A widespread misunderstanding within the flat-Earth victims is related to velocity/speed. They seem to think velocity is absolute, while in reality it is measured from a specific frame of reference. Example:
“If the Earth is in motion around the Sun at 30 km/s, and Apollo traveled at only 11 km/s, then how could Apollo astronauts possibly make it back to the Earth?”
We used to measure velocity/speed relative to the surface of the Earth. But it is not always like that.
If a train is moving at 60 km/hour, then we can say it is 60 km/hour relative to the surface’s frame of reference. If inside that train a person is walking towards the back of the train at 5 km/hour, then we can say it is 5 km/hour relative to the train’s frame of reference. To a person outside the train, it would appear the person inside the train is moving at 55 km/hour.
Apollo has the top speed of 11 km/s. Obviously, this is 11 km/s relative to the Earth’s frame of reference. If the Earth itself is in motion around the Sun at 30 km/s, then it wouldn’t be relevant. Before the launch, the Apollo itself is moving at the same speed as the Earth itself, relative to the Sun’s frame of reference.
Apollo only needs to change its speed relative to the Earth if it is to reach the Moon.
Even we are all in motion at 30 km/s if measured from the Sun’s frame of reference. The same thing happens with a person sitting on a train. It would appear he/she is moving at the same speed as the train when observed by a person outside the train.