What came to my mind immediately was 'Passengers'. But, reading up the plot on W...

eesmith · on Aug 10, 2021

From Wikipedia, 60 light years and "a journey lasting 120 years".

It doesn't say if that's 120 ship years or Earth years. I'll assume ship years as that makes the most sense in context.

Assuming constant acceleration to the 1/2-way point, flip, deceleration, and using http://www.projectrho.com/public_html/rocket/slowerlight3.ph... :

  T = (c/a) * ArcCosh[a*d/(c^2) + 1] (given acceleration and distance)

  60 years = (c / a) * arccos(a * 30 ly / (c^2) + 1)
  1893456000.0 = (3E8/a) * arccos(a * 3.15576 + 1)

Using Wolfram Alpha to solve - https://www.wolframalpha.com/input/?i=1893456000.0+%3D+%283E...

  a = 0.14748 m/s^2 or about 1.5% g

Time elapsed on Earth is only a bit longer than ship time:

  t = (c/a) * Sinh[a*T/c] = 1.15 * ship time ("proper time")

Final velocity at flip is:

  v = c * Tanh[a*T/c] = 0.73 * speed of light