Why does a spacecraft propulsion system either have high thrust or high specific impulse, but can’t have both at the same time?

Question

I just started learning about space travel. I’ve heard that a spacecraft propulsion system either has high thrust + low specific impulse, or low thrust + high specific impulse.

As far as I know, high thrust means a propulsion system has high mass flow rate, achieving higher acceleration.

High specific impulse means a propulsion system can generate more thrust for given amount of propellant used, achieving higher fuel efficiency.

So if a propulsion system such as ion thruster has higher specific impulse than chemical rocket, why can’t engineers increase the output of ion thruster to increase thrust, achieving both high fuel efficiency and high acceleration to replace chemical rocket?

In: Engineering

Answer 1

I guess your description is right. The problem is chemical rockets and ion thrusters are completely different propulsions systems. Except both shoot things out the back which is without alternative as of now.
You could achieve more of what you want but it would require much more weight for the propulsion system meaning no carry capacity.