Power system for electrical propulsion in space applications

Ion engines, also known as electrical propulsion, are used more and more in space applications due to its higher power density and its lower contamination risk than with chemical propulsion. One of its characteristics is that it needs a very stable power supply. This paper proposes a solution for the BepiColombo mission to Mercury. Electrical propulsion increases the electrical power demand of the spacecraft (in the range of 8 kW up to 14 kW for the BepiColombo Mission), generating new research opportunities on selecting the best Solar Array Regulator topology. Other missions now under study and looking for the future are Lunar Exploration. Solar electric propulsion (SEP) is used during the cruise period from Earth to Mercury in the BepiColombo mission. The Solar Array (SA) power increases with time and its associated propulsion unit has to take the maximum available power from the SA to use in the ion drive motor in order to reach Mercury within a reasonable time. Ion Thrust is not required in eclipse and therefore a Power System was designed that did not require a Battery and therefore a considerable mass could be saved. The paper describes a solution for the Mercury Transfer Module (MTM) Power Conditioning and Distribution Unit (PCDU) of the Solar Electric Propulsion Module (SEPM). The new conception is a Sequential Switching Shunt Maximum Power Regulator (S3MPR) consisting in a Sequential Switching Shunt Regulator (S3R), to keep the SA voltage at its Maximum Power Point (MPP) followed by a Boost regulator to produce a constant 100 V to supply the Electronic Propulsion (EP). A scaled-down Power Subsystem of 1 kW output power has been built and tested.