In the SyFy mini-series Ascension, as one of the plot points reference is made to the Ascension space ship reaching a "Rubicon Point" at which it will take more resources to return to Earth as opposed to continuing the remaining distance to the Proxima system. I.e. it is perceived as a point of no return. However, out of an approximately 100 year journey, wouldn't that have occurred much earlier? I am looking for an in-universe explanation of why that would not be the case.
I am assuming the Ascension is accelerating at some percentage of ~1g to maintain the appearance of an Earth gravitation. The ship is not spinning. Too, the appearance inside the ship seems to have something approaching Earth gravity. As such, after 51 years, the ship is traveling at or near its maximum expected speed. Note, this is supported by the scene during the radiation storm when the question is asked "why should this storm be any different?" The response is that the ship is now traveling faster than it ever has, thus the radiation will have more impact.
However, if that is so, then wouldn't the ship be expected to require another ~50 years of DECELERATION at the same level of ~g to slow the ship down as it approaches the Proxima system? Too, if that assumption is correct would that not also imply that it would take at least 50 years to slow down enough to then be able to THEN reverse course to return to Earth making?
If that is correct, then wouldn't the true Rubicon point on an estimated 100 year journey actually be at ~25 years give or take? 25 years accelerate, 25 years to slow down, 25 years to reverse course to Earth, 25 years to decelerate going back to Earth?
The only thing I can think of which might mitigate this is if the plan is to somehow use the Proxima system stars in series of gravitational slowdown maneuvers at higher than 1g effects rather than simply decelerate for 50+ years. But, I would think to shed that much speed in a short time after reaching Proxima would require a significant increase in the "perceived" gravity within the ship. More than what would be expected people could take for an extended period of time. Remember there are babies and small children on board as well as presumably elderly.
BTW, though I am not good enough at the math to show it, I am setting aside the fact that after 50 years of ~1g acceleration, wouldn't the ship be traveling at an appreciable fraction of the speed of light, hence relativistic effects would start to become noticeable as well?