Photon-rocket fuel for acceleration and braking
= Photon-rocket fuel for acceleration and braking
{title2=$M_f/M_i=e^{-2\eta}$}
Accelerating from rest to <rapidity> $\eta$ and braking to rest requires two separate photon-rocket burns. Their mass ratios multiply, giving $M_f/M_i=e^{-2\eta}$. For ideal equal-mass matter–<antimatter> annihilation, the initial <antimatter> mass fraction is $(1-e^{-2\eta})/2$. Braking fuel must be carried and accelerated during the first burn.