Relativistic Space Travel: Optimizing Proper Time [Project Hail Mary]

[PeterDonis]

the mass ratio calculations don't actually seem to support the top speeds required for the courses described in the book.

Using the formulas I gave in post #30 just now, if we know the maximum rapidity $\alpha$, the proper time $T$ required to reach it at proper acceleration $a$ is given by

$$
T = \frac{\alpha c}{a}
$$

Plugging in $\alpha = \ln 21$ and $a = 1.5 \text{g}$, I get $T = 1.97$ years. That looks consistent with the time you gave in the OP.