A note on the generation of fluctuations by Space Shuttle exhaust in the ionosphere

In a recent attempt to understand the enhanced backscatter from Space Shuttle exhaust in the ionosphere, Bernhardt et al. (1995) conjectured on the possible excitation of dust acoustic waves. The condensation of the water vapor of the expanding shuttle exhaust plume into ice grains, and their subsequent charging, may create a dusty plasma in which such modes may exist. In this brief report, we point out that for the parameters as reported by Bernhardt et al. (1975) instabilities on the dust time scale may occur.