[Hunble]

F = MV^2

I fully understand why a low thrust (mass) and high specific impulse (high velocity) is important, since velocity is squared in the equation.

What had me confused is why lowering the velocity and increasing the mass (fuel expended) would be an advantage. It seems to me that you would always want the highest velocity possible.

This is what had me confused. Perhaps I am missing something important here, and that is why I was asking for your help.

[Frank_Discussion]

F=ma

With "a" being acceleration, which is not the same thing as velocity squared.

Momentum, however, is mass time velocity. Increase either or both of those quantities causes an increase in momentum. There is a an upper limit on exhaust speed, based on available power and other things, and that limit is reached before the limit on adding exhaust mass is reached. So throwing more mass is typically the more effective thing to do, though not neccessarily the most efficient.

Once again, kind of the best meatball answer I can give you. I'm a mechanical engineer, not a propulsions guy.