Can we have our cake and eat it too? Can we have a non-thermal nuclear propulsion minimizing waste heat?
* Yes. By making the fuel into dust.
There is the original dusty fission fragment version. These systems can have ISP of 500,000 to 1.5 million. However multi-gigawatt systems would have only a few dozen newtons of thrust. The systems could potentially reach 5% of the speed of light.
Increasing thrust by 10 times at the expense of a reduction by a factor of 10 in specific impulse brings about an interesting tradeoff between the mission duration and the propellant expended. An ?afterburne, the physical implementation of this thrust increase, injects an inert gas into the FFRE exhaust beam. This concept is proposed for a future NIAC study.