Extension of the Molniya orbit using low-thrust propulsion

Extension of the standard Molniya orbit using low-thrust propulsion is presented. These newly proposed, highly elliptical orbits are enabled by existing low-thrust propulsion technology, enabling new Earth Observation science and offering a new set of tools for mission design. In applying continuous low-thrust propulsion to the conventional Molniya orbit the critical inclination may be altered from the natural value of 63.4deg, to any inclination required to optimally fulfill the mission goals. Analytical expressions, validated using numerical methods, reveal the possibility of enabling a Molniya orbit inclined at 90deg to the equator. Fuel optimal low-thrust control profiles are then generated by the application of pseudo spectral numerical optimization techniques to these so-called Polar-Molniya orbits. These orbits enable continuous, high elevation visibility of the Frigid and Neighboring Temperate regions, using only two spacecraft compared with six spacecraft required for coverage of the same area with a conventional Molniya orbit. This can be achieved using existing ion engines, meaning no development in technology is required to enable these new, novel orbits. Order of magnitude mission lifetimes for a range of mass fractions and specific impulses are also determined, and are found to range from 1.2 years to 9.4 years. Where, beyond 9.4 years the outline mass budget analysis for spacecraft of initial masses of 500kg, 1000kg and 2500kg, illustrated there is no longer a capacity for payload for all initial mass of spacecraft.