Travel to Light Speed: Acceleration & Deceleration

[mileymo]

How long/what distance would it take a spaceship (with a hypothetical propellant-less engine) to accelerate to near light speed, and secondly, how low long/what distance would it take to decelerate back to zero again?

 

[BvU]

Hello Mileymo, welcome to PF !

Infinitely long to accelerate and the same to decelerate.

If these answers are not to your liking, tell us some more at what level you are, at what level you'd like to be assisted. Better: pick up some introductory special relativity material and do the exercises -- and ask more questions here. Good hunting !

 

[mathman]

How long/what distance would it take a spaceship (with a hypothetical propellant-less engine) to accelerate to near light speed, and secondly, how low long/what distance would it take to decelerate back to zero again?

It very strongly depends on how near is "near light speed". In addition how large is the acceleration - usually it is limited by mechanical or human constraints - without a limit you can get to near light speed in a very short time.

 

[Vitro]

How long/what distance would it take a spaceship (with a hypothetical propellant-less engine) to accelerate to near light speed, and secondly, how low long/what distance would it take to decelerate back to zero again?

I found this graph on Wikipedia which might be what you're looking for:
https://en.wikipedia.org/wiki/Proper_acceleration#/media/File:Roundtriptimes.png