Correct Answer : Lack of experimental facility
Explanation : The hypersonic bodies which fly at very high Mach numbers exist today which are tough to analyse experimentally because it is hard to replicate such high Mach numbers in a wind tunnel. The hyperonic flow has very high Reynolds number and tempertaure which is not easy to replicate. For these reasons, engineers resort to the use of computational fluid dynamics to design vehicle flying in hypersonic regime. The results are accurate enough.
