Our Mobile Lidar Trailer (MLT) has been deployed to Cape Canaveral Air Station for the purpose of studying the characteristics of launch vehicle plumes in the stratosphere. In addition to measurements of plume extent and dispersion rates, information on particle species and size can be obtained from the wavelength dependence of the Mie return signal. We measure the backscattering ratio of Mie to Rayleigh return at several wavelengths and compare the results to a model of Mie scattering cross sections for homogeneous spheres of specific refraction index and radius. Of primary interest are the calculations for particles which are present in the exhaust of solid rocket motors (SRM) and are conjectured to be instrumental in the catalysis of halogenic destruction of stratospheric ozone. Our data indicate that these particles, at least within the first half-hour after launch, are small (r<50 nm as an upper limit). The data also shows a trend of the mean particle radius increasing with time. ¿ 1999 American Geophysical Union