Spacecraft Vulnerability To Space Debris Risk

The continuous growth of space debris population occurred in the last decade has caused serious threat to the space activity, which greatly affected the reliability and safety of the spacecraft in orbit. The traditional approach to space mission vulnerability with respect to micrometeoroids and orbital debris(MMOD) impacts, typically evaluates the probability of structural penetration. This approach, developed to deal with manned mission, is not well suited to evaluate satellite vulnerability: penetration of a satellite structural panel does not necessarily lead to the loss of the satellite or the loss of a component. The need for an improvement over the traditional way of computing the risk induced by MMOD to orbiting spacecrafts, from the early design phases to mission operations, strongly emerged.Based on the traditional approach to space mission vulnerability, this paper presents a developed methodology starting from the estimation of induced failures on spacecraft(S/C) components and from the computation of lethal impacts(with an energy leading to the loss of the satellite), and considering the equipment redundancies and interactions between components, the debris-induced S/C functional impairment is assessed.The developed vulnerability methodology uses the space debris data coming from the NASA ORDEM2000, and the finite element spacecraft geometric model establishing by the three-dimensional modeling software Patran as the inputs. The shielding analysis algorithm of spacecraft is developed to abtain the exposure area of the spacecraft and its components in the direction of the threat source. This methodology avoids overestimating the S/C vulnerability through the adoption of the Schafer Ryan Lambert(SRL) Ballistic Limit Equation(BLE) to evaluate failures on internal components. At last, the damage tree of spacecraft is established, and the failure probability of spacecraft is calculated by the method of minimum cut set to evaluate the safety and reliability of spacecraft in orbit.The analysis conducted on the three benchmark cases in Protection Manual, compared with the Bumper code, the maximum errors of the impact number was 4.69%, the maximum error of the failure number with the single protection structure and the whipple protection structure was less than 15% to verify the feasibility of the vulnerability analysis method. And three typical spacecraft components(electronic box, pressure tank and battery) are selected to analyze the their failure probability, and the relationship of the layout of the components inside the spacecraft and its failure probability. Finally, the analysis conducted on the case study satellite with 31 critical components shows the S/C vulnerability index to be in the range of about 0.2% over, with a significant reduction with respect to the results typically obtained with the traditional analysis, which considers as a failure a structural penetration of the satellite structural panels. And the result shows that additional local shielding to protect vulnerable components, relocation of components to less vulnerable areas and increase of the components distance from structural panels are the three measures to reduce the spacecraft vulnerability and the failure probability of components.