> This is only a problem for take off from large bodies. Yes, that's what we're talking about here. > Mass per mass, you'll get a lot more delta-v from a Hall

> This is only a problem for take off from large bodies. Yes, that's what we're talking about here. > Mass per mass, you'll get a lot more delta-v from a Hall engine than from a Merlin. Yes, that's what specific impulse measures (which is what most of the larger conversation has been about). As for bimodal propulsion, it makes you wonder if that would be worth doing at all, or if it wouldn't be better to just have separate engines and fuel tanks so each can do what it's best at. I suspect it might end up being less weight and complexity just to use an ion thruster as designed using xenon propellant. Xenon fuel tanks aren't typically all that big anyway.