What is the kind of channel seen by a communication system (for telemetry data) on-board a launcher during various phases of launch. Is it a fading channel or AWGN channel? (Additive white Gaussian noise)
First of all, you obviously get Doppler, so that's something that needs to be addressed in a channel model.
Then, as long as you're close to ground, you might be seeing multipath, and hence, frequency-dependent fading.
In every case, even the flat-fading case typically assumed for space comms, you don't get AWGN - you get a complex fading coefficient that describes the attenuation and phase of the channel. Obviously, as the spacecraft moves relative to ground, that thing isn't constant – neither in its phase (which might at least on a larger scale be covered by a Doppler model), nor in its attenuation.
Spacecraft during launch typically shake violently. That can lead to fast phase changes, i.e. phase noise, which leads to noise that is neither white nor Gaussian in amplitude.
So, no, AWGN is not a model that fits here.