In Alien, it is never stated why a commercial towing vehicle such as the Nostromo would need a self destruct mechanism. However, several theories have been proposed by fans in the years since: * In an emergency, it would be better to blow up an out-of-control starship hauling a colossal ore refinery rather than allow it to crash into a populated planet or colony. * Contemporary space rockets include self destruct systems in case they veer off course at launch, and the system on the Nostromo could be of similar purpose (although it seems likely that the Nostromo was built in orbit rather than launched from Earth). * The presence of Colonial Marines in the Alien universe implies there must be a threat or threats that the Marines were established to counter. Therefore, self destruct