Analysis of consequences of structural damage to the ISS Russian segment caused by collision with space debris

Under the conditions of increasing littering in the near-Earth space, a quantitative estimate of the criticality of consequences of the ISS penetration with fragments of space debris is a necessary tool when developing measures to recover from the contingency related to the penetration. The ISS Russian Segment (RS) is mostly susceptible to penetration due to the fact that it includes transportation spacecraft, which have weaker shielding as compared with the station modules. In connection with this, there arises a problem of determining the degree of criticality for penetration of the pressure hull of the modules, transportation spacecraft, propellant tanks and bottles in the RS taking into account possible types of catastrophic consequences of the penetration and the distribution of the penetration risk over the modules and the transportation spacecraft. In order to solve the problem, a procedure was developed for calculating the risks of a catastrophic penetration of the station, based on breaking up the original problem into two stages. Calculated during the first stage is the probability of penetration of individual compartments constituting the station and having a certain type of shielding protection, using a finite-element geometrical model of the station and a model of the technogenic environment. The obtained results are used during the second stage of calculation of the catastrophic penetration probability using statistic test method (Monte-Carlo method). This method uses a model of the ISS RS consisting of compartments with simplified shapes (cylinders and truncated cones), which makes it possible to simplify the procedure for obtaining a random penetration location and reduce the time needed to obtain statistically valid results. Based on the procedure presented in the paper, a program was developed, which is used for calculating the probability of catastrophic consequences of the ISS RS penetration. Analysis of calculation results has shown that the relative probability of a catastrophic penetration accompanied by the loss of the crew and/or the station is 13,3%; probability of emergency crew evacuation because of the threat of hypoxia is 3,716%; probability of emergency crew evacuation in a spacecraft with a punctured orbital module is 21,59%. The paper proposes steps that need to be taken in order to further reduce the risk of catastrophic consequences of the penetration through including into onboard systems the subsystem for promptly determining coordinates of the penetration location, as well as the use of oxygen masks by the crew during recovery operations.