Speaker
Description
Over the past decades, near-Earth space is becoming increasingly congested thus increasing the risk of inter-collision between satellites and generating thousands of space debris. To keep the near-earth orbit usable, it is necessary to deorbit the satellites at the end of their lives. However, during atmospheric reentry, parts of the satellite might not burn up completely and thus pose a non-negligible risk to ground safety. Typical risk assessment tools for satellites reentry are based on simplified geometrical and physical assumptions, limiting their capabilities to accurately capture local aerothermal effects.
Especially, inner components of satellite are shielded from the hypersonic flow during the early phase of the reentry, delaying their burn up. The use of demisable joints, as developed in the TEMIS-DEBRIS (TEchnologies for MItigation of Space DEBRIS) project, to artificially open up earlier the structure, appears promising to enhance the global demisability of satellites. Indeed, exposing the internal components to the outside hypersonic flow earlier would enable an earlier temperature rise and thus enhance the burn up.
To get a better understanding of the early reentry phase (ranging from 120km to 100km), this study applies high-fidelity numerical methods to investigate the reentry behavior of the Eu:CROPIS satellite.
DSMC (Direct Simulation Monte Carlo) simulations are applied to the satellite Eu:CROPIS reentry and coupled with a structural FEM solver to investigate the aerothermal heating of the satellite during early reentry. A non-reactive three species mixture (O₂, N₂, O) flow is simulated assuming isothermal walls and diffuse reflection with full thermal accommodation. An aerothermal database, which serves as the input to the structural solver, is then built from the surface heat flux on 11 trajectory points ranging from 120km to 100km altitude. The coupling between flow and structure is achieved using Conffass framework (Coupled Numerical Fluid, Flightmechanics And Structure Simulations).
High fidelity FEM structural simulation, accounting for both outer and inner radiation, are performed, simulating the transient thermal response of the satellite along the reentry trajectory. Initial temperature of the whole satellite is set to -23°C at the starting altitude 120km.
Peak surface heat fluxes from the DSMC simulations reach up to 83 kW/m² at 100km altitude on the windward faces, driving the rapid heating of the outer structure while inner components remain shielded. The coupled flow-structure simulation shows that the inner components of the satellite are indeed shielded during the early stage of the reentry, thus delaying greatly the burn up of them. While the outer structure of the satellite quickly reaches melting temperature of the aluminum at 660°C after 1840s at 115km altitude, the inner components remain comparatively cold like the inner payload which temperature does not excide 80°C.
These findings highlight the importance of accounting for structural shielding in reentry risk assessments. They also enable the setting up of a demise strategy by placing the demisable joints, which are thermosensible, at strategic locations to maximize the break-up altitude.