As French National Space Agency, CNES is in charge of monitoring safety requirements for people and property related to space operation as defined in French Space Operation Act (FSOA). To evaluate these requirements, and in particular to be able to assess the compliance with safety threshold, CNES has developed its own tools, DEBRISK and ELECTRA. DEBRISK software computes the ablation of the satellite and its components all along the reentry trajectory. This object-oriented code combines models for aerodynamic, aerothermodynamic and heat transfer. It supplies a list of surviving objects with their physical on-ground characteristics. This list is then used as an input for the ELECTRA software. ELECTRA software is designed to estimate human casualty risk during launch and controlled or uncontrolled re-entry. Using Monte-Carlo simulations, dispersion of various parameters as for example characteristics of surviving fragments and population grids, Electra computes the probability of incurring at least one victim on ground, the expected value of the number of victims and the impact risk per country. Among the four computation modes of Electra, the RF mode (final re-entry) is dedicated to the computation of risk a few hours or days before the un-controlled reentry of a space object.
One particular case of use of ELECTRA and DEBRISK occurred in 2018, when the Chinese space station Tiangon-1 re-entered the atmosphere and felt in the South Pacific Ocean on April 2nd. With 8,5 tons, this uncontrolled reentry was of large interest, nevertheless not concerned by the French Space Operation Act. In the frame of this high risk reentry, CNES made use of its flight dynamics technical expertise, the observation means activated through national and international cooperation and a variety of tools, both operational and expertise tools, as ELECTRA and DEBRISK, to predict the reentry date and location as well as the on-ground casualty risk evolution inferred by this high risk reentry.
First, this paper presents how the Tiangon-1 space station was modelled and how the ablation phenomena, induced by the atmospheric reentry, was computed using DEBRISK tool. Second, this paper deals with the risk computation using ELECTRA tool via its final reentry (RF) mode. The orbital parameters used as inputs for these tools were provided by OCC division in CNES who’s in charge of operational orbit determination and to operationally estimate the reentry point and date of reentries considered as high risk. The evolution of the orbit and the reentry prediction is presented in parallel with the evolution of the risk assessment.
This paper describes the prediction and risk estimation performed in CNES for the re-entry of the Chinese Space station Tiangon-1 in April 2018 using flight dynamics technical expertise, observation means and CNES tools, as DEBRISK (ablation computation) and ELECTRA (risk computation).