The Inclination Window for Low Earth Sun Synchronized Satellite Orbits

Abstract

LEO (Low Earth Orbit) environmental satellites provide continuous coverage of Earth, supplying meteorological and oceanic observation data which are important in aerospace and maritime. The missions of such satellites are mainly based on photo imagery. For photo imagery, it is also important that the area observed from the satellite is treated under the same lighting conditions. This can be achieved by keeping the orbital plane position constant relative to the Sun due to the Earth’s motion around the Sun, defined as orbital Sun synchronization. The line of nodes defines the orientation of the satellite’s orbital plane in space. Nodal regression is defined as the shift of the orbit’s line of nodes over time, as Earth revolves around the Sun. Nodal regression is caused by the Earth’s oblateness. Nodal regression is a very useful feature, especially used to synchronize low Earth circular orbits with the Sun. Nodal regression depends on orbital attitude and orbital inclination angle. This paper provides an inclination window calculation for different attitudes in order to maintain orbital Sun synchronization.

Orbital Perigee Deviation under Inclination Window for Sun Synchronized Low Earth Orbits

“…2) [12]. Through these two parameters could be achieved Sun synchronization, deeply elaborated under [9]. Sun-synchronization is typical for LEO orbits, since for MEO and GEO orbits (too much higher radius) the nodal regression tends to be infinitesimal, thus MEOs and GEOs could not be Sun synchronized.…”

“…Since the nodal regression effect is typical for LEO orbits, under manuscript [9] it is elaborated the range of the inclination for different LEO orbit altitudes for Sun synchronization to be achieved. Considering Van Allen belt effect (above 1400km) [14], for simulation purposes are considered attitudes from 600km up to 1200km.…”

“…The Sun synchronization is achieved only when daily nodal regression (ΔΩ) is equal of 0.9856[º/day], represented with the straight line in the Fig. 3, identified with 0.986 above it [9]. For orbital altitude of 600km (the lowest altitude considered under simulation conditions) consequently stems 7000   r a km under no eccentricity ( 0  e ) will get inclination for sun synchronization as:…”

“…These are known also as "frozen" orbits, because the Sun synchronous orbit keeps constant geometry to the Sun representing an advantage for remote sensing process and the appropriate instruments. The mathematical background of the Sun synchronization process for low Earth orbits is based on terrestrial potential expression through zonal harmonics and it is presented by [9] where the methodology of inclination window determination for the Sun synchronization is also given. The following elaboration moves a step ahead by calculating the perigee deviation within an already determined inclination window for the Sun synchronized orbits.…”

“…The satellite's position in space is defined by space orbital parameters, what is too shortly described at second section. Further for the determined inclination window of the Sun synchronization under [9] it is calculated the orbital perigee deviation under different altitudes within the inclination window range.…”