Thursday, January 15, 2009

Beamed Energy Propulsion: as a Field of Space Science

By Andrew V. Pakhomov

Beamed Energy Propulsion or, in brief, BEP, is a part of rocket science. However, you dont need to be a rocket scientist to get its idea, it is very simple, and I will explain it to you in the next several paragraphs.

The essence of rocket science is the principle of reactive motion. Cars on the highway are pushing pavement and move against it, swimmer pushes with his limbs (or fins) the water, and swims. Space has nothing to push from, because space is empty. So rocket pushes off its own exhaust formed by burning hydrogen with oxygen. Of course, since the space is a vacuum, everything (fuel, burner, tanks, cryogenics, combustion chamber) must be carried onboard.

With everything needed for reactive motion stuffed onboard, rockets have very little room for cargo, and this room gets very expensive. Literally, the major loads that rockets are carrying are their engines and fuel. If one could find a way to provide energy for rocket motion from outside, there will be no need to carry all that heavy parts: like oxidizer, cryogenics, tanks, lines, etc., and the gain in rocket efficiency will be enormous!

Energy can be delivered to the rocket from remote external source using light or, say, laser, x-ray, microwave high-power beams. With its mirrors, rocket will collect and focus that beams on its "fuel". Any solid matter can be a fuel. When high-power beam of photons is focused on a solid material, the material evaporates and ionizes instantaneously. The energy density in focused high-power beam exceeds hundreds to millions times one in the heat of burning hydrogen. Thus, beam-driven rocket will remain a rocket, it will be pushing from its own exhaust, but the energy of this exhaust is much higher, and the rocket itself is much lighter, comparing to hydrogen burners.

Payload, Propellant, Photons, Period! " 4P Principle introduced by Arthur Kantrowitz, the founder of modern laser propulsion, is an essence of BEP. Laser-driven rockets will consist of lightweight focusing optics (mirrors), modest amount of solid ablative propellant and the rest: the rest will be payload! No more fuel, cryogenics, tanks, oxygen, combustion chambers, etc.

Can efficiency of beam-driven rocket be compared to hydrogen burner? Yes, this can be done with scientific precision! For example, current price per lb. of a payload delivered to low earth orbit is $10,000. Calculations (repeated many time by independent researchers worldwide) show that with the laser propulsion space delivery price will be reduced to $100 per pound of a payload! It is a hundredfold profit!

The most developed today branch of BEP is called laser propulsion, it is based on energy transfer with high-power laser beams. The next in development is microwave propulsion, followed by barely explored BEP with x-rays and particles. The number of in-lab demonstrations of BEP grows every year, and the time of actual demonstration of beam-driven space rocket is getting closer. No question, there is still a lot of work ahead on development of BEP systems, but one thing is clear, they have a great future.

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