I remember from the movie that the crew was suspended in a liquid that fills their lungs to protect them from the high acceleration of the ship (I think 20 or 40 g were mentioned?)
This made me curious. Given that the problem with space drives normally is that the more effective ones give only poor acceleration, what did they use? I'm not sure, but I remember that the crew is only suspended at the start and the end of the journey. So acceleration is only at the start and the end.
Does this make any sense? Wouldn't it be much more effective to use fewer "engines" and a decent acceleration throughout the whole journey (with face changing in the middle)? The journey time wouldn't even be much longer — or even shorter, because fewer engine means more space for fuel which means higher end velocity, which will break even higher acceleration and lower end velocity soon.
Out of universe I think they need a reason why the crew was not able to question Dr Weir during the voyage. (But that would as easily be done by hibernation because of food resources, boredom, etc.).
But is there in-universe information about the propulsion technique they use and why they use such high acceleration?