Tuesday, January 6, 2009

Arthur Kantrowitz and Beginning of Laser Propulsion

By Andrew V. Pakhomov

On November 29, 2009, in New York City, in age of 95 passed away Arthur Kantrowitz. Kantrowitz will be always remembered among most prominent American scientists of past century as a founder of Avco Everett Research Labs, professor of Dartmouth College, holder of numerous patents (from medicine to space) and supporter of Science Court. However, in this short note I would like to say a few words about one of his greatest contributions, which he made for us all and for future generations: the founding of laser propulsion.

Laser Propulsion is a part of rocket science, but dont be discouraged by a silly tag: the idea is simple. We pay on average $10,000 per every pound of payload delivered to low earth orbit. Why that much? Because, we use very inefficient carriers: chemical rockets. These hydrogen gluttons have to carry everything onboard: fuel, oxidizer, cryogenics, tanks, lines, you name it, leaving a small (and very expensive room) for the payload. If we could only find a way to separate the energy source from the vehicle, deliver that energy to the vehicle from some power station, the gain in efficiency of such vehicle will be tremendous.

This can be done using energy transfer with laser beams! This idea was originally formulated in 1924 by Konstantin Tsiolkovsky, who believed that beams of light could serve as a source of external energy for driving space rockets, that removed the burden of fuel onboard and makes rocket much lighter, and hence, more efficient. Tsiolkovsky with his pioneering ideas forerun his time on at least 50 years, Kantrowitz who was 11 years old in 1924, made his pioneering contribution just in time.

In 1972 journal of Astronautics and Aeronautics was published with paper of Arthur Kantrowitz, titled Propulsion to Orbit by Ground Based Lasers. This paper started a new field of space science and technology: laser propulsion. Kantrowitz proposed a genius idea: to launch space satellites from ground to space using high-power lasers. When high power laser light is focused on a solid matter, such matter is evaporated and ionized almost instantaneously. The release of energy in such process, called laser ablation, is much more powerful than one used from burning hydrogen in rockets! Therefore, without changing the main principle of rocket propulsion (moving forward by pushing from exhaust), we can achieve much better and efficient way of launches, if our satellites will be just straddling the tips of powerful laser beams. Such systems will be much lighter and energy efficient, comparing to hydrogen-burning rockets.

Payload, Propellant, Photons, Period! " 4P Principle introduced by Kantrowitz was an essence of laser propulsion. Laser-driven vehicles 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, combustion chambers. As a result, scientifically-proven calculations have shown that the price of space delivery per pound will drop from $10,000 (hydrogen "burning rockets) to a modest $100 (laser-driven rockets): a hundredfold, revolutionary change in price!

The paper of Dr. Kantrowitz from 1972 marked the beginning of a new scientific quest. In early seventies Kantrowitz has initiated first research program on laser propulsion at Avco-Everett Research Labs, which for over a decade was the only research program in this field in the world. Later other projects ensued, first laser-propelled vehicles were launched (not into space yet, but high enough to prove the viability of an idea), other countries (Russia, Japan, Germany, China) and hundreds of scientists and engineers joined the quest for laser propulsion (and other forms of beamed-energy propulsion, such as microwave propulsion). However, we should always remember one man who started it all: Arthur Kantrowitz, the father of laser propulsion.

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