Speakers
Description
Reducing the risk of casualties from debris uncontrolled re-entry is of major interest. It requires advancing the knowledge of space debris degradation during their re-entry and strengthening the predictive capabilities of the high-fidelity and spacecraft-oriented numerical tools and material response solvers.
To fulfill this target, various materials have been identified to be analyzed and characterized to provide insight into degradation and fragmentation processes and enrich the current ESA ESTIMATE database, namely Haynes 25, Steel AISI 304L, and CFRP.
Providing materials properties and tools able to model their atmospheric re-entry is capital since much debris found on the ground are made of these materials.
Given this background, the global objectives were four-fold:
- Provide a database of experimental conditions and observables
- Develop or enhance the flow and material response codes and their coupling
- Predict the experimental measurements
- Derive accurate, cost-effective, and ready-to-use engineering models to support the manufacturing and design-for-demise of materials, andsystems used for launcher and satellites
The project starts with an extensive experimental campaign undertaken in four different facilities (CNRS-PROMES, ONERA, CORIA, and VKI) to measure, infer the bulk properties of the aforementioned materials and characterize with various diagnostics the key mechanisms governing their thermal response and demisability.
An explicit coupling strategy (called NEVADA C.T.) consisting of in-house RTech’s high-fidelity tool Mistral with material response solver PATO based on OpenFOAM is adopted to provide a cross-check verification code for spacecraft-oriented tool and to rebuild numerically the experiments in the VKI facilities. Material in-depth models developed at Coria are implemented in PATO to compute the degradation of metallic alloys and a dedicated high-fidelity composite model is implemented in the spacecraft-oriented PAMPERO tool developed by CNES in collaboration with RTech to improve the accuracy of the predictions.
The objectives of the current study were to advance the knowledge of space debris degradation during their re-entry and to strengthen the predictive capabilities of the high-fidelity and spacecraft-oriented numerical tools currently in use and rebuild numerically the data measured in high-enthalpy facilities and reactors operated at representative flight conditions.
An extensive effort has been made to develop such tools/models in terms of accuracy and CPU optimization. The rebuilding activity allowed us to improve our tools, especially the new version v3 of PAMPERO shows good agreement with the experiments in terms of mass, recession rate, and front and back face temperature. NEVADA C.T. and PAMPERO show good agreements and PAMPERO allows a great speed up for thermal response computation (1-2 months computation for NEVADA C.T. against 1 day for PAMPERO), allowing to handle industrial cases. As a lack of material properties at really high temperature were identified (due to technical issues to measure such properties at high temperature), PAMPERO could be used as an optimizer in order to deduce reliable laws at high temperature.
The key results are presented below with a comparison of with a comparison of front face and back face temperature and the stage of degradation if applicable (for steel and CFRP)
1 CFRP
The final results obtained for CFRP material are presented below. A front surface temperature mapping, qualitative and quantitative ablation comparison, and front/back temperature comparison with experiments are provided below. The simulation is in good agreement with the experimental data.
The final goal, aiming to provide a code to reduce the uncertainties on the risk of casualties from uncontrolled re-entry was fully fulfilled during this activity.
The study shows that significant effort is still required to correctly characterize the thermal properties of composite (especially in a degraded state at high temperatures) and to take into account phenomena such as swelling and delamination.
Further effort will be made on these points to assess the full degradation process of industrial geometries.
