Assessing the motorized momentum exchange tether's operational lifetime: the multidimensional casualty area concept

This paper introduces the use of a multidimensional casualty area (MDAc) model for assessing the motorized momentum exchange tether (MMET) concept's operational lifetime and provides results of an example MMET casualty area computation. Because the MMET, a tether system with two, counter-rotating halves, is not stationary in the assumed inertial frame nor are its dimensions constant over its entire duty cycle, the simplifications and assumptions used to produce the currently accepted spacecraft lifetime equations prevent the equations from being easily applied to the MMET system. The multidimensional casualty area concept presented here provides a susceptibility-based casualty area that can be straightforwardly used in an analysis to assess the MMET concept's operational lifetime. Furthermore, the MDAc analysis offers both a mean estimate of the MMET concept's %-failure value and presents evidence that a diameter of a tether strand, whether configured as a multi-strand configuration or as a single-cored cable, is efficiently sized between the values of 0.8 cm and 1.0 cm.