Ok. For the arguments sake let's say space travel is not possible. (purely for argument sake. I still believe space travel is not an illusion)
Why would part of the illusion be in convincing the public that the earth is spherical? If what is being claimed by FE's as proof to support a FET is so obvious. Why has so much time and money been spent on supporting a consipiracy of the world being spherical?
I can see a reason why creating an illusion of space travel could be advantageous. I cannot see a reason for concealing the truth regarding the planet is spherical.
P.s. In regards to your comment about Antarctica being ice on top of Rock. You are right, I don't know why I though it would ice all the way down. My mistake. (Although I still disagree that Antarctica is an ice wall around a flat earths perimeter for the record)
The only viable option, in my opinion, as to why the FES disbelieves anything to do with space travel centers around their belief in how gravity works.
They believe that the FE is flying through space at a constant rate which keeps everything pinned to the ground (their theory of gravity).
If you take this view a space ship could never be launched for one of two reasons.
1. The space ship would have to be launched at a speed which would have to be orders of magnitude more than the FE travels through space. Otherwise it would never leave the ground or would shortly be overcome by the FE.
2. If a space ship were launched tangentially to the FE the FE, in its constant forward motion, would leave the ship behind in very short order and the ship would never be able to make it back to the FE.
A third, less viable, option is that they didn't see it with their own eyes so it's all fake. Such is the zetetic worldview.