The system of differential equations for the non-ablated mass, the
average implosion velocity, and the ablation radius of an indirectly
driven capsule in acceleration phase, has been obtained from
conservation principles of hydrodynamics. Two phases are distinguished
during acceleration, according to the uniformity of the velocity in the
non-ablated shell. The results of the integration of this system are
well compared with numerical simulation of optimized capsules. Assuming
that the ablation pressure depends only on the Hohlraum temperature,
the relations between the non-ablated mass, the implosion velocity, and
the ablation radius are obtained for optimized temperature shape. These
relations provide the maximum implosion velocity and the remaining
non-ablated mass in terms of the initial capsule and the maximum
temperature (or the initial capsule mass in terms of the remaining
non-ablated mass) useful to determine the required ablator thickness
for optimized capsules. These results are also compared with numerical
simulations of different capsules.