In recent years, the development of active removal missions, to face the\udgrowing risk of catastrophic collisions and new debris generation due to the high\uddensity of orbital debris in LEO, is widely discussed in the international space\udcommunity. Besides legal and political issues, active removal solutions are strongly\udhampered by the high costs involved. Chemical propulsion might represent the\udpreferred way to carry out the controlled reentry of large abandoned objects, and, in\udthe perspective of cost reduction, hybrid rocket technology is considered a valuable\udoption, due to the potential lower fabrication and operational costs, if compared with\udbipropellant liquid systems. The possibility to use nontoxic propellants, besides\udtheir lower prices, reduces the complexity of handling, storability, and loading\udoperations, decreasing the connected costs and avoiding the need of a special staff.\udSolid rocket technology allows for very small and compact motor units, although\udwithout throttleability and reignition capability and characterized by lower safety\udlevel than liquid and hybrid systems. This study deals with the preliminary design\udand mass budget of solid, liquid, and hybrid propulsion modules, as well as their\udcomparison, to be used for active removal of large abandoned rockets in LEO.
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