After their end of operation, the four Cluster-II satellites are re-entering the Earth's atmosphere. The first Cluster-II satellite, named Salsa, re-entered on the 8th of September at 18:46 UTC (2024-09-08T18:46 UTC) over the South Pacific, approximately 2000 km west of Easter Island. An airborne observation team was on station aiming to observe the satellite's break-up. This paper reports the design and execution of the airborne observation under the challenging situation of an entry under plain daylight conditions. The mission planning and preparation in coordination with the observation prediction leads to the flight mission details. Due to the highly eccentric orbit, the entry predictions were particularly challenging and resulted in a wider spread of potential entry corridors. Therefore, based on the very last perigee, only 52 h before the actual entry, and spacecraft data after the maneuver, the team received the last orbit information at 20:30 UTC on the 7th of September (2024-09-07T20:30UTC). Based on this data an appropriate flight path for the aircraft was designed. On board a Falcon 900 business jet, the team deployed six different stations with a total of 26 cameras. All cameras were time-synchronized to the GPS time using a centralized time server. The mission was successful. The infrared cameras detected the entry for approximately 23 s beginning at around 18:47:08 UTC.

The ESA-TRP SPADEXO project investigated the use of thermites to provide additional enthalpy to a spacecraft re-entering towards the Earth, with the objective of limiting its casualty risk on ground. Steel mock-ups inspired by the geometry of solar array drive mechanisms were filled with thermite and placed in DLR's L2K arc-heated hypersonic wind tunnel. In each of these samples, a set of thermocouples was installed to monitor ignition and propagation of the heat generated by the reaction. One of the thermocouples was placed in a hole machined inside the mock-up wall to monitor temperature evolution in proximity of the pyrotechnic charge, without the risk of losing the sensor due to the ignition of the thermite. The main objective of these tests was to study the dependence of the heat transferred from the internal charge to the surrounding structure from the filling level. Results showed that higher thermite filling resulted in higher transferred enthalpy. In the presence of a large thermite amount, the reaction led to the formation of a dense liquid drop close to the side wall, causing significant heat transfer towards the wall of the mock-up. Tests were rebuilt using the SCARAB re-entry software, extended with a dedicated model to represent the ignition of an internal charge. Ignition and heat transfer were adequately described by the model in most of the test configurations. Specific parameter tuning was needed for the highest filling factor tested in this work, highlighting the influence of reaction products internal dynamics on the heat transfer processes.

This report provides insights on the current state of understanding of hazards associated with space vehicle reentry and their prediction and regulation. Topics discussed include. center dot Current regulations and guidelines that limit hazards to people from a single object reentry and describe recent desires to minimize hazards associated with reentries of multiple satellites from individual large constellations. center dot Tools and material data that are used to model reentries and estimate ground hazards. center dot Issues associated with object-oriented and spacecraft-oriented reentry prediction tools. center dot Uncertainties that affect the ability to predict where and when an object will decay from orbit and reenter the atmosphere, and. center dot Flight experiments that collect data to help understand reentry breakup and improve hazard prediction models. The report provides recommendations for future work and next steps that should be considered to improve models and reduce reentry hazards as new space systems emerge and evolve.

In compliance with ISO 24,113 and ESA Space Debris Mitigation requirements, spacecrafts in Low Earth Orbit (LEO) must be removed from their operational orbit within 25 years and re-enter the Earth's atmosphere having an on-ground casualty risk lower than 1 in 10,0 0 0. To maximize the number of uncontrolled re-entries, which have much less impact on system mass and costs, ESA's Clean Space initiative is investigating design for containment (D4C) techniques and collaborating with European industries and space agencies to assess, model, analyse, and test new concepts through re-entry tools and plasma wind tunnel experiments. The main objectives are to understand the survivability of materials and techniques suitable for different containment concepts, to improve re-entry modelling, and implement effective D4C measures. This paper shows the results of these activities, that have been the first milestones in the knowledge of D4C, although further investigations are needed. (c) 2023 International Association for the Advancement of Space Safety. Published by Elsevier Ltd. All rights reserved.

In the frame of the ESA-TRP SPADEXO project, the use of thermites to aid spacecraft demise during re-entry is under investigation. The charges are expected to ignite spontaneously during the reentry phase, supplying additional heat to components critical for the on-ground casualty risk. This concept was explored experimentally in DLR-Cologne’s L2K facility, where steel mock-ups filled with the energetic material were exposed to relevant conditions for the final application. In this paper, the selection of the pyrotechnic material will be discussed, as well as the macroscopic results obtained during the experimental campaign for one out of the three geometries explored during the project. XRD and tomography were then used to characterize the slag produced during the tests, and to explain the reasons of the unexpected pressure build-up observed during the tests involving a fraction of activated thermite.

The use of thermite to aid spacecraft demise during atmospheric re-entry has been investigated in the ESA-TRP SPADEXO project. An experimental campaign in DLR’s L2K arc-heated wind tunnel facility was dedicated to explore the Thermite-for-Demise concept. Steel mock-ups of a ball bearing unit, partially filled with thermite, were placed in L2K. The breadboards were then exposed to an air flux simulating the typical conditions that characterize spacecraft re-entry. In this paper, the key results of the tests are presented. The dispersion of a mechanically activated fraction of thermite proved to be effective in controlling the overall charge ignition temperature. Thermite-induced demise was experimentally verified in the wind tunnel. The SCARAB software was extended and used to rebuild the retrieved thermal data. The results of the simulations were in good agreement in both predicting the ignition timing and the effects of the thermite charge on the sample.

We computed the ablation of different spherical artificial meteoroids entering from a low-Earth orbit in the context of the AllBert EinStein mission. AllBert EinStein is intended to reenter spheres of known size and material into the atmosphere to determine the percentage of kinetic energy converted to light. This paper models the reentry to predict magnitude curves for the different initial conditions. An emphasis is placed on determining the difference between the single body ablation model and ESA's reentry software SCARAB. It is also shown how the CFD simulations can work in synergy with SCARAB results to increase detail in the airflow regime around. Our study shows that with few fixes the meteor method replicates with good accuracy the SCARAB results for different artificial meteoroids, showing the validity of both tools.

The use of thermite to assist satellite demise is a novel methodology under exploration in the frame of the CleanSpace Initiative of the European Space Agency. The idea consists in inducing an additional heat source during the reentry of a spacecraft, supporting the destruction of those massive components which may not demise completely. Embedding thermites into some components is under investigation within SPADEXO, an ESA-TRP project. One of the key aspects of the energetic component design is the understanding of the best heat transfer mechanism. This paper presents a preliminary on-ground experimental campaign aiming at the quantification of the heat exchanged between a thermite charge and a surrounding metallic structure. This activity aims at demonstrating the capability of spontaneously igniting a thermite charge embedded in a metal vessel subject to external convective flow as well as evaluating the efficiency of the heat transfer process.

Since March 2014, all ESA satellites and launcher upper stages which will be disposed of by atmospheric re-entry at the end of their operational life must demonstrate that the risk from fragments surviving the re-entry and causing casualties on ground is less than 1 in 10,000. This casualty risk is calculated by re-entry tools simulating the uncontrolled re-entry event using a computer aided design model of the spacecraft. The uncertainties on several parameters such as the aerothermodynamics fluxes model, the structural interfaces model, the materials model, and the level of detail of the spacecraft architecture will have an impact on the re-entry event simulation and the associated casualty risk calculations. To better understand the uncertainties associated to material modelling, five materials often used on space missions were tested in Plasma Wind Tunnels, mimicking atmospheric re-entry environment. Thermo-physical properties, thermo-optical properties and mechanical properties at high temperature were also characterized. Analysis of the samples after plasma wind tunnel tests was performed. A database compiling the materials properties measured and the plasma wind tunnel test results was created. The material properties characterised and generated during the activities will serve as inputs for the re-entry simulation events at equipment and system level.

The high-fidelity re-entry break-up simulation software SCARAB (SpaceCraft Atmospheric Re-entry and Aerothermal Break-up) is currently being upgraded with new models for aerothermodynamics and material ablation. The capabilities of SCARAB are extended to improve the support of Design-for-Demise (D4D) methodology modelling and uncertainty quantification. A set of newly implemented features for the so-called measurement evaluation support (MES) provide the functionality to rebuild static flow conditions of wind tunnel experiments and Computational Fluid Dynamics (CFD) simulations and extend the SCARAB re-entry simulation with options for fixed attitude and reference trajectory input. The new models implemented are validated with recent data from wind tunnel experiments, re-entry observations and CFD, using the new MES capabilities. This paper provides an overview on the new SCARAB models and extended functionality.

According to international safety guidelines, the on-ground casualty risk for a re-entering object shall not exceed 1 in 10,000. The casualty expectancy can be reduced in two ways (1) by selecting a suitable impact area and population density within, or (2) by reducing the casualty area from the surviving fragments. Due to the cost associated with a controlled targeted re-entry, the latter option has attracted a lot of attention. To achieve the requirement of reducing the casualty area, the number, size and kinetic energy of the surviving fragments have to be limited. The fragments which survive re-entry are often from recurring spacecraft components (e.g. propellant tanks, reaction wheels, solar array drive mechanisms, magnetic torquers, etc.), therefore the interest of applying designs which increase the demisability of these components is high. Understanding the demise process during re-entry helps in identifying feasible design-for-demise options. For this study, we conducted re-entry risk analysis of two critical spacecraft components, a solar array drive mechanism, and a reaction wheel using a spacecraft-oriented re-entry tool, in order to assess the break-up and demise behaviour of the components. Detailed models of the components were created using design input from the manufacturers and initial conditions for the simulations were selected within a release window (58–98 km) along a reference trajectory. We have investigated the casualty risk metrics for the components, derived the most-probable casualty area over release altitude and investigated its uncertainties. Together with the manufacturer, we identified feasible design-for-demise options for the components and evaluated their impact on the casualty risk.

The concern about the on-ground risk caused by spacecraft fragments surviving atmospheric re-entry has significantly grown during the past decade, resulting in numerous activities of the space community like re-entry simulation tool development, improvement, and validation, as well as research for design-for-demise (D4D). The purpose of the first group is to increase the confidence in numerical re-entry risk predictions, while the second activity aims to develop new spacecraft design techniques which are likely to improve the demise behavior significantly.