I. Introduction

The ONERA F4 wind tunnel is a ground testing facility allowing simulation of hypervelocity airflow involved with the aerobraking of space vehicles during their reentry into planetary atmospheres and particularly the Earth's atmosphere. Wind tunnel testing still plays an absolutely necessary role throughout all phases of adjustment of the aerothermo-dynamic design of aerospace vehicles.1 The quality of the simulations is governed by so-called "similarity laws" with pertinent dimensionless parameters Mach and Reynolds numbers are in current use for classical wind-tunnel tests, which is a test on the model of a conventional aircraft deemed "correct" if the ground simulation is performed at the Mach number of the flight with a Reynolds number not too far from full-scale. These similarity conditions are performed in large, classical facilities.

A space plane, when reentering Earth's atmosphere, passes through several different flow regimes, each of them being governed by different similarity laws and therefore often requiring specialized test facilities for representative simulation (Fig. 1). Coming down initially through a zone of very low ambient air density using jet control, the vehicle experiences increasing density. Aerodynamic phenomena start in the hypervelocity regime, where the speed is such that nitrogen and oxygen molecules are dissociated (split up into atoms) behind the bow shock caused by the...