TRP: AP8MIN/MAX Trapped Proton Fluxes

Overview

Geomagnetically trapped protons are the primary cause of single event effects (SEEs) in many spacecraft systems deployed in low-Earth orbits. TRP provides omnidirectional trapped proton spectra appropriate for evaluating these SEE rates, based on the NASA AP8 models.

• TRP calculations are necessary only for orbits inside Earth's magnetosphere. They are not relevant to interplanetary orbits or to orbits beyond geosynchronous.
• TRP simultaneously calculates both orbit-averaged and peak trapped proton fluxes.
• IMPORTANT: Our TRP calculations have a limited range of applicability.
• IMPORTANT: The AP8 models are also known to have limited accuracy.

Inputs

To run TRP, you must:

1. Choose one of the available pre-calculated trapped proton spectra, OR, if pre-calculated proton spectra are not available for your orbit, specify your orbital parameters ;
2. Select AP8MIN (for missions near solar minimum) or AP8MAX (for missions near solar maximum).
3. Specify whether you want to calculate a single trapped proton spectrum, averaged over the whole orbit, OR do separate calculations for different orbital segments dilineated by McIlwain L. - The orbital segments option is not available if you have chosen the pre-calculated proton spectra. - In the orbital segments option, TRP can divide the orbit in up to 10 segments. Output files for these segments have names ending in ".tr#", where # = 1,2,3,4,5,6,7,8,9,X.
4. Specify a rootname for the output files. TRP will automatically create two output files, called "something_ave.trp" for the orbit-averaged trapped proton flux and "something_peak.trp" for the peak trapped proton flux in your orbit, where "something" is the rootname you have chosen. The program automatically adds the extensions "_ave.trp" and "_peak.trp" to the filenames.

You can use CREME's TRP routine to calculate omnidirectional trapped proton spectra for arbitrary orbits by specifying these orbital parameters:

• apogee (in either km or nautical miles)
• perigee (in the same units as apogee)
• orbital inclination (in degrees, measured from the equator)
• initial longitude of the ascending node (in degrees; suggested default = 0.)
• initial displacement from ascending node (in degrees; suggested default = 0.)
• displacement of perigee from ascending node (in degrees)

In addition, you must also specify the number of orbits.

Whenever possible, you should use the pre-calculated trapped spectra, since the TRP routine can require a great deal of CPU-time.

Outputs

Files produced by the TRP routine contain the differential trapped proton spectrum (in protons/m²-s-sr-MeV) vs. kinetic energy (in MeV) at the surface of the spacecraft, before transport through shielding.

Files created by the TRP routine have names of the form .tr.

• Files created using the whole orbit option end in the extension .trp
• Files created using the orbital segment option end in extensions .tr#, where "#" takes on values of 1,2,3,4,5,6,7,8,9,X for the various segments.

The TRP output files also contain header information which documents the inputs and parameters which produced it. You can examine this header information (to make sure, for example, that you've selected the .trp file you want).

TRP output files are written in a special format which suppresses the energy values. This format can be decoded into two-column tables, with energy (in MeV) in the first column and the differential trapped proton flux (in protons/m²-s-sr-MeV) in the second column. You can also download these two-column tables to your own PC for plotting with your own software. At the top of this table will be header information (with "%" in the second column of each header line). Note that you may have to delete some or all of these header lines before passing the file to your plotting software.

TRP output files can be used in several ways:

1. The .tr files can be used as input to the TRANS calculation, in order to account for degradation of the trapped proton flux in the satellite shielding.
2. The orbit-averaged trp file can also be input to the FLUX routine, to combine the trapped protons with non-trapped particles, such as Galactic cosmic rays. The FLUX output file can then input to the TRANS routine, as outlined above. This procedure is recommended for orbit-averaged calculations, in order to account for all sources of SEE-producing particles. Note that before running FLUX, you must also run GTRN to evaluate the orbit-averaged effects of geomagnetic shielding on the Galactic cosmic rays.

See also: Plotting CREME96 Spectra