine when the RescueHelicopter might receive updates on the position of the DistressLocation as it approaches. This is accomplished by merging the DistressCall chain intervals with the RescueHelicopters flight interval.

  1. Open the Analysis Workbench, if it is not already open. Ensure that the DistressCall chain is selected on the left side. Click the Create new Interval List () button.
    1. Type: Merged
    2. Name: DistressPositionUpdates
    3. Operation: AND
    4. Remove the two Components in the Time Components section.
    5. Click the Add... button.
    6. Select the DistressCall () chain and CompleteChainAccessIntervals (). Click OK.
    7. Click the Add button.
    8. Select the RescueHelicopter () and EphemerisTimeSpan (). Click OK.
  2. Click OK.
  3. Drag-and-drop the new Interval List DistressPositionUpdates onto the Timeline View to display the result.

Summary

The Timeline View and the Time tool in the Analysis Workbench are a new way to interact with time in STK. In addition to displaying times and setting object start times, Time components can also form the basis of access constraints, report and graph intervals, object behaviors and display properties, and more.

If you do not have any DistressPositionUpdate intervals on the Timeline View, add the Aircraft's EphemerisTimeSpan to the Timeline View. In order for the RescueHelicopter to receive updates on the position of the DistressLocation as it approaches, the route needs to overlap with at least one of the Complete Chain Access Intervals. You can relocate the Target, DistressLocation, and modify RescueHelicopter's route so they overlap allowing time for the helicopter to get distress position updates. This will then display DistressPositionUpdate intervals.

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