Yes, it *is* impossible, but only for the privileged few.
If sustained space travel is so possible then you should be able to demonstrate it for us.
OK, I was originally making an attempt at humor.
Obviously I cannot actually, personally, demonstrate space flight. Instead I have been force to make a judgment, based on the evidence available to me, that space flight is probably possible.
Most recently this evidence includes observing the ISS several times and reading about other people's observations, and amateur pictures, of the ISS from around the world.
I also subscribe to Sky satellite television, which requires a dish to be pointed to a specific part of the sky. This has been the case for 5 years. I know the dish is highly directional because it was moved by a strong gust of wind last year and require re-alignment. I know of no other technologies which can maintain an object is one part of the sky (with strong jet-streams) for 5+ years.
Please feel free to provide any explanation for the above, citing specific examples of current craft which match the attributes I have described, in terms of speed and endurance.