A novel approach for the accurate simulation of re-entry fragmentation

The evaluation of the on-ground casualty risk assessments due to a controlled/uncontrolled re-entry is highly sensitive to the accurate prediction of fragmentation events during an atmospheric re-entry. Accurate knowledge of re-entry fragmentation becomes all the more important for Design for Demise (D4D) procedures to ensure compliance of future missions with Space Debris Mitigation guidelines for small and medium satellites. To address this issue, we propose a novel approach to study fragmentation during re-entry. The new peridynamic theory provides the capability for improved modelling of progressive failure in materials and structures. Peridynamics is a non-local continuum mechanics formulation developed in the early 2000’s. The governing equations of peridynamics are integro-differential equations and do not contain any spatial derivatives, which provides a very attractive formulation to simulate problems including discontinuities such as cracks. The emergence of fully coupled peridynamic thermo-mechanical simulations in the recent years may provide an accurate methodology to study re-entry fragmentation in a single framework for multi-physical simulation modelling. For this work, we use an open-source peridynamics software that has been loosely coupled with an object-oriented re-entry analysis code. The main objective is the study of start and propagation of a crack, during a re-entry conditions. We model a test case spacecraft with a junction made of a single metal, and run the simulation for various initial conditions and junction thicknesses. We analyse the subsequent break-up of the junction and compare it with the break-up criteria used by some of the state-of-the-art re-entry simulation codes. We also discuss about the development of the relevant framework and coupling methodology to enable such simulations

Initial conditions of a novel CubeSat during atmospheric re-entry

Despite the establishment of Design for Demise (D4D) as a debris mitigation process, little is still known about the conditions under which debris fragment or survive during re-entry. STRATHcube, a student-led CubeSat project for Space Situational Awareness developed at the University of Strathclyde, aims to contribute to the development of D4D through its secondary payload, providing data on the aerothermal conditions and forces experienced by the satellite during fragmentation upon atmospheric re-entry. The experiment is underpinned by the satellite’s stability during re-entry and until fragmentation, which will allow for data to be transmitted in real time. This paper focusses on the configuration of the solar arrays of the CubeSat and on its attitude during re-entry. Their effect on the operating conditions of the components necessary for recording and transmitting data is explored through a low fidelity model constructed within ESA’s Debris Risk Assessment and Mitigation Analysis (DRAMA) tool. Temperature data obtained from this model during the aerothermal demise of the solar panels are also used as a reference point for the design of the thermal protection system. This analysis will advise the requirements of the deorbit manoeuvre of the CubeSat, the alignment of its solar panels for re-entry, and of the thermal protection components necessary for the success of the experiment

Multi-fidelity and multi-disciplinary approach for the accurate simulation of atmospheric re-entry

This paper proposes a multi-fidelity and multi-disciplinary framework that combines low- and high-fidelity aerothermodynamics, thermal analysis, flight dynamics, and structural analysis in a modular approach to achieve a favourable trade-off between cost and accuracy. The novelty in the current study is two-fold: one is to simulate a more accurate destructive re-entry process over using a prescribed altitude trigger for fragmentation, and the other is to implement automatic fidelity switches between high- and low-fidelity models for the aerothermodynamics based on the shock-envelope approximation of Billig's formulation. For the high-fidelity flow modelling, the open-source SU2-NEMO code is used to solve the slip to continuum regimes while the SPARTA-DSMC solver is used for transitional and free-molecular regimes. To estimate the fragmentation altitude, a linear structural analysis of objects modelled as joints are continually carried out using the FEniCS finite elements solver. A temperature-dependent von Mises yield criterion is used to identify failure in joints. The software framework, TITAN Transatmospheric Flight Simulation, is applied to the ESA ATV re-entry and fragmentation test case

Fidelity management of aerothermodynamic modelling for destructive re-entry

The re-entry process is distinguished by the presence of several fragments with intricate geometries resulting from the demise process, which may lead to complex features in the re-entry flow. An example of these features is shock impingement, which leads to highly localized loading of pressure and heat flux on the bodies' surface. These loads impact the overall dynamics and cannot be captured using state-of-the-art low-fidelity approaches. A multi-fidelity approach is considered to reduce the uncertainty in predictions during a multiple body re-entry. Such an approach allows the usage of low-fidelity models along with high-fidelity methods such as Computational Fluid Dynamics or Direct Simulation Monte Carlo. This research investigates the formulation and use of a strategy for the automatic selection of the level of fidelity in the computation of aerothermodynamic loads acting on bodies undergoing destructive atmospheric re-entry. Based on the Billig formula, which provides an approximation for the definition of a shock-wave envelope for blunt bodies, a criterion to automatically detect when to transition from low-to-high/high-to-low fidelity is proposed. In the present work, the focus will be on the application of a shock-envelope logic to switch between fidelity methods, exploring the influence of the shock waves from leading fragments onto the following fragments

A numerical approach to evaluate temperature-dependent peridynamics damage model for destructive atmospheric entry of spacecraft

The evaluation of the on-ground casualty risk assessments due to a controlled or uncontrolled re-entry is highly sensitive to the accurate prediction of fragmentation events during an atmospheric re-entry. The main objective of this study is an investigation into the use of Peridynamics (PD) to improve the analysis of fragmentation during atmospheric re-entry with respect to currently adopted semi-empirical approaches. The high temperatures characterising such scenarios may substantially impact fragmentation, which requires appropriate modelling of the damage process within the PD method. The damage models in PD require experimentally determined fracture mechanical properties that are unavailable as a function of temperature. This work proposes a numerical methodology to estimate the PD damage parameters changes with temperature to enable the study of fragmentation during atmospheric re-entry. Initially, tensile-testing simulation experiments are performed in peridynamics to calibrate material parameters for steel and aluminium alloys as a function of temperature. Then, a parametric study is carried out to evaluate the temperature-dependent damage model parameters for the same materials. The applicability of the proposed methodology is showcased using a re-entry test case scenario

Multi-fidelity approach for aerodynamic modelling and simulation of uncontrolled atmospheric destructive entry

This paper proposes a multi-fidelity approach to the modelling and simulation of destructive atmospheric re-entry of human-made space objects. The presence of fragments, generated during the demise process, and the complex geometries of the objects determine the formation of complex flow features that need to be accurately resolved to limit the uncertainty on the ground impact risk. Critical to the determination of the dynamics of the fragments is the ability to correctly predict aerothermodynamic loads. The paper proposes an approach to the integration of expensive high-fidelity Computational Fluid Dynamics (CFD) solvers with fast low-fidelity methods for aerothermodynamics load calculation, that achieves a favourable trade-off between cost and accuracy. This multi-fidelity aerothermal approach is coupled with a 6-dof dynamic model to determine the motion of the fragments. For the high-fidelity modelling, a quasi-steady approach is used to determine the dynamics of the fragments in the instant following the breakup. The approach is validated with experimental data. Finally, a test case is presented to demonstrate the effectiveness of the proposed multi-fidelity at reducing the uncertainty in destructive re-entry predictions