On the Existence of Space War Tactics…
February 22, 2010 1 Comment
There are two great factors in space warfare that will set it off sharply from anything else in human experience, and those two factors will modify fighting ship types, strategy and tactics profoundly. They are:
(a) the extent of space. and (b) the tremendous speed of the vessels…
Speeds in space are as stupendous as the spaces they traverse. Needing seven miles per second to escape the Earth and another twenty to make any reasonable progress between the planets, even the slowest vessels will have speeds of twenty-five miles per second. Warships, presumably, according to type, will have correspondingly higher speeds—perhaps as high as fifty miles per second for the faster scouts.
When we talk of gunfire or any other means of offense, we have to hear these dizzy speeds firmly in mind. The conclusion is irresistible that scouting, tracking, range finding and relative bearings will all be observed otherwise than visually…
…Each of the combatants must compute the other’s course from blind bearings and ranges and lay their guns or point their torpedo tubes by means of a differential calculator.
However, in this blind tracking there is one peculiarity of these ships that while it is in one sense a source of danger to them, is of distinct assistance. In the fleeting minutes of their contact, neither can appreciably alter course or speed! This is a point that writers of fiction frequently ignore for the sake of vivid action, but nevertheless it is an unavoidable characteristic of the ether-borne ship.
The human body can withstand only so much acceleration and the momentum these vessels carry has been built up, hour after hour, by piling increment of speed on top of what had been attained before. In space there is no resistance. Once the rockets are cut, the ship will soar on forever at what ever velocity she had at the moment of cutting. Her master may flip her end over end and reverse his acceleration, but his slowing will be as tedious and cautious as his working up to speed. Jets flung out at right angles merely add another slight component to the velocity, checking nothing.
Rocket experts have stated that an acceleration of one hundred feet per second per second can be withstood by a human being—perhaps one hundred and fifty in an emergency. The master of a vessel proceeding at forty miles per second applying such an acceleration at right angles would succeed in deflecting his flight about one hundred miles by the end of the first minute, during which he will have run twenty-four hundred—a negligible turn, if under fire. Applied as a direct brake, that hundred miles of decreased velocity would slow him by one twenty-fourth—obviously not worth the doing if the emergency is imminent.
WITH these conditions in mind, let us imagine a light cruiser of the future bowling along at forty miles per second on the trail of an enemy. The enemy is also a cruiser, one that has slipped through our screen and is approaching the earth for a fast raid on our cities. He is already decelerating for his prospective descent and is thought to be about one hundred and fifty thousand miles ahead, proceeding at about thirty-five miles per second. Our cruiser is closing on him from a little on his port quarter, and trying to pick him up with its direction finders.
So far we have not “seen” him. We only know from enciphered code messages received several days ago from our scouting force, now fifty millions astern of us, that he is up ahead. It would take too long here to explain how the scouts secured the information they sent us. The huge system of expanding spirals along which successive patrols searched the half billion cubic miles of dangerous space lying between us and the enemy planet is much too intricate for brief description. It is sufficient for our purposes that the scouts did detect the passage of the hostile cruiser through their web and that they kept their instruments trained on him long enough to identify his trajectory. Being neither in a position to attack advantageously nor well enough armed—for their function is the securing of information, and that only—they passed the enemy’s coordinates along to us. This information is vital to us, for without it the probability of contact in the void is so remote as to he nonexistent.
The ship in which we are rushing to battle is not a large one. She is a bare hundred meters in length, but highly powered. Her multiple rocket tubes, now cold and dead, are grouped in the stern. We have no desire for more speed, having all that is manageable already, for after the few seconds of our coming brush with the enemy our velocity is such that we will far overrun him and his destination as well, it will require days of maximum deceleration for us to check our flight and be in a position to return to base.
Our ship’s armament, judged by today’s standards, will at first sight appear strangely inadequate. Our most destructive weapon is the “mine,” a simple sphere of meteoric iron about the size of a billiard ball, containing no explosive and not fused. The effectiveness of such mines depends upon the speed with which they are struck by the target ship—no explosive could add much to the damage done by a small lump if iron striking at upward of thirty miles a second. Then there will be torpedo tubes amidships. and perhaps a few guns. but it may be well to post pone a discussion of the armament until we have examined the conditions at the place of battle.
Although we know in a general way where the enemy is and where he is going, before we close with him we must determine his course and speed very accurately, for our ability to hit him at all is going to depend upon extremely nice calculations. Our speeds are such that angular errors of so much as a second of arc will be fatal, and times must be computed to within hundredths of seconds.
This falls within the province of fire-control, a subject seldom if ever mentioned by fiction writers. There is no blame to be attached to them for that, for the problems of fire-control are essentially those of pure mathematics, and mathematics is notoriously unthrilling to the majority of readers. Yet hitting with guns—or even arrows, though the archer solves his difficulties by intuition—requires the solution of intricate problems involving the future positions and movements of at least two bodies, and nothing more elementary than the differential calculus will do the trick. In these problems interior ballistics, for all its interesting physics, boils down to a single figure—the initial velocity of the projectile, while exterior ballistics evaporates for the most part the moment we propel our missile into a gravityless vacuum. In space we are to be concerned with the swiftly changing relationship of two rapidly moving vessels and the interchange of equally swift projectiles between them, the tracks of all of them being complicated curves and not necessarily lying in a plane.
In its simplest statement the problem of long-range gunnery is this: where will the enemy be when my salvo gets there? For we must remember that even in today’s battles the time the projectile spends en-route to its target is appreciable—fully a minute on occasion, at sea, during which the warship fired upon may move as much as half a mile. Under such circumstances the gunner does not fire directly at his target, but at the place it is going to be. That requires very accurate knowledge of where the enemy is headed and how fast he is moving.
At sea that is done by observing successive bearings and ranges and plotting them as polar co-ordinates, bearing in mind that the origin is continuously shifting due to the ship’s own motion. This work of tracking—the subsequent range-keeping and prediction of future ranges and bearings—is, done in our times in the plotting room. This is the most vital spot in the ship, for if her weapons may be likened to fists and her motive power to legs, her optical and acoustical instruments to eyes and ears. then the plotting room is the counterpart of the brain. There all the information is received, corrected, digested, and distributed throughout the ship. Without that co-ordination and direction the ship would be as helpless as an idiot.
Well, hardly that helpless today. Our individual units, such as turret crews, can struggle on alone, after a fashion. But not so with the ship of the future. There the plotting room is everything, and when it is put out of commission, the ship is blind and paralyzed. It will, of course, be located within the center of the ship, surrounded by an armored shell of its own, and in there will also be the ship control stations.
THE BEST WAY to approach the problems our descendants will have to face is to consider a simple problem in tracking that our own warships deal with daily. It is an absurdly simple one compared to the warped spirals to be handled in space warfare, but it will serve to illustrate the principle. In Fig. 1. it is shown graphically, but in actual practice the elements of the problem are set up on a motor-driven machine which thereupon continuously and correctly delivers the solutions of problems that would take an Einstein minutes to state. As the situation outside changes, corrections are cranked into the machine, which instantly and uncomplainingly alters its calculations.
In the figure we have the tracks of two ships, ours the left-hand one. For the sake of clarity and emphasis I have made the ratio of speeds three to one, hut the same trends would be shown at the more usual ratio of, say, 20:19.
At positions “1,” “2,” “3” and so on, we observe the range and bearing of the target, and plot them. By noting the differences between successive readings and the second differences between those, we soon have an idea of the type of curve the rates of changes would plot into. In a short time we can also note that the rates themselves are changing at a certain rate. This is a rough sort of differentiation—by inspection—and to one familiar with such curves these trends have a definite meaning.
For example, it is apparent that the series of observed angles “Beta” are steadily opening, signifying that we are drawing past the target. Any sudden alteration of the second differences, such as occurs at “8,” at once indicates a change of condition on the part of the enemy. He has either turned sharply away or slowed to half speed, for the bearing suddenly opens nearly two degrees more than the predicted bearing. We learn which by consulting our ranges. It could be a combination of changed course and changed speed.
The ranges during the first seven time-intervals have been steadily decreasing, although the rate of decrease has been slowing up, indicating we are approaching the minimum range. At “8,” though, the range not only fails to decrease, but the rate of change actually changes sign. We know without doubt that the enemy has turned away.
The importance of having the machine grind out predicted bearings and ranges, aside from the desirability of speed and accuracy, is that at any moment smoke, a rain squall, or intervening ships may obscure the target. In that event the gunners need never know the difference—their range and bearing indicators are ticking away like taximeters, fed figures by the controlling range-keeper. It would not have mattered if sight had been lost of the enemy at “4”; the gun fire would have been just as accurate up to the time he changed course as if they had the target in plain sight.
As a matter of fact, the guns are not pointed at the target at all, but in advance of it, as is shown in Fig. 1 (a), both range and bearing being altered to allow for the forward movements of the target while the shells are in the air. The projectiles may be regarded as moving objects launched on a “collision course” with regard to the enemy vessel.
Speaking of collision courses, it is an interesting property of relative bearings that when the bearing remains constant—except in the special case of the vessels being on parallel courses at identical speeds—the vessels will eventually collide, regardless of what their actual courses and speeds are. Hence, from the time the shots of the salvo left their guns—Fig. 1 (a)—until they struck their target, the target bore a constant angle of thirteen degrees to the right of the nose of the shells. (This knowledge has some utility in estimating the penetration of armor at the destination.)
In the example above, all the movement can be regarded as taking place in a plane; the ships follow straight courses and they maintain constant speeds. Our terrestrial problems are in practice much complicated by zigzagging, slowing down and speeding up, but at that they are relatively child’s play compared to what the sky-warrior of the future must contend with.