Elliptic orbits and satellite constellations for coverage of illuminated areas

Abstract

Synthesis of systems of continuous or periodic cov� erage of the Earth (from global coverage to survey of separate regions) is a traditional approach to the design of satellite constellations (SC). Following this line of research, the methods of ballistic design have been developed for various types of orbits and forms of coverage (1-7). A brief historical overview of develop� ment and modern state of the art of the theory of SC for continuous coverage is presented in (8). The SC in elliptic orbits of the Molniya type (9-11) form a spe� cial class. These orbits are characterized by the use of critical orbit inclination (i = 63.4° or i = 116.6°) and by position of the orbit apogee in the hemisphere including a coverage region. In this class socalled oneroute (or onepath) systems were developed (10) whose paths on the ground surface coincide (i.e., parameters of the orbits and Greenwich longitudes of their ascending nodes are identical). For the systems designed for surveying the Earth's surface and connected with illumination of observed regions by the Sun one can use SC of continuous cov� erage in highly elliptical orbits (11). However, this approach can be nonoptimal as far as the number of required satellites is concerned. The use of SC of peri� odic coverage, as a rule, cannot solve this problem, since arising gaps in survey have cyclic character and are not connected with illumination by the Sun. The goal of this work is to develop the methods of choosing economical SC designed for observation of illumi� nated regions and based on a new type of highly elliptic orbits of Molniya type. The latter are synchronized with the solar day, as opposed to the classical Molniya orbits that are synchronized with the Earth's rotation (i.e., with the sidereal day). It is worthy of noting that such orbits can also be used for the inverse problem: to survey some areas during nighttime (for example, for their illumination). Another possible application is satellite communication systems in which the intervals of visibility, determining the possibility of communi� cation, are connected to the local time with maximum communication traffic. PseudoSunSynchronous Orbits of the Molniya Type. Let us consider a certain region of observation. Let the region center have geographic longitude λН and corresponding local time scale tm. We assume that there is a certain highly elliptical orbit with the orbit period multiple to the solar day duration