Determining Magnetic Conjugacy with SEET

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.

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 STK Capabilities:

  • STK Pro
  • Space Environment and Effects Tool (SEET)

Problem Statement

You are an analyst for the DMSP satellite constellation. You need to determine the local magnetic vector location along the orbit and the times when the spacecraft is magnetically conjugate to your ground station. You will be modeling an event in 2016, so you will need to create an archive scenario.

Solution

Build a scenario that will model the DMSP satellite orbit of interest and a ground station of interest. Then use STK's Space Environment and Effects Tool (SEET) capability to model the geomagnetic conjugacy with respect to your objects of interest.

Break It Down

  • You will model an event between the dates of 1 Jul 2016 16:00:00.000 UTCG to 2 Jul 2016 16:00:00.000 UTCG.
  • You will model the DMSP 5D-3 F17D satellite.
  • You will use the IGRP model as the magnetic model.
  • You will display the Geomagnetic vectors and report the results.

Introduction

SEET's Magnetic Field component computes the full vector magnetic field along the satellite path, as well as performing field-line tracing, using standard models. Typically, the International Geomagnetic Reference Field (IGRF) is used to model the Earth main (core) field contribution. The IGRF is a multi-pole spherical harmonic approximation fit to measurements of the magnetic field produced by currents flowing beneath the Earth's surface. In addition, an external field model is provided to estimate the contribution of the solar-wind magnetic field to the near-Earth environment. Many spacecraft fly directional magnetometers to measure their local vector magnetic field (denoted as B by convention) which can, in combination with a suitable field model, be used for navigation or attitude control.

Another aspect of magnetic fields is the concept of “lines of force” or magnetic field-lines (such as the patterns produced in iron filings by a bar magnetic). The fieldlines play an important role in understanding the physics of the near-Earth space environment because high-energy charged particles that populate near-Earth space spiral along these field-lines. In this context, scientists are often interested in knowing when two points – such as a ground magnetometer station and a satellite – are connected by the same field line, a condition known as magnetic conjugacy.

Video Guidance

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

Create a Scenario

  1. Create a new scenario by using the New Scenario Wizard. You can also extend the File menu and select New...
  2. Rename the scenario SEET_MagneticConjugacy.
  3. Set the analysis period to the following:
    OptionValue
    Analysis Start Time1 Jul 2016 16:00:00.000 UTCG
    Analysis End Time2 Jul 2016 16:00:00.000 UTCG

Add a Satellite

Add a satellite to the scenario that exercises the Magnetic Field model in the desired manner and ensure the satellite transits a sun synchronous orbit at around 850 km altitude.

  1. Insert a new satellite using the following method:
    2. Option Value
    Select an Object to be Inserted: Satellite
    Select a Method From Standard Object Database
  2. Click the Insert button.
  3. Enter 29524 as the ID Number.
  4. Click Search.
  5. Select the DMSP 5D-3 F17D satellite with Source = Local Database.
  6. Click Insert.
  7. Close the Satellite Database tool.
  8. Close the Insert STK Objects tool.

Configure the Magnetic Field Model

Decide which field model(s) to use. The IGRF main-field with the Olson-Pfitzer external field gives the highest accuracy. Fast-IGRF is reasonably accurate alternative to the IGRF (within 1%) which offers some improvement in speed. The centered-dipole model is a good choice when computational speed is a high priority. Analysis under about 15000 km altitude generally do not require the external field model.

Choose the IGRF update rate. The harmonic coefficients of the IGRF main-field change slowly with time and are maintained in tables having nodal values added every five years typically. Between these nodes, the coefficients are linearly interpolated. The “update rate” determines how frequently the IGRF model coefficients are re-interpolated from the table. The default of one (1) day should be fine for most circumstances, but increasing this value to up to 30 days for very long orbits can improve computational speed.

  1. Open the satellite's () properties ().
  2. Select the Basic - SEET Environment page.

Since you are in a LEO orbit you will be considering a relatively short time period. You can just leave the default options.

Configure and Display the 3D Vector

  1. Bring the satellite's () properties () to the front.
  2. Select the 3D Graphics - Vector page.
  3. Enable the Nadir(Centric) vector.
  4. Disable the Show Label option.
  5. Enable the Velocity vector.
  6. Disable the Show Label option.

Add a Vector to the List

  1. Click the Add... button to bring the Add Vector Components button to the front.
  2. Locate the SEET_GeomagneticField vector and add it to the Name list.
  3. Click OK.

Display the New Vector

  1. Ensure the Show option is selected for the SEET_GeomagneticField is selected.
  2. Change the color of the vector.
  3. Disable the Show Label option.
  4. Enable the Show Magnitude option, if you'd like.
  5. Click Apply.

View the Vectors in 3D

  1. Select the satellite in the Object Browser.
  2. Zoom To the satellite in the 3D Graphics window.

    3. To observe the behavior of the geomagnetic field vector over time.

  3. Click the Play () button.
  4. Click the Reset () button.
  5. Save () the scenario.

Create a Report of Magnetic Vector Components

  1. Right-click the DMSP satellite and select Report & Graph Manager.
  2. Click the New Report Style button.
  3. Enter a name for the report like Magfield Vector.
  4. Expand the SEET Magnetic Field data provider.
  5. Move () the following items to the Report Contents field.
    • Time
    • B Field - ECF x
    • B Field - ECF y
    • B Field - ECF z
  6. Click OK.
  7. Generate the custom report.

Configure and Perform Magnetic Conjugacy Study

  1. Insert a Place () using the City Database () method. Select Boston, MA.
  2. Open Boston's () properties ().
  3. Select the Constraints - Basic page.
  4. Disable the Line of Sight option.
  5. Click Apply.

Set the DMSP Satellite Properties

  1. Open DMSP's () properties ().
  2. Select the Constraints - Basic page.
  3. Disable the Line of Sight option.
  4. Select the 2D Graphics - SEET Environment page.
  5. In the Magnetic Field Contour Line section, enable the Show 3D and Show L-shell value label options.
  6. Click Apply.
  7. Select the Constraints - SEET page.
  8. Enable the Min and Max options in the Magnetic Field Line Separation option.
  9. Set the Min Magnetic Field Line Separation to zero (0) deg.
  10. Set the Max Magnetic Field Line Separation to ten (10) deg.
  11. Click OK.

Generate Access Between DMSP and Boston

  1. Right-click DMSP () in the Object Browser.
  2. Select Access ().
  3. Select Boston in the Associated Objects field.
  4. Click Compute.

Generate an Access Intervals by Constraint Report

  1. Open the Report & Graph Manager ().
  2. Select Access as the Object Type.
  3. Expand () the Installed Styles directory.
  4. Generate the Access Intervals by Constraint report.

Generate a Geomagnetic Conjugacy Report

  1. Return to the Report & Graph Manager ().
  2. Change the Object Type to Satellite.
  3. Expand () the Installed Styles directory.
  4. Generate the SEET Geomagnetic Conjugacy report.
  5. Select Boston when the Available Objects dialog appears.
  6. Keep the Max Separation of 10 deg.
  7. Click OK.

View the Separation Angle in 3D

  1. Select the first time from the Geomagnetic Conjugacy report (e.g. approximately 1 Jul 2016 22:22:30.807).
  2. Paste that time into the epoch display for the 3D Graphics window.

    3. You should see something similar to this in your 3D Graphics window.