Instead of building a huge and slow prometheum hauler that is doing collecting and processing chunks at different times and thereby "idling" more than half of the time, isn't it worth building a very fast (>1k km/s) "small" ship that is optimised to run forth and back between the shattered planet and Nauvis, only stopping to drop science and take on biter egg? The prometheum belt storage is only there to cover for the travel time until the prometheum rich areas are reached.