With the advances in tech since Cassini was built (late 80s tech really) I think an ideal follow up would be a pair of orbiters,  with similar capabilities to casssini (which presumably can be done for half or better the price as digital tech is halving in price and doubling in performance just about year on year) 2 orbiters,  one for Neptune and one for Uranus,  to complete the detailed study of the solar system. \n\nI'm not sure if they could be sent on the same rocket... Since the alignment that made voyager possible was a rarity, but I'm sure if it is (I. E travel together to Uranus,  then the Neptune bound probe leaves the Uranus probe before it makes it orbital insertion burn,  and use Uranus for a slingshot out to Neptune.... Which may require years and a few trips round the sun to raise its orbit to encounter Neptune.... \n\nIt's worth doing. Triton is a moon well worth looking at... And the source of Neptune's wind speeds is a question we would all like to see answered.. Not to mention the nature of Uranus and it's bizarre tilt.. \n\nThough I am of course pleased with Europa Clipper.... It's just such a shame exploration in space is always limited to one or two major missions..... When if any of us we're in charge,  we would have built several 'cassinis' (and possibly enjoyed some economy in scale) and sent them all over! \n\nSame goes for the curiosity Rover.   A marvel,  but why must it always be a unique and bespoke machine,  as if to maximize it's expense? Why could there not be a base Rover design,  make a number of them for landing in a number of places? \n\nFor example,  why is there not a base line space probe bus,  which can have bespoke instruments attached,  as target and mission requires? Much in the way Voyager/ Pioneer was done.... Their spacecraft busses were largely the same.... And look what they achieved. \n\nWould their not be savings in building another csssini but with 22St century equipment? \n\nI have never understood why beach mission requires a brand new and untested design EVERY time.