The strange thing about the Jehad was that it could never have lifted off the earth under its own power. Although the twelve generators which would drive the Jehad to Mars produced fantastic voltage, their force would not have knocked down a child—in fact, the push from a single motor was about equal to the power exerted by a pigeon in flight.
However, it was the most efficient and most economical motor man could use to travel ninety million miles to Mars—which is not the shortest route, but the most practical since it makes use of the earth's motion and the sun's gravitational power.
The plasma motor, more correctly the traveling-wave plasma motor, was developed after several years of research at the NASA laboratories near Cleveland, expressly for space propulsion. The first big breakthroughs, which led to the eventual perfection of the machine, were made in 1961. Because the machine was so complicated, involving principles laymen found hard to understand, it had received very little publicity.
In the simplest terms, the plasma engine, like the rocket, makes use of Newton's law on the conservation of energy—for every action there is a corresponding and opposite reaction. But here the similarity with rockets ends.
In effect, it means that if you throw a ball, as much pressure and force is backward thrust on the hand as forward thrust on the ball. Since the ball has smaller mass, it sails through the air while your hand and body stay put because you are anchored by your weight and gravity. But in space you would go back in proportion to your mass, just as the ball goes forward. And if you continued to throw balls you would accelerate with each toss.
The plasma motor is an electric generator, "spread out." That is, the rotor—the part that revolves—is removed, the motor opened up and flattened. Then it is coiled into a tube so that the field travels at right angles to its normal direction. This makes the electrical field run down the tube in waves, instead of in a circular motion.
Instead of a rotor, some lightweight element is ionized—heated and vaporized until the electrons and protons of the atoms are torn apart—and the resulting plasma rides down the tube on the waves as circulating systems of positive (protons) and negative (electrons) charges. When they are expelled there is a good-sized kick—kinetic energy. In space, any kick, no matter how small, results in motion, which will continue unless another force is applied to stop it. But in this case the only applied force is more kicks forward, thus there is acceleration.
The chief advantage of the plasma motor is that it can give a very good thrust with a very small amount of fuel. Even the earliest calculations disclosed that the amount of fuel needed to accelerate and decelerate the ship amounted to practically nothing compared to the payload it could push through space. A one-hundred-pound thrust would suffice to drive a 150-ton spaceship to Mars. Compare this with the one thousand pounds of thrust necessary to lift one pound of payload by rocket from the surface of the earth.
The fuel used on the Jehad was lithium, the third-lightest element. It had been used in the first experiments with the plasma engine but, since it had to be heated to 2500 degrees in order to vaporize it, argon—which was a gas to begin with—was experimented with. However, it had been decided to use lithium, for two reasons: one, heat to vaporize it could easily be obtained through high frequency heaters powered by solar batteries; two, lithium is lighter than argon. Thus was gained double advantage.
In theory, the Jehad could travel five-ninth's the speed of light, or about one hundred thousand miles per second. As yet the Jehad had never attained this velocity, because building up to that speed would take months. In the 12-hour test flight, Spartan, Ludson and Gail Loring reported that the craft behaved according to expectations and there was reason to believe that, in practice, it would not fall short of its theoretical speed.