STK / SEET MAGNETIC FIELD TUTORIAL
Contents
INTRODUCTION ......................................................................................................... 1
PROBLEM STATEMENT................................................................................................. 1
GETTING STARTED ..................................................................................................... 2
SOLUTION APPROACH ................................................................................................. 2
Create the Scenario ......................................................................................... 2
Configure the Magnetic Field Model .................................................................... 3
Configure the Display 3D Vector ........................................................................ 3
Create a report giving the magnetic vector components ....................................... 5
Configure and perform magnetic conjugacy study ............................................... 5
RESULTS AND ANALYSES ............................................................................................ 7
Licenses Needed
This tutorial requires that you be licensed for the STK Space Environmental Effects Tool (SEET).
Introduction
The 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 fieldlines (such as the patterns produced in iron filings by a bar magnetic). The field-lines 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.
Problem Statement
For a given space-vehicle configuration and orbit, and for a specified ground station, determine the local magnetic vector location along the orbit and the times when the spacecraft location is magnetically conjugate to the ground station.
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Getting Started
The primary decisions to make before developing a Magnetic Field model scenario using
STK involve balancing model accuracy versus computational speed:
• 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. Analyses 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.
Solution Approach
Build a scenario that will cover the desired time period for the satellite orbit of interest.
Add a ground station of interest. Set the relevant model parameters to achieve the desired
balance between accuracy and computational speed. Configure STK properties as needed
to obtain the desired display.
Create the Scenario
1. Create a new scenario by using the New Scenario Wizard, by selecting “New…”
from the File menu, or by clicking the corresponding toolbar button . Fill in the
scenario name and description as desired. For the analysis period, enter 14 Oct
2009 16:00:00.000 UTCG to 15 Oct 2009 16:00:00.000 UTCG. Hit OK.
2. Next, add a satellite to the scenario that will exercise the Magnetic Field model in
the desired manner. This tutorial will use an existing DMSP satellite. This satellite
transits a sun synchronous orbit at around 850km altitude.
If the Insert New Object Tool dialog box is not already visible, select “New…”
from the Insert menu. In the “Insert STK Objects” dialog box, select Satellite under Scenario Objects and “From Standard Object Database” under Select a Method and hit Insert. Select the Local tab. In the SSC Number edit box, enter 29524
and hit the Search button. A single satellite named “DMSP 5D-3 F17 D” should
appear in the list. Select it and hit Insert. Close the Insert Satellite from Database
dialog box.
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3. Close the Insert STK Objects panel. Save the scenario.
Configure the Magnetic Field Model
4. Display satellite properties for modification by right-clicking on the satellite object in the Object Browser panel and select “Properties…”. In the properties panel
tree, under Basic, select “SEET Environment”. The upper dialog box contains the
magnetic field parameters. Since we are in a LEO orbit and will be considering a
relatively short time period, we will use the default selections: IGRF main-field,
no external field, and 1 day IGRF update rate.
Configure the Display 3D Vector
5. Within the satellite properties under 3D Graphics, select Vector. In the vector list,
select the Show checkbox for Nadir(Centric) Vector. De-select the “Show Label”
option.
6. In the vector list, select the Show checkbox for Velocity Vector. De-select the
“Show Label” option.
7. Click the Add… button to bring up the “Add Vector Components” dialog. Under
the satellite object, select the SEET_GeomagneticField vector and add it to the selected Name list. Hit “OK”.
8. Back in the 3D Graphics Vector panel, ensure that the Show checkbox for the
SEET_GeomagneticField is selected. Change the color and de-select “Show Label” option. Select “Show Magnitude” if desired. Click the “Apply” button to apply changes.
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9. To view the vectors selected in the previous step, right-click on the satellite object
and select Zoom To, and then bring forward the 3D Graphics window if necessary.
10. To observe the behavior of the geomagnetic field vector over time, select the Play
button
from the Animation toolbar. Press the Reset button
when finished.
Save the scenario.
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Create a report giving the magnetic vector components
11. In the Object Browser, right-click on the DMSP satellite and select Report &
Graph Manager.
12. In the Report and Graph Manager dialog box, right-click on My Styles. Select
New and then Report. Enter a name for the report (e.g., Magfield Vector) and hit
Enter.
13. In the Report Style dialog box, scroll through the Data Providers list to the “SEET
Magnetic Field” set and expand the set by clicking the plus symbol . Move
“Time”, “B Field – ECF x”, “B Field – ECF y”, and “B Field – ECF z” to the Report Contents list by highlighting them and clicking the arrow button . Hit OK
to close the panel.
14. Returning to the Report and Graph Manager dialog, select “Generate…”. A report
window will be displayed containing the data selected for the report.
Configure and perform magnetic conjugacy study
15. Insert a ground facility (here “Boston”). From the main menu, select Insert ->
From Standard Object Database -> City…. Type in Boston in the City Name box
and click Search. Highlight Boston, Massachusetts, Insert and Close.
16. In the Object Browser, right click on the Boston facility object and select “Properties”. Under “Constraints”, select “Basic” and de-select the option labeled “Line-
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of-sight”, then click Apply.
17. Go to the DMSP satellite properties page. Under “Constraints”, select “Basic” and
de-select the option labeled “Line-of-sight”, and then click Apply.
18. Staying on the DMSP satellite properties page, under “2D Graphics”, select
“SEET Environment”. Within the Magnetic Field Line Contour pane, select
“Show 3D” and “Show L-shell value label”, and then click Apply.
19. Staying on the DMSP satellite properties page, under “Constraints” select
“SEET”. In the “Magnetic Field Line Separation” box, check the box by Min and
enter 0 deg; check the box by Max and enter 10 deg. Click OK.
20. In the Object Browser, right click on the DMSP satellite object and select Access
Tool. Click on “Boston” in the Associated Objects box, then click Compute.
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Results and Analyses
21. Produce an Access Report between the spacecraft and the facility by bringing up
the Report and Graph Manager page. For the “Object Type”, choose Access. Under “Installed Styles”, double-click on “Access Intervals by Constraint”.
22. Produce a Geomagnetic Conjugacy Report by returning to the Report and Graph
Manager page. For the “Object Type”, change to Satellite. Under “Installed
Styles”, double-click on “SEET Geomagnetic Conjugacy”. When the Available
Objects options box appears, make sure that Boston is highlighted and click OK.
23. Return to the 3D Graphics window and select the Play button from the Animation toolbar. Press the Reset button when finished. Save the scenario.
24. Choose a time from the Geomagnetic Conjugacy Report when the Separation angle is near minimum, e.g. 14 Oct 2009 21:37:00.000. Paste this value from the report and into the epoch display for the 3D Graphics window. Something similar to
the following screenshot should appear.
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