Throughout the series we see the occupants of Ascension apparently experiencing normal Earth gravity. In deep space there are only two ways to simulate the effects of gravity; either you build a ship that rotates around a central axis, where centrifugal force gives the appearance of gravity at the rim, or you rely upon thrust from the engines. Since Ascension is clearly not cylindrical (all through the series we see flat floors and a deck layout along the axis), the apparent force of gravity must therefore be provided by thrust from the engines.
To approximate the gravity of Earth, the engines would need to provide a constant acceleration of 9.81m/s2. At this acceleration, the ship would reach 97% of the speed of light in just 2 years and the journey to Proxima Centauri (Ascension's quoted destination) would take roughly 5.2 years. In the show, the ship has apparently been en route for over 50 years, almost 10 times as long as the journey should take.
Such a speed would not be possible for a ship of this type in any case, as it would need a huge shield against interstellar material and an impossibly large fuel load.
All of this is simple math and physics and could be questioned by any reasonably well-educated person in the 1960s; it's inconceivable that none of the crew or other people on board would not have questioned this inconsistency.
