Ground to Flight Investigations of Hayabusa with Ablation Effects

Thermal protection systems (TPS) are of extreme importance for the survival of space vehicles especially during superorbital re-entry to Earth. The design of thermal protection systems requires in-depth knowledge of the thermal loading experienced during a re-entry. The thermal loading data is mostly determined using ground testing and can be backed up by modelling activities including computational fluid dynamics (CFD). The verification of this data with flight data is invaluable and a recent, rare example of an opportunity for comparison was the Hayabusa asteroid sample return mission, which landed in Australia in 2010. During this re-entry a team of international scientists collected spectral data which can now be used for comparison and verification of ground test and modelling/CFD data. Ground testing of subscale models at flight equivalent hypervelocity flow conditions (8 − 12 km/s) can be performed in hypersonic impulse facilities such as the X2 expansion tunnel at The University of Queensland. A recently developed method at The University of Queensland enables heated reinforced carbon-carbon (RCC) models to be tested at temperatures repre- sentative of those experienced in flight ( 2000 − 3000 K), in addition to testing with cold-wall metallic models. Hot wall testing allows more realistic simulation of re-entry flow characteristics including important thermal surface effects (surface chemistry, catalycity) which has previously not been possible. The eilmer3 compressible flow CFD code is used extensively for simulating atmospheric re-entry vehicles at flight and laboratory conditions. Simulations of the Hayabusa aeroshell incorporate heated walls, as well as surface catalycity, to accurately model the conditions experienced by the TPS. These simulations can be coupled with SACRAM, a 1D ablation modelling code, to include the effects of ablation and recession at critical points on the model surface. Current work is investigating the effects and validity of heat flux scaling correlations applied to a range of scaled models with the Hayabusa geometry and flight equivalent flow conditions. This will be achieved through results of CFD simulations, incorporating radiation and ablation modelling, and expansion tunnel testing with hot and cold wall models. Increased understand- ing of scaling methods will allow higher fidelity heat loading data to be acquired allowing more efficient and effective design of TPS. This paper will discuss results from CFD simulations coupled with ablation modelling and modelled surface chemistry. An outline of planned experiments in the X2 expansion tunnel, including background on the RCC heating method and condition development, will also be presented.