There are a couple of bits of evidence of space travel that intrigue me: (1) the use of ultra-high frequency radio. This means radio waves higher freq than shortwave; one distinction is that these don't bounce off the ionosphere, so they're useless for shortwave/inter-continental broadcasting, they simply go in straight lines, straight through the atmosphere into outer space. It's the sort of radio that NASA (and all the other rocket and space programs of all the countries) uses and when the moon landings and the international space station events were happening, laboratories and radio engineers and hobbyists all over the world tuned into those ultra-high frequencies and heard at least one side of the back-and-forth transmissions. This would not have been possible with conventional shortwave. It means that the radio signals came from outer space, where the astronauts were supposed to be. (2) the retroflector on the moon. Each NASA moon landing, from the very first, set up a retroflector. This is a rather carefully made, very carefully positioned, multi-angular mirror, designed and made specially, which will reflect laser beams and microwave transmissions back to Earth to the very spot from which they were sent. It doesn't have any moving parts nor a battery, but it has to be set up and aimed back at Earth very precisely - more precisely than mere robots could be trusted to do. When the first moon landing occurred in 1969 a bunch of observatories and labs were prepared, already beaming at the landing point ... but not getting their signals returned until the astronauts had finished positioning the retroflector. Since then, a retroflector has been set up by each moon landing; since they don't have any moving parts nor batteries, they're the only things still functioning on the moon. And they could only be functioning there because astronauts put them there. And also (3) demonstrations and stunts by the astronauts: Every moon landing, and even many orbital missions that were not moon landings, the astronauts do something on the television cameras that simply couldn't be done in a movie studio - like hitting a golf ball a mile. This was deliberately done to prove they were on the moon.
Now, the next part is important, consider this: Suppose NASA is lying and somehow the Earth is flat and all that outer space stuff is fake. Why was EVERYBODY fibbing about it before 1958, before NASA was established? Who was raking in the round earth money before NASA? And even now, even if NASA is lying, all those other countries - even the ones hostile to us and not getting any money, like North Korea - also claim the earth is round, also say there were moon landings. There isn't enough money to bribe them all! The Watergate conspiracy couldn't keep its lid on for a full six months and it only involved about a dozen people. How could a conspiracy to conceal the flatness of the Earth succeed for so many centuries, with the complicity of so many scientists and teachers and airline pilots in so many countries, etc. etc.? They couldn't all be bribed or bullied, could they?