You did not list anything that stops those missions. They were, and are to this day, feasible. More than that, they are history.
I'm going to be harsh here: Only a deep idiot could believe these missions did not occur, let alone regard them as impossible now. There just isn't anything to stop them.
If they are feasible then everybody will be doing it soon.
Thing is, they aren’t and they won’t be.
Get ready for a bunch of “dog ate my homework” excuses for years and years and years.
We have had fifty plus years of them so far....