Designing Transfers to Geostationary Orbit Using Combined Chemical–Electric Propulsion

Although it is clear that electric propulsion can deliver more payload mass when compared to conventional chemical propulsion, near-term transfers to geostationary-equatorial orbit will likely use both propulsion modes in order to reduce the transfer time. Determining the best starting orbit for the subsequent electric-propulsion phase is the key to computing time-constrained maximum-payload transfers to geostationary orbit. Numerical optimization methods are used to determine the unique optimal starting orbit for a given low-thrust velocity increment to be performed by the electric-propulsion stage. This approach yields a purely analytical algorithm that can determine spacecraft mass requirements for a desired electric propulsion system and desired transfer time. Numerical examples are presented in order to demonstrate how this tool can be used to rapidly perform trade studies for transfers that use chemical and electric propulsion stages.