One consideration is formation of air plasma in the beam (dielectric breakdown) between the transmitting array and the vehicle. If that happens, the plasma will absorb power, blocking it from the launch vehicle. Kind of the microwave analog of LIBS (https://en.wikipedia.org/wiki/Laser-induced_breakdown_spectr...).

The breakdown field strength of gases decreases as pressure declines until a minimum of a few Torr (see Paschen's Law: https://en.wikipedia.org/wiki/Paschen%27s_law).

The power density in a beam focussed on a launch vehicle would be pretty high. Anybody know if air can sustain beam propagation at the E-field gradients that would be needed for this to work?