ABLAMOD

Advanced Ablation Characterization and Modelling

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 Obiettivo del progetto (Objective)

'As mentioned in the FP7 space call for Europe to be active in space in the long term, be it in earth-orbit or across the solar system, it is essential that space technologies with key capabilities are at its disposal. This goal requires developments by radical innovation which may then lead to “disruptive technologies”. In this frame new thermal shielding and low risk return strategies are defined as European key activities in the future. In Europe the design of spacecraft for high-energetic interplanetary or sample return flights is still performed with big safety margins, which means high mass. This again leads to higher costs and a reduction in scientific payloads or instrumentation. Ablative thermal protection materials are a key technology for current and future space exploration missions. However, the mission feasibility is determined by the materials available, and the development of new materials is performed, essentially, by an iterative trial-and-error process. This is due to the absence of validated predictive models for ablative material behaviour – models are tuned to bulk material properties from tests. For each new material, this tuning has to be redone because the models are not of sufficiently high fidelity to be able to make even small extrapolations. This means that materials cannot be designed to a specification to fulfil the needs of a particular mission. The aim of this project is to make a substantial step towards a predictive model of an ablative thermal protection system by incorporating aspects of high fidelity mesoscale ablator physics within a modular framework. In order to successfully develop such physics modules, the understanding of the fundamental processes occurring within the ablative materials must be improved. To this end, existing ablative materials will be tested in the most powerful European long duration high enthalpy facilities using both standard instrumentation and advanced measurement techniques. From the data obtained, and the state-of-the-art knowledge of ablator physical processes, modules for the specific processes of internal gas flow, internal radiation and gas-surface interaction will be developed to fit inside an overall multi-scale ablator modelling scheme. The improvements made in the representation of an ablative material will be validated against the ground testing, and this advanced ablator model will be applied to realistic flight configurations to demonstrate the impact of the enhanced physics on the understanding of real ablator performance. The existence of this capability will allow improvements in the efficiency and cost of developing advanced new ablative materials which are tailored to meet the specifications of Europe’s future mission needs. In order to reach this objective, the ABLAMOD project brings substantial expertise from across Europe in ablator materials, thermochemistry, microfluidics, entry systems and instrumentation.'

Introduzione (Teaser)

Because of the absence of validated predictive models, today most ablation materials are developed by an iterative trial-and-error process and are not in line with the latest safety rules. An EU-funded project develops key technologies for improvements in efficiency and cost for a new generation of high temperature materials.

Descrizione progetto (Article)

One of the biggest challenges of space transportation is bringing back a spacecraft to Earth or achieving safe entry and landing on other planets. During the atmospheric entry phase of the flight the vehicle is exposed to extreme thermal loads. In the dense atmosphere of a gas giant like Jupiter or Saturn these loads can be two or even three orders of magnitude larger than those of an Earth re-entry. The development of more efficient materials is essential for interplanetary missions like ExoMars or sample return missions.

One way of managing thermal loads on a spacecraft, caused by the enormous speed of re-entry, is to protect its structure with a sufficient thermal protection material. The most efficient method is the thermal ablation process, which blocks the heat transfer due to the phase transformation from solid state to liquid and gas. Gaseous ablation products remove heat from the surface during the outgassing process.

However, most ablation materials currently available are the results of research carried out more than 20 years ago. Recently Europe intensified the effort for the development of new generation ablation materials. Main objectives of the EU-funded project 'Advanced ablation characterization and modelling' (http://www.ablamod.eu/ (ABLAMOD)) are better material characterization, improvements in physical modelling and measurement techniques.

The ABLAMOD team investigated three main ablators based on carbon phenolic, silica phenolic composites and cork. Novel spectroscopic techniques are used to characterise the high enthalpy flow properties and material behaviour under extreme aerothermal environments. Complementary measurement techniques allow the determination of material properties like density, thermal conductivity, heat capacity and thermal expansion at different levels of the ablation process.

The collected experimental data serves as a starting point for the development and validation of realistic models for ablation processes. ABLAMOD researchers develop modules for gas-surface interaction, transport phenomena and radiation. The modularity of the coupling tool of these modules and the main ablation code allow very flexible simulation with different time scales. ABLAMOD's approach for ablation modelling is unique in Europe. Through a better understanding of the underlying physics, a significant step is expected to be made towards a predictive ablation modelling framework, allowing the tailoring of materials for a specific mission.