But when she hit the outer fringes of the ionosphere—that upper layer of rarified protons, the rapidly moving current of high velocity ions known as the plasmasphere—she bucked like a kicked horse. From deep within her vitals, the throb began, a strumming, thrumming sound with a somewhat higher note imposed upon it, making a sound like that of a bass viol being plucked rapidly on its lowest string.
It was not the intensity of the ionosphere that cracked the drive of the Brainchild; it was the duration. The layer of ionization was too thick; the ship couldn’t make it through the layer fast enough, in spite of her high velocity.
A man can hold a red-hot bit of steel in his hand for a fraction of a second without even feeling it. But if he has to hold a hot baked potato for thirty seconds, he’s likely to get a bad burn.
So it was with the Brainchild. The passage through Earth’s ionosphere during take-off had been measured in fractions of a second. The Brainchild had reacted, but the exposure to the field had been too short to hurt her.
The ionosphere of Eisberg was much deeper and, although the intensity was less, the duration was much longer.
The drumming increased as she fell, a low-frequency, high-energy sine wave that shook the ship more violently than had the out-of-phase beat that had pummeled the ship shortly after her take-off.
Dr. Morris Fitzhugh, the roboticist, screamed imprecations into the intercom, but Captain Sir Henry Quill cut him off before anyone took notice and let the scientist rave into a dead pickup.
“How’s she coming?”
The voice came over the intercom to the Power Section, and Mike the Angel knew that the question was meant for him.
“She’ll make it, Captain,” he said. “She’ll make it. I designed this thing for a 500 per cent overload. She’ll make it.”