tion is influenced by the solar cycle through increased aerodynamic drag effects. Mitigation provisions for the micrometeoroid and orbit debris threat is to choose altitude and inclination orbit architecture with minimal presence of orbit debris, locate critical devices and structures away from the ram direction, and the use of a layered "bumper" structure to protect critical elements. Space Radiation Effects on Devices and Technologies The interaction of the environment described in the previous section with devices used in the implementation of systems results in long-term effects which produce degradation in performance and may potentially induce component failure over the mission life. Long-term mission integrated consequences include total ionizing dose and displacement damage dose effects on devices. Single event effects occur due to the traverse of a single energetic particle through sensitive device structures. Single event effects may impart or enable permanent changes and destructive damage to devices, or may result in non-destructive but transient effects which perturb normal device operation. Mission Integrated Effects 4.1.1 Total Ionizing Dose [Dressendorfer98] Total ionizing radiation effects result from the interaction of charged particles or photons having sufficient energy to break atomic bonds within device materials, creating electron-hole pairs via ionization. The amount of ionization is expressed as the total dose absorbed over the exposure (mission) in the device material, expressed in units of rad(SiO2) or other appropriate units of rad(material). Total ionizing dose effects predominantly occur in the material used in the operation of active devices (MOSFETs), and in oxides used to insulate, isolate, or guard active device structures. In MOS transistors, trapped charges and interface traps result in changes in threshold voltage, Vt. Magnitude of the threshold voltage shift has been shown to exhibit power law dependence on oxide thickness. Modern active device structures fabricated using gat