In this paper the importance of using accurate CFD simulations in the design of hypersonic vehicles is stressed.
The attention is focused on the one hand on the need to providing the vehicle designer with the estimated error bars
together with the nominal values of the design parameters. On the other hand it is underlined how, in the different design
phases, different levels of accuracy can be used, from simple inviscid computations to complex viscous non-equilibrium
modellization, depending on the problem that must be solved. Then, the attention is focused on the kinetic models, from
the classic macroscopic to the advanced models based on the state-to-state approach. Some examples of test cases that
were used in the last years to validate CFD codes with respect to the kinetic modeling are presented, with the aim of
emphasizing the potential advantages in using the state-to-state approach. Finally, preliminary results of the numerical
rebuilding of wind tunnel test cases that are currently being performed in the framework of the Phys4Entry Project for
code validation are shown.