Static highly elliptical orbits using hybrid low-thrust propulsion

Static, highly elliptical orbits enabled using hybrid solar-sail/solar-electric propulsion are investigated. These newly proposed orbits, termed Taranis orbits, have free selection of “critical inclination” and use low-thrust propulsion to compensate for the drift in argument of perigee caused by Earth’s gravitational field. In this paper, a 12 h Taranis orbit with an inclination of 90 deg is developed to illustrate the principle. The acceleration required to enable this novel orbit is made up partly by the acceleration produced by solar sails of various characteristic accelerations, and the remainder is supplied by the electric thruster. Order-of-magnitude mission lifetimes are determined, and a strawman mass budget is developed for two system constraints; first, spacecraft launch mass is fixed and, second, the maximum thrust of the thruster is constrained. Fixing maximum thrust increases mission lifetimes, and solar sails are considered near- to midterm technologies. However, fixing mass results in negligible increases in mission lifetimes for all hybrid cases considered, and solar sails also require significant development. This distinction highlights an important contribution to the field, illustrating that addition of a solar sail to an electric propulsion craft can have negligible benefit when mass is the primary system constraint. Technology requirements are also outlined, including sizing of solar arrays, propellant tanks, and solar sails.