from satellite measurements between 1959 and 1978. The models are empirical data sets, and provide separate models for the solar minimum and solar maximum phases. The flux values represent long term average conditions over the entire interval of the indicated phase of the solar cycle. The extremities encountered at the peak (maximum or minimum) of the phase and short term variance in the particle flux is not represented. An uncertainty factor of two is considered applicable for these models, and short-term excursions from the model averages are indicated to possibly reach an order of magnitude. A number of issues have been identified regarding the use of these models, including the particle flux levels and spectra at low altitudes, secular variation of the geomagnetic field since release of the models, and the inability to represent the anisotropic characteristic of particle flux. Slow changes in geomagnetic field conditions result in the South Atlantic Anomaly (SAA) location presently residing approximately 6.5° west of the position indicated by the NASA models. This characteristic is of no importance in assessment of mission integrated dose; however, it can be of importance to missions which must assess system effectiveness and quality of service provided to users in this region, and in developing fault avoidance provisions for SAA traverses. Particularly for low altitude missions, understatement by the model of the trapped proton population by factors ranging from 1.55 to 2.30 have been indicated. Other modeling of anisotropy in the environment indicates the possibility of east-west ratios exhibiting factors between two and seven at low altitudes in the SAA region. This characteristic is important to the consideration of the benefits which shielding provide in the transport of particle spectra to the device or component level. The trapped electron model, AE8, has been shown to over-predict the inner belt region trapped electron flux; the error attributable to increased levels remaining from high altitude nucle