# Warp Speed, Scotty, but Easy on the Throttle

## ROBERT BURRUSS

April 16, 1991|By ROBERT BURRUSS

KENSINGTON. — When Captain Kirk orders Scotty to take the Enterprise to Warp 9, the cost of the ship's antimatter fuel is never mentioned.

Why?

Because the cost of even a simple starship maneuver is beyond comprehension -- but well worth consideration.

Assume that the starship Enterprise is as massive as two large supertankers -- i.e., a million tons. The fuel cost to get a million-ton ship to a speed of 1 percent of the speed of light works out to \$592 trillion. (The starship's engines are assumed to be 20 percent efficient -- i.e., 20 percent of the energy of the fuel gets converted to kinetic energy of the reaction mass. The exhaust velocity of the reaction mass is 2 percent of light speed. The reaction mass, water, is shot off into space at a rate of 200 kilograms per second. Energy cost is based on what we presently pay for electricity, 6 cents per kilowatt-hour.)

Compare that to the 2 tons of antimatter fuel that could -- were antimatter fuel available, which it isn't, yet -- supply all present human energy needs for one year.

That's why neither Kirk nor Scotty, nor the show's writers, mention fuel costs: the amounts are ridiculously large. Such energy costs would seem to preclude forever space travel on the scale suggested in the ''Star Trek'' series and in such movies as ''Star Wars'' and ''Aliens.''

Or do they?

To put these daunting energies into a perspective, consider that, at the current cost of electric energy (6 cents per kilowatt-hour), the solar energy striking the earth is worth \$3 billion per second! In one year, the value of the solar energy striking the earth adds up to nearly \$100 quadrillion dollars -- 25,000 times the U.S. national debt. Consider further that the earth intercepts only one part in two billion of the sun's radiant energy. The rest, to borrow a phrase from the science writer Nigel Calder, ''runs to waste in an endless desert of space.''

Another example: A spaceship the size of a Nimitz-class aircraft carrier (i.e., 100,000 tons) is cruising along at 1 percent of the speed of light. The captain orders a 90-degree course change. How much energy is needed to, in effect, go around a corner?

For that simple turn, the ship would consume nearly 15 times all the energy presently used by humanity in a year. The three-day maneuver would, at 6 cents per kilowatt-hour, cost \$82 trillion!

Eighty-two trillion dollars is pretty high for a simple right-hand turn. But some day -- in maybe a thousand years, or 5,000 years -- such costs might well be routine in human affairs.

In the last 2,000 years human energy demand has increased by '' nearly 10,000 times. (Five hundred times as many people, each using about 20 times as much energy.) But where might energy for large-scale space travel come from?

From the sun, of course. Remember that the solar energy striking the earth is worth \$100 quadrillion dollars per year -- and that that amount is less than a billionth of the sun's output? How might we possibly tap into such huge amounts of energy? Certainly we won't do it here on earth, there's simply not enough room; and antimatter, which is the preferred and ultimate energy storage method, will be far too dangerous to handle in a small setting like the earth's surface. We will have to collect the energy directly from the sun -- i.e., in space, near the sun!

It is not that the cost of space travel is going to be high. Rather, at this time in history, we are thinking small. The sun radiates enough energy in one second to supply our present needs for a million years. This, while we talk about energy conservation and fight wars over minute amounts of energy.

If we could harness a thousandth -- or a millionth, or even billionth -- of a percent of the sun's output, we would be able to accelerate million-ton spaceships as easily as do George ''Star Wars'' Lucas, Gene ''Star Trek'' Roddenberry, Ridley ''Alien'' Scott and James ''Aliens'' Cameron.

Human beings have the potential to do that. Someday we mighwell do it. But when we do, we will still be small compared to the sun.

Robert Burruss is a free lance.

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