Hypervelocity impacts of space debris, represented by aluminium spheres, against typical shielding systems for the International Space Station (ISS) manned modules are simulated using the AUTODYN-2D hydrocode. The considered shield type is the double bumper shield, i.e., two separate bumpers placed in front of the structure to be protected. Numerical tools are first tested and calibrated through the simulation of available tests, at the maximum impact velocity currently attainable (around 6.5 km/s). As the estimated debris average impact velocity along the ISS orbit is around 10 km/s, the model giving the best agreement with the experiments is then used for the ballistic limit extrapolation in the velocity range not experimentally achievable. The results of numerical extrapolation are compared with the semi-empirical curves actually used for the ballistic limit estimation in the high velocity regime, based on the assumption of damage proportional to projectile momentum.