Extension of Highly Elliptical Earth Orbits Using Continuous Low-Thrust Propulsion

Abstract

Extension of highly elliptical orbits, with free selection of orbit period, using low-thrust propulsion is investigated. These newly proposed orbits, termed Taranis orbits, are enabled by existing low-thrust propulsion technology, offering a radically new set of tools for mission design and facilitating novel Earth Observation science. One example, using general and special perturbation techniques, is the application of continuous low-thrust to alter the "critical inclination" of an orbit from natural values of 63.4 or 116.6 deg, to any inclination required to optimally fulfil mission goals. Continuous acceleration is used to compensate for the drift in argument of perigee caused by Earth’s gravitational field. Pseudospectral optimization techniques are applied to the 90 deg inclination Taranis orbit, generating fuel-optimal control profiles, with a fuel saving of from general perturbation results. This orbit provides an alternative solution for high-latitude imaging from distances equivalent to geostationary orbits and enables continuous visibility of frigid and neighboring temperate regions using three spacecraft, enabling high-quality imaging prohibited using conventional orbits. Finally, order of magnitude mission lifetimes and a Strawman mass budget are developed, where mission lifetimes for spacecraft with initial mass of 1000, 1500, and 2500 kg are limited to 4.3, 6, and 7.4 years, respectively.