Thrust vector stability for an electrostatic ion engine can be measured with improved sensitivity and time resolution by the method described here. Four double‐wire Langmuir probes, aligned in the form of a cross, are placed in the exhaust plume and are translated by a motorized positioning system to balance the currents collected along two orthogonal axes. The thrust vector position is thereby measured with an angular resolution of <0.01° and a response time of <5 s. ©1994 American Institute of Physics.