By Jackie Wattles, CNN (CNN) — A half-billion-dollar rover that could be crucial to US lunar ambitions sits fully assembled but in a state of limbo, mere steps away from being ready for launch. Known as the Volatiles Investigating Polar Exploration Rover, or VIPER, the 948-pound (430-kilogram) vehicle is designed to scour the moon’s south pole to locate water ice: a key resource that, if found, could one day be converted to drinking water for as…