Considering that a lot of well respected coaches suggest lunges as both warmup and strength work, I would hazard a guess that if lunges made your knees useless you may have been doing them incorrectly. Under striding and overextending the knee past the toes is a very common mistake I see that could definitely result…

This. I came here to write almost exactly this. Current real world ion engines are designed with the specific purpose in mind of keeping overall weight low as well as generating thrust and providing fuel over long periods. It would seem that if you’re willing to accept the higher weight and the fact that you’ll need…