CST: A new semi-empirical tool for simulating spacecraft collisions in orbit

This paper provides a general description of a new Collision Simulation Tool (CST) to model the consequences of orbital impacts involving large debris and satellites, with the aim to predict fragments distributions in case of sub-catastrophic and catastrophic impacts. The new tool is being developed in the framework of the ESA contract “Numerical simulations for spacecraft catastrophic disruption analysis”, carried out by the Center of Studies and Activities for Space CISAS “G. Colombo” of the University of Padova (prime contractor) and etamax space GmbH. The CST makes possible to model a large variety of collision scenarios involving complex systems, such as entire satellites with many design details included, and provides statistically accurate results with a computational effort orders of magnitude lower than hydrocodes. To this end, the simulation approach is based on a hybrid modelling strategy, in which every colliding object is described as a gross net of Macroscopic Elements (ME) representing spacecraft elementary building blocks. On one hand, individual fragmentation of Macroscopic Elements is addressed through the use of semi-empirical breakup models applied, at element level, only to those spacecraft parts which are involved in the collision. On the other hand, structural distortion, fracture, and separation of satellite broken parts are modelled with a discrete-element approach through the simulation of momentum transfer to Macroscopic Elements through the net, taking into account energy dissipation inside elements and across links. This paper provides a description of the CST simulation methodology and framework; preliminary results are also shown with respect to the tool validation process. Validation is done by comparing the tool predictions with empirical data from ground-based impact tests on simple targets (simple plates and Whipple Shields) as well as sub-scale spacecraft models. In the first case, the tool capability of predicting fragments distributions from plates and ballistic limit equations of shields is verified. In the second case, fragments distributions calculated by the software are compared with those derived from published experiments on a micro-satellite.