COVERAGE TIME VARIATION IN A NEAR-EARTH DATA RELAY SATELLITE SYSTEM

摘要

The objectives of this paper are to understand the coverage time variation for a data relay satellite system (DRSS) due to different circular low-Earth orbits (LEO) defined by inclination and right-ascension of the ascending node (RAAN). It is of importance to understand this variation when designing a communications system for tele-presence (TP) in order to achieve real-time Earth observation or to use TP operations to enable on-orbit servicing (OOS) using robots in space. In order to analyze the coverage time variation for a DRSS an orbit analysis model has been developed and implemented in MATLAB to simulate all possible circular orbits around Earth. The coverage time variation for a 500 km circular orbit is presented as well as the results for a 1000 km orbit. A comparison of the results for these two orbit altitudes shows a decrease in mean coverage time during one day from 62-80 min for a 1000 km orbit to 50-65 min for a 500 km orbit. The upper value for the coverage time is for orbits with an inclination around 90° and it decreases for lower inclined orbits. The analysis shows that there are certain revolutions in orbits with inclination close to 90°that will never experience any eclipses in the DRSS and these are the time slots to be used when optimizing the system to coverage time.