Re: Hybrid engines
That solution requires 2 different types of engines, which means more spacecraft mass dedicated to engine. Maybe not a bad tradeoff ans maybe it is.
I do not see why the practical aspects of VASIMR (microwaves heating a plasma) are that hard to prove. We've been manipulationg microwaves for decades. Heating plasmas too. It "works in the lab" so I say build and flight test in LEO test a solar powered proof of concept vehicle.