Radiation Environment with SEET

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.

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)
  • Analysis Workbench
  • Coverage

Problem Statement

You are trying to determine if the orbit you have designed for your satellite will incur too much radiation. For the given space vehicle configuration, determine the following:

  • a low resolution data-based dose-depth curve for a long time base-line orbit (6 months)
  • a high resolution model-based dose-depth curve for a long time base-line orbit (6 months) using flux integration
  • a min/max flux comparison on an intermediate time base-line orbit (single day).

Break It Down

The primary decisions to make when developing a Radiation Environment scenario using STK involve determining which models to use and balancing accuracy or resolution of results versus computational speed.

  • Use an accurate and fast magnetic field model in your analysis such as IGRF Olson-Pfitzer.
  • Set the IGRF update rate to one (1) day.
  • Use the Radiation-Only Radiation Environment Model with a leo sec Dose Integration step.

The Radiation Environment component of STK's Space Environment and Effects Tool (SEET) capability provides a suite of models for computing energetic particle fluxes and fluences in near-Earth space, as well as ionizing dose rates and integrated doses behind shielding thicknesses you define (dose-depth curves.) The flux models provided include the Air Force Research Laboratory (AFRL) CRRES models as well as the standard NASA AE8/AP8 models for both protons and electrons. For dose quantities, the data based APEXRAD and CRRESRAD models are provided, which give total dose only for a limited set of shielding thicknesses, as well as the standard SHIELDOSE 2 model, which is highly configurable in terms of, for example, shielding thickness and detector type, and can provide the dosing due to protons, electrons and bremsstrahlung separately. Starting with SEET 9.2.3, computation with SHEILDOSE 2 has been sped up significantly by allowing you to select a “Dose Integration Step” and “Dose Report Step”. With these parameters, fluxes are accumulated at the time-resolution specified by the Dose Integration Step for a period corresponding to the Dose Report Step, and then passed to SHIELDOSE 2 for dose computation. Speed-ups are on the order of Dose Report Step over orbit time-step, e.g., 1440 min/1 min = 1440 for an integration interval of 1 day and orbit time step of 1 minute (assuming Dose Integration Step = orbit time step, which is a reasonable choice.) Note, to obtain the previous behavior of the model, simply set both the Dose Integration Step and Dose Report Step equal to the scenario time step.

Since the models for this component are essentially climatological databases obtained by binning satellite data in a magnetic coordinate space (specifically, LM and B/B0), a particular magnetic field model must be specified in order to access the data. Here, LM is the McIlwain L parameter, a mathematical way of indexing an energetic particle's drift shell, and B/B0 is the ratio of the local magnetic field to the minimum magnetic field along the field-line passing through the local point in space. LM and B/B0 are computed internally from the magnetic field model you specify (see the STK / SEET Magnetic Field Tutorial and the SEET user manual for more information).

Starting with SEET 9.2.3, two additional options for setting the magnetic field have been added to the SEET Radiation tab (in the Satellite Basic Properties list) which provide additional compatibility with the SPENVIS radiation environment computation technique. These options are “Set magnetic field epoch to Mode’s reference epoch” and “Shift SAA using Mode’s reference epoch”. Note that when these settings are selected, the magnetic field model selections set in the Satellite Basic SEET Environment tab are ignored for the purposes of radiation environment computations

Solution

Build a scenario that will cover the desired time period for the satellite orbit 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 low and high resolution dose-depth curves and a min/max flux comparison.

Video Guidance

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

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 ().
  2. Rename the Scenario SEET_RadiationEnvironment.
  3. For the analysis period, enter 1 Jul 2016 16:00:00.000 UTCG to 2 Jul 2016 16:00:00.000 UTCG. Click OK and save the new scenario.

Add a Satellite

Add a satellite () to the scenario. We will use a nominal eccentric orbit that covers a large portion of the inner belt and a smaller portion of the outer belt, which will exercise the Radiation Environment models in the desired manner.

    Option Value
    Select an Object to be Inserted: Satellite
    Select a Method Orbit Wizard
  1. In the Orbit Wizard window, set the Type to Orbit Designer, then fill in the following values:
    2. Option Value
    Semimajor Axis 15000 km
    Eccentricity 0.4
    Inclination 30 deg
    Argument of Perigee 50 deg
    RAAN 90 deg
    True Anomaly 0 deg
  2. Click OK.
  3. Close the Insert STK Objects window.

Change the Units

  1. Right-click the scenario object in the Object Browser and select Properties ().
  2. Select the Basic - Units page.
  3. Set the RadiationShieldThickness to Millimeters (mm).
  4. Select the Basic - SEET Radiation page.
  5. Set the NASA Electron and Proton Activity option to Solar Max.
  6. Click OK.

Configure the Magnetic Field model for use with the Radiation Environment models

This determines how frequently the IGRF model coefficients are recomputed. The default of 1 day should be fine for most circumstances, but increasing it to up to 30 days for very long orbits can improve computational speed.

Low-Earth Orbits (LEO) under about 1500 km altitude generally do not require the external field model. Tilted-dipole is a good choice when computational speed is a high priority. IGRF main-field with Olson-Pfitzer gives the highest accuracy. Fast-IGRF is reasonably accurate (within 1% of IGRF) and intermediate in speed. Fast-IGRF with Olson-Pfitzer external is typically a good choice here in nearly all circumstances.

  1. Right-click on the satellite object () in the Object Browser and select Properties.
  2. Select the Basic - SEET Environment page. You need to set the Magnetic Field parameters to use the Radiation Environment.
  3. Set the Main Field to Fast IGRF.
  4. Set the External Field to Olson-Pfitzer.
  5. Leave the IGRF update rate, 1 day.
  6. Click Apply.

Configure the Radiation Environment for a Long Time Base Dose-Depth Analysis

APEXRAD, CRRESRAD or Radiation-only (APEXRAD except where out of range of that model, in which case CRRESRAD is used) are fast, data based models but with a limited range of shielding depths. They should be used for computationally fast high resolution dose rate computation over long orbits. However, for access to the full range of SHIELDOSE 2 options (selectable depths, different detector types, species-resolved doses, greater spatial range of validity), either the CRRES or NASA models must be selected. The NASA models cover the broadest spatial and energy ranges while the CRRES models are based on more recent data (1990s.) When used in conjunction with large Dose Report Step sizes, these models can also provide computationally efficient high depth-resolution total dose-depth curves.

Next we will configure the Radiation Environment for a long time base-line dose depth analysis and generate the corresponding report. Since these generally take very long to compute, we will use the data-based models.

  1. Select the Basic - SEET Radiation page on the Satellite Properties.
  2. Ensure the Computational Model is set to Radiation Only.
  3. Ensure the Dose Channel is set to Total.
  4. Set the Dose Integration Step and Dose Report Step to 60 seconds.
  5. Disable the Set magnetic field epoch to Mode's reference epoch option.
  6. Click Apply.

Leave all other options at their default values, including the Shielding Thickness listed at the right.

In Radiation Only, CRRESRAD and APEXRAD Computational Modes, only the prescribed sets of shielding thickness may be used.

Create a Report

  1. Open the Report & Graph Manager ().
  2. Set the Object Type to Satellite.
  3. Expand the Installed Styles directory.
  4. Select the SEET Radiation Dose Depth report.
  5. Generate the report.

The report may not generate instantly.

Change the Units

The units of the shielding thickness can be changed.

  1. Right-click on Mils in the report to expose an option menu.
  2. Expand the Shielding thickness menu.
  3. Select the Units option.
  4. Disable the Use Defaults option.
  5. Set the New Unit Value to Millimeters (mm).
  6. Click OK.

Configure the Radiation Environment for a High Resolution Dose-Depth Analysis

Now you will configure the Radiation Environment for a high resolution (i.e. many depths) dose depth analysis and generate the corresponding report.

  1. Bring the satellite () properties () to the front.
  2. Select the Basic - SEET Radiation page.
  3. Set the Computational Mode to CRRES.
  4. Set the Detector Geometry to Spherical.
  5. Leave the other defaults.

Set the Shielding Thickness

  1. Click the Remove All button beside the Shielding Thickness option.
  2. Click the Add button.
  3. Enter one (1) mm in the text box that appears.
  4. Click the Enter key on your keyboard.
  5. Repeat those steps for the following set of shielding thickness:
    • Two (2) mm
    • Three (3) mm
    • Four (4) mm
    • Six (6) mm
    • Eight (8) mm
    • Ten (10) mm
    • Fifteen (15) mm

Create a Custom Report

  1. Bring the Report & Graph Manager to the front.
  2. Right-click on SEET Radiation Dose Depth report and select Properties.
  3. Select Section 1 in the Report Contents area.
  4. Click Remove.
  5. Expand the SEET Radiation Dose Depth on the left.
  6. Move () the following contents to the right.
    • Shielding Thickness
    • Electron Dose
    • Electron Brehsstrahlung Dose
    • Proton Dose
    • Combined Dose

Change the Units

  1. Select Shielding Thickness in the Report Contents area.
  2. Click the Units button.
  3. Disable the Use Defaults option.
  4. Click on a New Unit Value of Millimeters (mm).
  5. Click OK.
  6. Click OK on the Properties page.

    7. A warning is displayed asking to save this style under the My Styles directory.

  7. Click OK.

    8. A SEET Radiation Dose Depth report icon should now be selected under the My Styles directory.

  8. Generate the new report.

    9. This report could take a couple of minutes to generate depending on computer performance.

Generate a Radiation Electron Flux Graph

  1. Bring the Report & Graph Manager to the front.
  2. In the Time Properties box, Select Specify Time Properties
  3. Set the Stop Time to 2 Jul 2016 12:00:00.00 UTCG.
  4. In the Installed Styles directory, double-click on SEET Radiation Electron Flux graph.

Generate a Radiation Electron Flux Graph

  1. Open the satellite () properties ().
  2. Select the Basic - SEET Radiation page.
  3. Set the Computation Mode to NASA.
  4. Click Apply.
  5. Bring the Report & Graph Manager to the front.
  6. Generate the SEET Radiation Electron Flux graph.

    7. Do you notice the differences in scales and ranges of validity between the two graphs?

Displaying Radiation Belts with Volumetrics

  1. Right-click on the Satellite object and open Analysis Workbench.
  2. In the Analysis Workbench, select the Spatial Analysis tab.
  3. Create a new Spatial Calculation ().
  4. Set the following options:
    5. Option Value
    Type SEET Electron/Proton Radiation At Location
    Name Electron_0.65
    Flux Type Electron
    Particle Energy Electron Flux (0.650 MeV)

Create a New Volume Grid

  1. Change the Filter by option to All Objects
  2. Highlight the Earth object
  3. Create a new Volume Grid ().
  4. Set the following options for the Volume Grid:
    5. Option Value
    Type Carthographic
    Name Grid_1000kmTo50000km
    Parent CentralBody/Earth
  5. Set the Central Body to Earth
  6. Click the Set Grid Values... button.
  7. Set the following Grid Values for the Latitude:
    8. Option Value
    Latitude Fixed Number of Steps
    Minimum -60 deg
    Maximum 60 deg
    Number of Steps 60
  8. Set the following Grid Values for Longitude:
    9. Option Value
    Longitude Fixed Number of Steps
    Minimum 0 deg
    Maximum 180 deg
    Number of Steps 18
  9. Set the following Grid Values for Altitude:
    10. Option Value
    Altitude Fixed Number of Steps
    Minimum 1000 km
    Maximum 50000 km
    Number of Steps 50
  10. Click OK to accept the Grid Values.
  11. Click OK on the Add a Spatial Analysis Component window.
  12. Close Analysis Workbench.

Create a Volumetric Object

  1. From the Insert menu, go to Default Object and insert a Volumetric object.
  2. Open the Properties () of the new volumetric () object.
  3. Select the Basic - Definition page.
  4. Click the ellipsis () button beside the Volume Grid.
  5. Select the Filter by All Objects option in the Select Volume Grid window.
  6. Select Earth on the left.
  7. Select Grid_1000kmTo50000km in the My Components field.
  8. Click OK.
  9. Enable the Spatial Calculation and click on the ellipsis () button to select the spatial calculation.
  10. In the Select spatial calculation window, Filter by All STK Objects and select the satellite on the left.
  11. Select Electron_0.65 under My components on the right.
  12. Click OK.
  13. Click Apply.

Compute Volumetric

  1. Right-click on the Volumetric () object and extend the Volumetric menu to select Compute.
  2. Bring the Volumetric () object properties () to the front.
  3. Select the 3D Graphics - Attributes page.
  4. Enable the Smoothing option.
  5. Select the 3D Graphics - Grid page.
  6. Disable the Show Grid option.
  7. Select the 3D Graphics - Volume page.
  8. Enable the Spatial Calculation Levels option.
  9. Ensure the Show Fill Levels is enabled.
  10. Click Insert Evenly Spaced Values.
  11. Set the following values:
    12. Option Value
    Start 1.25e10
    Stop 2.25e11
    Step Size 1.25e10
    Start Color Red
    Stop Color Blue
  12. Click the Create Values button.
  13. Click Apply and bring the 3D Graphics window to the front.