RF ionization rates for mixtures of air with barium are computed using a Fokker-Planck code. It is shown that there is an optimum mixing ratio of barium to air, significantly lower than unity, which maximizes the ionization rate for a given value of incident RF power density and frequency. Rocket injection of barium at a selected height reduces significantly the RF breakdown threshold for the mixture, and allows atmospheric and ionospheric breakdown at the selected heights using the radiation from the powerful HF radio facilities. The possibility of field experiments using currently available or projected HF heaters is discussed. ¿ American Geophysical Union 1993