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. However, speed was not important, since a good part of the time on the trip would be spent in waiting for the earth and Mars to get into proper positions. It was necessary only to be fairly close to schedule in arriving on Mars. I had been trained in the operation of the plasma ship and to me it represented the summit of safety in space. That's why the trip to the Jehad seemed so long. I didn't feel secure in the Saturn capsule and I knew I'd be much safer on the Jehad.