A modified helium cooled ion source was operated in supersonic gas flows simulating some conditions of a rocket flight through the upper mesosphere and lower thermosphere. It is shown that the shock in front of this ion source is removed due to the low temperature of the ion source front part and that the mass spectrometer measures the composition of the undisturbed gas flow. Stability and angular dependence of the ion source signal are analyzed. The light emission from the cold ion source in an arc heated supersonic flow is discussed.