Comparative analysis of selected radiation effects in Medium Earth Orbits

Abstract

Satellite design is well developed for the common Low Earth Orbit (LEO) and Geosynchronous Orbit (GEO) and Highly Elliptical Orbits (HEO), i.e., Molniya, cases; Medium Earth Orbit (MEO) satellite design is a relatively new venture. MEO is roughly defined as being altitudes above LEO and below GEO. A primary concern, and a major reason for the delay in exploiting the MEO altitudes, has been the expected radiation environment and corresponding satellite degradation anticipated to occur at MEO altitudes. The presence of the Van Allen belts, a major source of radiation, along with the suitability of GEO and LEO orbits, has conventionally discouraged satellite placement in MEO. As conventional Earth orbits become increasingly crowded, MEO will become further populated. This thesis investigates the major sources of radiation (geomagnetically trapped particles, solar particle events and galactic cosmic radiation) with respect to specific Naval Research Laboratory (NRL) designated MEO (altitudes between 3,000 nautical miles (nmi) and 9,000 nmi; inclination angle of 15 degrees). The contribution of each of these components to the total radiation experienced in MEO and the effects of the expected radiation on a representative spacecraft are analyzed in comparison to a baseline LEO orbit of 400 nmi and 70 degrees inclination. Dose depth curves are calculated for several configurations, and show that weight gains from necessary expected shielding are not extreme. The radiation effects considered include proton displacement dose and solar cell degradation.