Numerical-experimental cross-correlation and Technology assessment

Numerical rebuilding

Validation of the numerical models is another objective of the test campaign, and it is a critical aspect to increase the robustness of the inflatable heat shield design process and the extrapolation of results to flight. Within EFESTO-2,
the following areas will be covered:

• Structure: mechanical characterization of inflatable structure is fundamental to feeding models and understanding its behaviour. Mechanical properties of the constituent materials of the IAD have been carried on during the EFESTO project. Within the same project, an early tuning of the structural models has been completed, in order to better predict the complex behaviour of bladder tendons and carriers. Additional tests of EFESTO-2 will be used to validate the updated models with respect to other experimental data. Moreover, the axial symmetric models from the past project will be upgraded to full 3D models suitable to simulate and predict not only the static deformation but also the dynamic behaviour, that is fundamental for an elastic structure designed to operate in a highly dynamic re-entry environment.
• Aerodynamics: aerodynamic stability is usually simulated through CFD, verified in the WTT and then validated again in CFD. Extrapolations to flight, based on ground tests validation are a key point aiming at increasing the TRL of inflatable heat shields in Europe. The experimental data obtained during the WTT of the design definition will allow enriching the aerodynamic characterization of the reference shape with a particular focus on behaviour under deformed condition in critical Mach regimes, thus allowing to extend the CFD simulations' robustness. Moreover, the WTT data will enhance the Flying Quality assessment providing a wide spectrum of investigation of the vehicle flyability during re-entry.
• Flying Quality: due to the entry loads, the inflatable spacecraft is expected to experience a change in shape which ultimately affects its aerodynamic performance, as well as its inertia tensor components. FQA will take advantage of the enhanced modelling provided at aerodynamic and structural levels, and tie accordingly their contributions together with the reference trajectory, allowing to bring light on the static and dynamic stability performance of the spacecraft throughout the return leg.
• Structural morphing process: validation of the inflation process can be achieved by a hybrid analysis-test method, which foresees the implementation of virtual (i.e. CAE/FEM based) models of the IAD, both for the relevant EDL application and for the ground test model. Basically, those two models will differ for what concerns the gravity environment, of course 0-g for the EDL model and 1-g for the ground model. In the case of the ground model, validation will be sought via the correlation between test data and analytical data.

Roadmapping

In the development process for operational space applications, it is always necessary to evaluate starting and ending points of any endeavour. The assessment of TRL is then the baseline subject of that evaluation. Together with that, it is also important to draw a path over which is defined as a clear way to arrive at the final target of an operationally implemented technology or solution. Therefore EFESTO-2 will also cover that task by carrying out first a technology assessment with the objective of identifying the reached TRL, and second defining a roadmap for near-mid-term development that might enable to reach the TRL7/8.in the field of IAD. The roadmap will encompass the whole verification, validation and qualification effort including numerical, ground testing and flight testing. Cost estimation will be also done for such a long-term vision.