ORBITAL DEBRIS HAZARD FOR NUCLEAR ELECTRIC PROPULSION EARTH-ESCAPE TRAJECTORIES

Nuclear electric propulsion (NEP) is being considered for Moon and Mar s missions, both manned and unmanned. The low thrust to weight ratio o f NEP necessitates a spiral trajectory that very gradually expands in radius until Earth escape is achieved. Thus a NEP vehicle could well b e orbiting the Earth for an extended period-weeks or months- before es caping. This mission scenario implies that the probability of a collis ion with orbital debris may not be negligible. This paper describes a quantitative method for estimating the debris collision hazard for NEP vehicles. It is based on estimating, over extended time intervals, th e statistical distribution of the distances from the potential target to the nearest debris objects as a function of the target's trajectory and the spatial configuration of the debris population. The collision probabilities obtained for a NEP target passing through such a large spatial configuration of debris are then scaled for the projected grow th in the debris population, and for the larger population of untracke d, but still hazardous, debris. The specific results obtained indicate that the debris hazard may be significant for a large NEP vehicle in the 2015 era, particularly if its spiral trajectory is initialized bel ow an altitude of 1100 kilometers.