Beamed Energy Propulsion (BEP) is a rocket science, but you don’t have to be a rocket scientist to grasp the concept. Because it is simple as any ingenious ideas are. In the next four paragraphs and in simple layman terms I will explain it to you.
It is all about rockets. What everyone knows about them? On Earth motion is based on pushing from the medium, wherever the motion takes places: cars pushing from pavement by wheels, swimmers pushing from water by limbs, etc. Rockets fly in space and space is mostly a vacuum, it is empty. Rockets move in space using reactive principle, i.e. exhausting hot gases (backward) and pushing away from exhaust in opposite direction (forward). Rockets have to carry all their fuel and burning agent on board, because there is nothing in space that can be used for burning fuel (like air for burning gasoline in automobiles on earth).
Rockets cargo space is very expensive. Why? Because with so many elements on board: fuel, oxidizer, cryogenics, tanks, lines, you name it, there is a small (and very expensive room) for the payload. If we could only find a way to separate the heavy energy source from the rocket, the gain in efficiency of such rocket will be tremendous.
This can be done if instead of carrying energy source on board, we will beam that energy from a remote power station. What kind of beam it can be? Laser beam, microwave beam, even x-ray, in all cases energy will be delivered to the rocket with speed of light. When a great number of photons is focused (even loosely) on a solid matter, such matter is evaporated and ionized almost instantaneously, i.e. the release of energy is much higher than one used from burning hydrogen. So, laser-driven vehicle will be still flying on the same rocket principle (pushing away from its exhaust), but exhaust energy and structural lightness will be incomparably superior to hydrogen-burning rockets.
Beam-driven rocket is equipped with beam- collecting optics (i.e. mirrors) and some relatively lightweight solid fuel. That is it: no more tanks, oxidizer, cryogenics, nozzles, lines, – the rest will be cargo. Such rocket will be a subject of 4P Principle, formulated by the founder of laser propulsion, Arthur Kantrowitz: Payload, Propellants and Photons, Period!
How much beamed energy is more efficient than traditional hydrogen burning? About hundred times! Currently, for reasons disclosed above we are paying $10,000 per pound of payload delivered from ground to low earth orbit only. If space launches will be done with high-power lasers, the price per pound of payload will fall to $100! This is 100-fold gain!
In addition to laser beams, other types of energy transfers using microwave, x-ray and even particle beams are getting explored for BEP. The number of in-lab demonstrations of BEP principles grows every year, and the day when we will achieve in-space BEP demonstration becomes inevitable. Of course, there are still a plenty of scientific and engineering problems which should be solved before BEP will bring us its benefits. However, the days for first practical use of beamed-energy propulsion are near.