Ben Bova: Moving around

Most of the vehicles we use for transportation carry their engines along with them. Automobiles, airplanes, ships, trucks, trains, even rockets all are powered by engines built into their bodies.

Gliders and sailboats don’t have engines. They draw their motive power from the sun-heated air: thermal updrafts and winds. Sleds and other downhill racers are propelled by gravity. But except for these few exceptions, our transportation vehicles are driven by engines that are integral to their design.

This means not only that the vehicle has to carry the weight of the engine, it must also carry the weight of the fuel that powers the engine.

This fact is especially limiting when it comes to flying machines: airplanes and spacecraft.

What if someone could design a vehicle that doesn’t need to carry all that weight? What if someone could design a vehicle whose primary power is outside the vehicle itself? It could cause a revolution in transportation technology.

Well, someone has. And he’s written a book about it.

“Lightcraft Flight Handbook” by Leik N. Myrabo and John S. Lewis (Apogee Books; 284 pages; $29.95) is a quirky but fascinating book about flying machines that are propelled by laser beams.

Leik Myrabo (his first name is pronounced “Lake”) has long been known in aviation circles as a daringly innovative designer of advanced concepts. He currently teaches doctoral candidates in engineering physics at Rensselaer Polytechnic Institute in New York.

John S. Lewis is professor emeritus of planetary sciences and co-director of the Space Engineering Research Center at the University of Arizona.

The “Handbook” that Myrabo and Lewis have written purports to be a declassified top-secret government document from the year 2020.

I have a special interest in the concept of propelling flying machines by laser beams. I worked at the laboratory where the first truly high-power laser was invented, in the early 1960s. One of the ideas we investigated back then was the concept of using lasers to propel spacecraft.

Rocket-propelled spacecraft are dreadfully inefficient. Their only real asset is that they can work in the vacuum of space, where all other known propulsion systems cannot.

But the amount of useful payload rocket launchers can carry is minuscule, compared to the launcher’s total weight.

The total takeoff weight of the fully-loaded space shuttle, for example, is roughly 1,500 tons. Most of this is propellant for the rocket engines. No more than 25 tons is payload: a mere 1.6 percent. The rest is structure, engines and propellant.

In contrast, my Toyota Camry’s curb weight is 3,263 pounds, and it can easily carry five 200-pound passengers, plus luggage. Thus, more than 25 percent of its total drive-away weight is useful payload, compared to the space shuttle’s 1.6.

You can see how inefficient rocket launchers are. Even the redoubtable Saturn V, which carried our astronauts to the moon, carried a useful payload of only 6 percent. The rest was mostly propellant.

The idea behind laser propulsion is to get rid of as much of the propellant and engine weight as possible. But how can you separate the vehicle’s main driver from the vehicle itself?

The laser is a device that delivers energy over distance. The idea we tinkered with in the 1960s was to use a laser as the motive force for lifting a spacecraft from the ground and propelling it into orbit.

Calculations showed that if we used hydrogen as the craft’s propellant and heated it with a sufficiently-powerful laser beam, we could design a spacecraft that needed much less propellant. It could be perhaps 50 percent payload. Even better than my Camry!

The laser beam would heat the hydrogen propellant to a much-higher temperature than it reaches when it’s burned in oxygen. Higher temperature means that the hydrogen leaves the rocket nozzle at a higher velocity. This, in turn, means more thrust per pound of propellant.

We tested the idea in a very small experiment and, sure enough, the laser beam pushed our toy model pretty much as we had expected.

To scale up our tabletop experiment to the point where a laser could launch real spacecraft, we would need a laser capable of at least a gigawatt output power. That’s a billion watts. Lasers haven’t reached that power output yet, although megawatt-class lasers do exist today.

Myrabo’s idea is to use laser beams to power machines that fly through the atmosphere — airplanes — as well as spacecraft. He envisions gigawatt-class lasers in orbit, where they derive their input power from electricity generated by solar-power satellites.

His “lightcraft,” as he calls them, would be capable of hovering in mid-air or flying at hypersonic speeds, Mach 10 or better. They could leave the atmosphere altogether and operate in space. They could accelerate so quickly that they would, to the human eye, simply seem to disappear.

So we have a round, disc-shaped flying vehicle that can hover, fly faster than the Air Force’s best fighter jets, disappear from sight altogether and go off into space. It would also glow in the dark, because of its high-energy propulsion system, and probably interfere with radio and other electronic signals.

Myrabo’s lightcraft sounds a lot like the classic descriptions of UFOs: flying saucers. Maybe his lightcraft actually exist! Maybe the ones that have been observed here and there weren’t designed on Earth!

And maybe, Myrabo and Lewis have figured out how to make such craft. Their book deals with the design of such vehicles. There are plenty of practical engineering problems to be overcome, including the “detail” of building solar-power satellites and gigawatt lasers to power the lightcraft.

But at least we know, in concept, how the extraterrestrials’ UFOs work.

Naples resident Ben Bova is the author of more than 120 books, including “The Return,” his latest futuristic novel. Bova’s Web site address is www.benbova.com

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