Minimum emission current of indium‐field emission electric propulsion thruster

PurposeField emission electric propulsion (FEEP) thruster is a type of electric propulsion based on space‐proven indium liquid metal ion sources. The lifetime of FEEP thruster limits its application in space. A better method to improve its lifetime is the reduction of emission current. This paper aims to discuss the minimum emission current of operating FEEP thrusters.Design/methodology/approachIn this work, theoretical models, including fluid‐flow model and ion formation model, are analyzed. Current densities of these models are discussed and the minimum emission current is calculated.FindingsThere are few equilibrium states under low emission current conditions. However, the minimum emission current is the only stable state at which the FEEP thruster can operate.Research limitations/implicationsThis analysis is mainly based on the needle indium FEEP, which is compared indirectly with experiments of gallium.Practical implicationsThis paper attempts to help designers choose appropriate electric parameters to improve the lifetime of FEEP.Originality/valueBy introducing and analyzing theoretical models, this paper calculates the minimum emission current for stable operation of FEEP.