are heavily shielded, and the peak in the transported proton spectra is shifted to higher energies, typically between 40-100 MeV. (Refer to part IVA, section 2 for a description of proton environments and shielding.) For this reason, and because package penetration and energy deposition uniformity issues are simplified when very penetrating protons are used, higher energy protons are frequently employed for radiation tests. In this approach any error introduced by a lack of correlation between the measured property and the displacement damage function is minimized. The optimal choice for a single test energy is the one that best represents the damage-weighted proton spectrum calculated using a displacement damage function. As illustrated in the next section, one can calculate the differential or integral displacement damage energy deposition as a function of proton energy and use these results to aid in the selection of proton test energies [Dale91]. IV-68 Once one or more proton test energies have been chosen for a particular space mission, the relevant MeV-equivalent fluences can be calculated using the calculated NIEL (or an experimental damage function) and the differential proton fluence spectrum, dd(E)/dE, for the time period of interest. Note that a given mission may be represented by a time-weighted sum of more than one differential spectrum depending on the details of orbital precession, solar cycles, etc. The MeV-equivalent proton fluence at a given test energy, Etest is given by: where the numerator is just the total displacement damage dose in units of MeV/g when NIEL(E) is expressed in units of MeVcm2/g. The integration limits, E1 and E2, generally correspond to the lowest and highest proton energies provided in the differential spectrum, typically from about 0.01 MeV to about 500 MeV. Note that the range of integration may be reasonably adjusted depending on the degree of shielding present [Dale91, Mess97]. As an example, a 60 MeV-equivalent fluence is simply the fluence of 60 MeV protons that produ