Sorry if I didn't do my homework

but there seems to be a lot of talk about various incarnations of photon propulsion in discussions about future space travel


But the way I see it, if you have a surface hit by a beam of radiation, which causes radiation pressure, and with it a force, which causes motion etc.
the total kinetic energy gained is just a tiny fraction of the energy that reached that surface.
In fact it is many orders of magnitude smaller.

So isn't that a waste of energy?

The way I see it it is far worse than any chemical propulsion we have today.

Am I missing something here?

Using light as a means of propulsion is better them chemically driven ones. Rockets can only ever achieve a certain speed which is not really that fast but using photons for example or ions as propulsion incredible speeds can be achieved.

Hmmm. Now, if you had a solar sail and headed toward the Sun, you could pick up the solar wind at some point. That has ions and electrons, as well as photons. Once you head outbound, you could have a photon-reactive surface that ablated when exposed to UV, for a little extra push.

But, all of that subsides at some point, say Jupiter.

I can not imagine using photon emission alone, straight out into space. Now, if there was something real about dark energy, maybe that could be beamed out instead...