"Now the other limit," said Ishie. "This little piece of plastic will only stand a pressure approaching the point at which it begins to distort and run out of the field. This stuff is quoted to have a compression-yield strength of one hundred ten pounds to the square inch. We probably shouldn't exceed ... hm-m-m ... ninety pounds. Let's get the Cow to tell us how big a chunk of surface area that represents."
The answer was discouraging. Mike rapidly converted the figure in centimeters to feet, and came up with nearly an eighty-three foot diameter for a circular surface.
"Looks like we'll have to put it out on the spokes," he muttered in disgust, but Ishie shook his head quickly.
"No need, Mike. Later on we'll need a few thrust points out on the rim for good aiming, but we don't have to have all this surface area in one unit or even in one place. Also, we do not need to consider only the surface of an homogeneous piece of plastic material.
"This plastic can be cast. Very easily. In it, we can insert structures that will absorb the strain from many surfaces within, rather than only on a front surface.
"I expect some of the glass thread with which the hull of the ship was made could be inserted with no trouble. Each thread, then, would take up the strain, and a mass of them distributed through the plastic could deliver a greatly increased amount of thrust from a volume of plastic rather than from a surface area."
Mike started to object. "To get an absolutely parallel magnetic field, the gap between the pole faces can't be very wide."
"Perhaps I wasn't considering pole faces," Ishie answered. "Our investigation has already shown that once initiated the thrust-effect works best in a very low magnetic field.
"Such a low, parallel magnetic field would quite probably be found inside of a simple solenoid coil."