I remember seeing a simple demonstrator some years back of a laser pulsing against the backside of a spinning disc, the geometry of things causing the heat from the laser to provide thrust.

I can't find the video I saw, but here's a general link on the topic:

https://en.wikipedia.org/wiki/Laser_propulsion#Laser_energiz...

This comes with many problems, but it does bypass the rocket equation, while not requiring Project Orion levels of trouble.