Radiation Environment GCR and SEP

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)

Introduction to the Galactic Cosmic Ray (GCR) and Solar Energetic Particle (SEP) component

STK's Space Environment and Effects Tool (SEET) capability provides additional components for studying the radiation environment affecting a satellite. You will examine those here.

The SEET GCR component provides a suite of models for computing Galactic Cosmic Ray (GCR) fluxes and fluences near Earth. The models provided include CREME86, ISO-15390, and Badhwar-O’Neill 2010 (referred to as BO10). The primary differences among the models are the amount of data on which the model is based and the way they model the solar modulation. All three models calculate particle fluxes in free space outside the Earth’s magnetosphere; no geomagnetic cutoff effects are currently applied. Therefore, SEET output for GCRs currently consists only of reports and graphs and no 2D or 3D graphics. In addition, the model outputs are strictly applicable mainly to geo-synchronous altitudes and above. See the SEET User Manual for further information.

The SEET SEP component provides a suite of models for computing cumulative solar energetic particle fluences near Earth. The models provided include JPL-91, Rosenqvist, and ESP. Rosenqvist is essentially an update of JPL-91; ESP uses a different modeling approach and is based on a somewhat different data set. All three models calculate the probability of exceeding a given fluence above a given threshold energy in free space outside the Earth’s magnetosphere; no geomagnetic cutoff effects are currently applied. Therefore, SEET output for SEPs currently consists only of reports and graphs and no 2D or 3D graphics. In addition, the model outputs are strictly applicable mainly to geosynchronous altitudes and above; the output represents a maximal estimate for other orbits. See the SEET User Manual for further information.

Problem Statement

For a Geosynchronous satellite, determine the differential flux spectrum for Iron at solar minimum and solar maximum, as well as the probability of exceeding a given fluence.

Break It Down

The primary decisions to make when developing a GCR or SEP scenario using STK involve determining which models to use and the solar modulation conditions. For a GCR scenario, the BO10 model is based on the most recent and complete data sets; in this model you must currently select the solar modulation conditions. ISO-15390 is an international standard and calculates the solar modulation based on the STK scenario time. The CREME86 model is included mainly for historical purposes. In general, if GCR fluxes are needed over a long time period (more than about 2 years), the ISO-15390 model should be used since it calculates the solar modulation over time. If fluxes are required only at solar extrema or at an intermediate point, either ISO-15390 or BO10 can be used.

For an SEP scenario, you will use the ESP model. Inputs for JPL-91 and Rosenqvist are essentially identical; they only differ in the list of threshold energies available.

Solution

You will examine a few satellites/models: one which uses the ISO-15390 model to compute energy spectra every 0.5 years for a solar cycle, and one which uses BO10 to compute fluxes at solar minimum and the SEP environment for the ESP model.

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_GCR_SEP.
  3. Set the analysis period to the following:
    OptionValue
    Analysis Start Time22 Feb 1975 00:00:00.000 UTCG
    Analysis End Time22 Feb 1986 00:00:00.000 UTCG
  4. Click Ok.
  5. Open the scenario () properties ().
  6. Enable the Stop At Time option and ensure it is using the AnalysisStop Time.
  7. Set the Step Size to 300 seconds.
  8. Click OK.

Add a Satellite

You will use a nominal geosynchronous orbit since the GCR models apply here with no geomagnetic shielding.

  1. Insert a new satellite using the following method:
    2. Option Value
    Select an Object to be Inserted: Satellite
    Select a Method Orbit Wizard
  2. Set the following options:
    3. Option Value
    Type Geosynchronous
    Satellite Name GEO1
    Subsatellite Point -120 degrees
    Inclination 0 degrees
  3. Click OK.
  4. Close the Insert STK Objects tool.

Configure the GCR Environment to use the ISO-15390 Model for Iron Ions

Next you will configure the SEET GCR environment for the ISO-15390 model.

  1. Open GEO1's () properties ().
  2. Select the Basic - SEET GCR page.
  3. Select ISO 15390 as the Model type.
  4. Set the Atomic Number to 26 for Iron.

    5. The Solar influence box is grayed out since the model will use built-in parameters to compute it. The Interplanetary Weather Index and PHI will also be grayed out.

  5. Enter 0.5 Fractional Years as the Sample Time.
  6. Click OK.

Create a Report to List the Iron Differential Flux Spectra Over Time

  1. Open the Report & Graph Manager ().
  2. Ensure the Object Type is set to Satellite.
  3. Click Create New Report Style ().
  4. Give the new report a unique name like GCR Differential Flux and press Enter.
  5. Locate the SEET GCR Model in the Data Providers and move it to the Report Contents.
  6. Move () SEET GCR Differential Flux by Energy to the Report Contents.
  7. Click OK.

Generate the GCR Differential Flux Report

  1. Select GCR Differential Flux in the MyStyles directory.
  2. Click Generate.

In the definition section you will see the GCR model, atomic number, and other parameters.

A number of sub-sections for each time point in the analysis interval listing Particle Energy, Differential Flux, logarithm of particle energy, and log of differential flux for a range of energies.

Configure the GCR Environment to use the Badhwar-O'Neill model for Iron Ions at an Intermediate Period

Next you will configure the SEET GCR environment for the BO10 model.

  1. Bring GEO1's () properties () to the front.
  2. Select the Basic - SEET GCR page.
  3. Select BO10 as the Model.
  4. Set the Atomic Number to 26.
  5. Set the Solar Influence to Solar Max.
  6. Click OK.

The Interplanetary Weather Index and PHI are grayed out. The sample time shows whatever the last sample time set was, but it is grayed out and ignored for this scenario.

Create a Report to list the Iron Integral Flux Spectra

  1. Open the Report & Graph Manager ().
  2. Ensure the Object Type is set to Satellite.
  3. Click Create New Report Style ().
  4. Give the new report a unique name like GCR Integral Flux and press Enter.
  5. Locate the SEET GCR Model in the Data Providers.
  6. Move () SEET GCR Model Definition to the Report Contents field.
  7. Move () SEET GCR Integral Flux by Energy to the Report Contents field.
  8. Click OK.

Create a Graph of Integral Flux as a Function of Energy

  1. Open the Report & Graph Manager ().
  2. Ensure the Object Type is set to Satellite.
  3. Click Create New Graph Style ().
  4. Give the new graph a unique name and press Enter.
  5. Select XY as the Graph Type.
  6. Expand the SEET GCR Integral Flux by Energy data provider.
  7. Move () the Log(Particle Energy Level)to the X-Axis.
  8. Move () the Log(Integral Flux) to the Y-Axis.
  9. Click OK.
  10. Generate the new graph.

    11. The Reports and Graphs above are all available as default styles in the standard STK install with the following names: SEET GCR Differential Flux, SEET GCR Integral Flux, and SEET GCR Log Integral Flux vs Log Energy Level.

  11. Disable the satellite in the Object Browser to hide it from the Graphics windows.

Explore the SEP Scenario

Next you will explore the SEP scenario environment for the ESP model.

Create a New Satellite

  1. Insert a new satellite using the following method:
    2. Option Value
    Select an Object to be Inserted: Satellite
    Select a Method Orbit Wizard
  2. Set the following options:
    3. Option Value
    Type Geosynchronous
    Satellite Name GEO2
    Subsatellite Point -120 degrees
    Inclination 0 degrees
  3. Click OK.
  4. Close the Insert STK Objects tool.

Configure the SEP Environment to use the ESP Model

  1. Open GEO2's () properties ().
  2. Select the Basic - SEET SEP page.
  3. Select ESP as the Model type.

    4. The default list of energies is given in MeV. The Remove button can be used to restrict the list to just those energies. While the Reset to Defaults restores the original list.

  4. Click OK.

Create a Report to List the Probability of Exceeding a Given Influence as a Function of Threshold Energy

  1. Open the Report & Graph Manager ().
  2. Ensure the Object Type is set to Satellite.
  3. Click Create New Report Style ().
  4. Give the new report a unique name like SEP Fluence and press Enter.
  5. Locate the SEET SEP Model in the Data Providers.
  6. Move () the following options to the Report Contents field:
    • SEET SEP Model Definition
    • SEET SEP Fluence by Probability per Energy
      • Log(Probability)
      • Log(Fluence)
  7. Click OK.
  8. Generate the SEP Fluence report.

The report contains a definition section that gives the SEP model and the threshold energies. It also contains a number of sub-sections for energy listing the Fluence and Probability.

Create a Report

  1. Open the Report & Graph Manager ().
  2. Ensure the Object Type is set to Satellite.
  3. Click Create New Report Style ().
  4. Give the new report a unique name.
  5. Locate the SEET SEP Energy by Fluence in the Data Providers.
  6. Move () the following options to the Report Contents field:
    • Energy
    • Fluence
  7. Click OK.
  8. Generate the Report.

The reports and graphs are all available as default styles in the standard STK install with the following names: SEET SEP Fluence by Probability per Energy and SEET SEP Fluence by Energy per Probability to Exceed.