Terminal Run

Seventy milliseconds later a small grain can of highly volatile flammables was lit off from a spark generator, the grain can contained in a pocket of solid rocket fuel, a composite clay of complex chemicals that was surprisingly inert until it reached a high temperature, and then became alive with the winds of hell. The grain can exploded into incandescence, and the fuel in the pocket surrounding the can ignited and began to burn the neighboring fuel matrix, a volume of high-pressure combustion gases collecting near the pocket. The pocket was at the end of a long tunnel bored through the fuel assembly, the tunnel becoming wider near the nozzle of the missile farther aft. The combustion gas pressurized the tunnel until the aft part of the tunnel reached nearly the same pressure as the forward pocket, and the missile’s protective nozzle cover blew off into the sea. The missile nozzle began to channel the in creasing rush of exhaust gas, until the entire aft surface of the fuel was burning and nozzle-entry pressure had sailed up to tens of thousands of pounds per square inch. The rocket flames from the nozzle built up until the missile felt the acceleration. The force of the impulse from the fuel sailed beyond five g’s to twenty, and the missile’s speed increased from thirty knots to eighty. The missile body trembled violently as it passed through a region of natural frequency, the ride settling slightly, until suddenly the missile went supercavitating. The skin friction vanished to near zero when the water molecules at the surface of the missile vaporized to steam. The steam bubble grew from the sharp point of the nose cone seeker module all the way aft until it enveloped the missile’s nozzle, and soon the missile accelerated to 100 knots, 150, until it reached supercavitating terminal velocity at 308 knots.

The missile’s attitude was controlled by the nozzle, the rocket engine rotating to keep the thrust in line with the missile’s center of gravity, and adjusting for steam bubble shape variations. The control system was required to be one of the fastest processors on the planet for a silicon computer, since the time constant to control the missile had to be measured in the tenth of a millisecond. In one ten-thousandth of a second, the missile’s flight could degrade from perfection to disastrous, and only that rapid a response from the missile’s nozzle could keep it from tumbling.

The nose cone blue laser seeker came on in test mode, then illuminated the narrow cone of the sea ahead. The cone widened as the laser searched ahead in a spiral shape like a locomotive’s headlight. The laser saw multiple returns from the waves high above, but nothing yet from the target. The processor compared the sea ahead to its model of the sea from the target solution given it by the mother ship. It expected the target location to change with time, the target locus becoming a probability matrix, a circle of possibility that enclosed the target, and the circle grew at the maximum speed of the target, which had been assumed to be forty-five knots. The missile had been ordered to aim for the center of the probability circle, even though that had a minimal chance of being the location of the target. It was expected that as the missile transited the Target Probability Circle, the TPC, that it had at most a ten percent chance of detecting the target. The attack profile called for the missile to sail through the TPC and continue on for one TPC diameter and execute an Anderson turn, a loop in the sea that would put the missile on a reverse course on its exact transit line, except offset by five hundred yards to the west, and it would cruise through the TPC again, still seeking, and if that did not yield the target, it would turn again and reenter the TPC, this time another five hundred yards to the west. As this search continued, the weapon would chart a grid through TPC until the TPC was completely covered, even though the TPC grew bigger with each second, its boundaries expanding at forty-five knots. Eventually the target would be detected, and the missile would connect.

The weapons console lit up with the green light annunciator that the Tsunami was powered up, but there was a red light indicating that it lacked a target.

“Sonar, Captain,” Lien said into the intercom microphone, “do you have a contact to the south?”

“Captain, Sonar, no, sir. We’re blued out from the bearing of the torpedo launch to the torpedo.”

“Report the bearing of the beginning of the torpedo wake.”

“One seven five, sir.”

Lien dialed in a phantom target to the weapon control function of his command console.

“I’ve got a bearing line, Mr. First,” Captain Lien said, “but I need to decide whether to have the unit search and, if it fails to find a target, shut down and sink, or to send it out to search and on failure-to-acquire, execute a default detonation.”