Energy Range (MeV)





Log Fluence (cm-2)

8.27 ± 0.59

7.28 ±0.75

6.63 ± 0.95

5.77 ±124

Log Peak Flux (cm-2 sec"1) 3.27 ± 0.64

2.37 ±0.82

1.88 ±0.78

Figure 8-12 shows the probability of the proton fluence (energy >10 MeV) exceeding a given value over time intervals of 1-7 years (typical of the durations of many satellite missions). Solar array outputs typically degrade by a few percent following exposure to fluences above ~109 cm-2 at energies over -1 MeV, but actual degradation rates depend on cell type, cover glass thickness, and cell age.

Galactic Cosmic Rays*

Galactic cosmic rays, or GCR, arc particles which reach the vicinity of the Earth from outside the solar system. The number and type of nuclei in these particles are proportional to those in solar system material. Figure 8-13 shows the energy spectrum for several elements. The sum of the curves in the lower energy portion of the figure suggests that cosmic rays undergo solar-cycle modulation.

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