STK/SEET Radiation

The STK/SEET Radiation Environment computes the expected dosage rate and accumulated dose (ionizing energy deposition) due to energetic electron and proton particle fluxes for a range of shielding thicknesses, and also computes the energetic proton and electron fluxes for a wide range of particle energies. The STK/SEET Radiation Environment incorporates the following models from Air Force Research Laboratory’s AF-GEOSpace program version 2.1P: APEXRAD, CRRESRAD, CRRESELE, CRRESPRO, NASAELE, and NASAPRO. For dose computations in combination with the CRRES or NASA flux models, the SHIELDOSE-2 radiation-transport model is used to estimate ionizing energy deposition (dose).

The CRRES proton and radiation database models (CRRESPRO and CRRESRAD) are categorized according to whether the data were collected before or after the large solar storm of March 24, 1991. Data collected after the storm is considered to be more active than data observed before the storm. Note that orbits with apogees near geosynchronous altitudes may show a higher dose rate using the average model than using the active or quiet models because the average model uses the period between 19 March 1991 and 31 March 1991 during which a strong solar proton event occurred (Kerns and Gussenhoven, 1992).

For additional background information, consult SEET: Space Environment and Effects Tool for STK (PDF).

Options for STK/SEET Radiation CRRES Activity

Option Description
Proton Options are:
  • Active - model based on data during higher solar activity reference obtained from 31 March 1991 to 12 October 1991 (after the large 24-Mar-1991 storm).
  • Quiet - model based on data during lower solar activity from 27 July 1990 to 19 March 1991 (before the large 24-Mar-1991 storm).
Radiation

Options are:

  • Active - model based on data during higher solar activity reference obtained from 31 March 1991 to 12 October 1991 (after the large 24-Mar-1991 storm).
  • Average - model based on the average of data taken over the entire CRRES mission.
  • Quiet - model based on data during lower solar activity from 27 July 1990 to 19 March 1991 (before the large 24-Mar-1991 storm).

Options for NASA Electron and Proton Activity

Option Description
Activity

Options are:

  • Solar Min - Sets values for the NASA models NASAELE and NASAPRO appropriate for the minimum of the solar cycle.
  • Solar Max - Sets values for the NASA models NASAELE and NASAPRO appropriate for the maximum of the solar cycle.

The CRRESELE database model returns electron flux at discrete energies in the range 0.5-6 MeV, reporting electron fluxes for a specific set of energy levels only (0.65, 0.95, 1.60, 2.00, 2.35, 2.75, 3.15, 3.75, 4.55, 5.75 MeV). Similarly, the CRRESPRO database model computes proton flux at discrete energies in the range 1-100 MeV, reporting proton fluxes only for a specific set of energy values only (1.5, 2.1, 2.5, 2.9, 3.6, 4.3, 5.7, 6.8, 8.5, 9.7, 10.7, 13.2, 16.9, 19.4, 26.3, 30.9, 36.3, 41.1, 47.0, 55.0, 65.7, 81.3 MeV).

The NASAELE electron-flux model computes electron flux using the NASA AE-8 radiation belt models at energies between 0.04 and 7.0 MeV, and the NASAPRO proton-flux model computes proton flux using the NASA AP-8 radiation belt models at energies between 0.1 and 400 MeV. Unlike the CRRESELE and CRRESPRO database models, the user may specify the energy levels for the NASA models.

Options for NASA Model Energy Levels

Option Description
NASA Energies

Options are:

  • Default -The default energy levels will be those from the CRRESS models.
  • Custom - Levels between 0.04 and 7.0 MeV may be specified for the NASA electron-flux model, and levels between 0.1 and 400 MeV for the NASA proton-flux model.

  • When using the NASA models, a minimum of three (3) electron energy levels are needed to compute electron and Bremsstrahlung dose and dose rates, and at least three (3) proton energies are needed to compute proton rates and doses.

References

AF-GEOSpace User’s Manual Version 2.1 and 2.1P, AFRL/RVBS, 29 Randolph Rd, Hanscom AFB, MA 01731 (2006).

Kearns, K.J. and M.S. Gussenhoven (1992), CRRESRAD Documentation, PL-TR-92-2201, Phillips Laboratory, Hanscom AFB, MA, ADA 256673.