The Family Tree of the missiles. Probably the first type of all was the catapault-launched (ye stronge right armme) followed by the gravity-powered (or cliff-borne) bomb.]

Concerning the Missile Family, its ramifications—and why rocket weapons behave—or misbehave—as they do.


Most observers of military mat­ters, in uniform and out, seem to be united in the conviction that the position of the gun as the one and only reliable military long-range weapon seriously threatened. The indications that this is the case cer­tainly are easily visible—bombard­ment rockets are crowding the field guns, long-range rockets have far surpassed any guns and are even crowding the bombing plane, and missiles, of all kinds and types, are crowding everything else. If it were possible to poll the weapon experts, it is quite likely that a majority of them would be moved to prophesy that the gun is going to be fully and completely replaced by the missile within two decades at most, probably less.

Of course there is a difference between listening to such statements and analyzing them. Prophecy is a hazardous business and one can never be too sure about such things, technological developments have taken queer and unsuspected turns in the past and will do so again.

There have been threats to the position of the gun before and es­pecially on two occasions these threats looked serious, at least to some contemporaries. But in both cases the outcome was that the threats vanished, not the guns. It is interesting that these threats were, in one case, rockets, and in the other missiles. The rocket threat is now known to military historians as the Congreve Period which lasted from about 1804 to about 1850. During that time Congreve bombardment rockets outranged and "outeconomized" the contemporary guns. But then the guns acquired rifling and later recoil absorbers and cartridges—and the crude blackpowder rock­ets of Congreve and his successors vanished.

The other threat concerned not guns in general but only their most impressive variety, coast defense and naval rifles. When, after a long period of elementary mistakes and of trial and error the naval torpedo emerged as an effective weapon, it was prophesied that torpedo tubes would take the place of harbor batteries and that the floating coun­terpart of the coast defense battery, the turret guns, would likewise be replaced. But everybody knows that even during World War II—not counting submarine warfare—the big naval rifles, with radar's as­sistance, caused more damage than torpedoes.

In the light of these past events one might be inclined to feel that today's discussions are rather futile and that anv attempt at prediction is useless. But, in spite of the oft-quoted saying, history does not re­peat itself. It may seem to do so superficiallv, but there is no actual repetition, merely a recurrence of similar patterns. And when a fundamental factor changes, and en­tirely new set of conditions is created automatically. There are even two fundamentally new factors now, both acting in the same direction. Up to a few years ago the accuracy of a weapon was the prime criterion in judging its effectiveness. If accuracy was lacking, either inherently or through circumstances, volume of fire could often serve as a substitute, produc­ing, of course, the difficulties of volume supply.

But the two new factors, the proximity fuse and the atomic bomb, abolish the requirement of accuracy without the need for multiplied volume. The proximity fuse con­verts any reasonable near miss into a hit and the inexpressible violence of an atomic explosion works in the same direction. Even ten tons of TNT are wanted in a half mile miss—but the trn or so pounds of plutonium which constitute "critical mass" are as destructive and deadly half a mile awav as they are directly overhead.

This fact changes history in general—and the theory of weapon design is merely a small part of history which is changed along with the rest. The potential future of the missile is caused not by its own existence, but by the existence of the fission bomb.

Uefore we go on it is necessary, however, to clarify the meaning of the terms which are going to be used. The dictionary defines the word 'missile' as "a weapon or thing thrown, or designed to he thrown, to injure another.' Strictly speaking the term missile embraces the whole list, coconuts and boom­erangs, arrows and crossbow darts, pistol and rifle bullets, mortar pro­jectiles and sixteen-inch shells, hand grenades and airplane bombs, ba­zooka rockets and V-2s. But in military parlance missile has come to mean something else, although it is not easy to state in a few words just what it does mean.

Somewhere in classical literature—I forget just where—there are two lines reading: "Canst thou stop the floods of the river? Or canst thou call back the arrow shot from the bow?" Well, a missile, in contemporary military English, is the arrow that can be called back after it has been shot, or that can at least be deflected to hit another target than the one against. which it was first discharged. Hence the word missile, as now used, does not include projectiles fired from a gun or simple solid fuel rockets fired from a launching tube.

Even with this restriction the "family tree" of missiles is a growth bearing diversified fruit. There is one branch which is that of the gravity-powered missiles, otherwise known as airplane bombs. The majority of them are as much be­yond the influence of the bombardier when released as artillery shells are beyond the influence of the gunnery officer after the lanyard has been pulled. But some are guided, by means of movable tail fins—as in the Azon bomb—or a movable shroud wing—as in the Roc—the fall of the bomb can be deflected so that it may hit a target which an ordinary bomb of the same size, weight and shape would miss.

All the other branches of the missile family have it in common that they are both powered in one way or another and guided in some manner, even if the guiding is some­thing as simple as a robot pilot capable only of keeping them on a straight course. While missiles may be classified according to the system of guiding used, the picture becomes much clearer if classification is made according to power plants. For, after all, it is the power plant which determines the essentials of per­formance, not the method of guid­ing.

Going by power plants we get two large groups, the engine-powered missiles and the rocket-powered missiles. In order to start with the less interesting kind so as to pro­gress to the more interesting varie­ties we'll begin with the engine-powered missiles.

Among them there is one branch which is isolated and comparatively old. It is the naval torpedo, engine- powered like its more recent winged relatives, but designed for a specific element—for water. All others have the air as their element and most of them rely on the air as a carrying medium, they are aerodynamically supported when on their mission.

Just as the naval torpedo can best be defined by stating that it is an unmanned model submarine, the aerodynamically supported engine-propelled missiles are pilotless model airplanes. The word "model" has been inserted to indicate that they are usually too small to be man-carrying, but that is not a hard and fast rule. The first of the missiles which saw extensive operational use, the German V-l flying bomb, was large enough to be man-carry­ing. Indeed, there existed a piloted "suicide version" of the V-l which was not used because of the lack of volunteers.

That the V-l used the so-called impulse duct or reso jet was merely a result of cheapness of manufac­ture and ease of mass production of this particular kind of jet engine. Theoretically a missile of the engine-powered aerodynamically supported group can use any kind of engine, reso jet, turbo jet, athodyd—ram jet or Lorin Duct—and even an or­dinary aircraft engine with propel­ler. Those that are simplest in de­sign, reso jet and athodyd, happen to have the disadvantage of being in­capable of functioning when at rest, they need a launching device or a rocket booster for take-off.

The tactical uses of the engine-powered missiles are obvious. They can serve as a substitute for long-range artillery—like V-l—they can serve as Air-to-Ship and Air-to-Ground weapons, or even, if athodyd-powered and provided with rocket booster, as Ground-to-Air weapons. They all share the draw­backs of not being able to travel at very high altitudes—hardly more than 50,000 feet—and they are all vulnerable to interception, both by interceptor planes and by antiair­craft fire. There can be little doubt that a manned interceptor plane will always be superior in performance to any interceptible missile of that kind; the engine in a piloted plane which is expected to return to its base after performing its mission can and always will be more highly refined—and more expensive—than the engine installed in a missile which can be used onlv once.

It is interesting that much of the interception from the ground will always be done by antiaircraft guns. The limit is at about two miles from the ground. Even a high-accelera­tion antiaircraft missile will not climb to a two-mile altitude faster than an ordinary antiaircraft shell. Expressed in terms of the time in­volved, the limit is in the neighbor­hood of ten seconds, which cor­responds to about two miles. If the missile to be intercepted is higher than two miles, or farther away than ten seconds of shell flight, antiair­craft missiles have an inherent su­periority. Below those limits the superiority is with the guns.

This brings us to the group of antiaircraft missiles which at the present moment is almost synony­mous with missiles which, like the preceding group, are aerodynamicallv supported but rocket powered. All known examples happen to be German. They were Junker's Schmelterling—Butterfly—which had been designated as V-3 by the Nazi Ministry of Propaganda, Rheinmetall's Rheintochter—Rhine-maiden—and the antiaircraft rocket Wasserfall—Waterfall. Sclimetlerling looked like a small airplane, the fuselage was filled with electronic equipment and a small generator, driven by an impeller sticking out in front. It had two rocket units, above and below the fuselage, which were jettisoned when exhausted. Rhein­tochter was a six-winged rocket with the rocket jets emerging slantwise from the spaces between the wings, with four stabilizing fins around the nose, with a "warhead" carried in the tail section and a four-winged booster rocket. Wasserfall was a small edition of a V-2 rocket, pow­ered not by liquid oxygen and alco­hol like V-2, but by nitric acid and Visol A—Vinyl ethyl ether—and equipped with the proximity fuse Kugelblits—ball lightning. All these antiaircraft missiles were guided from the ground. All came too late to take any active part in the war, but they represent prototypes of ground-to-air weapons to come.

A-4b has to be added to the group of rocket powered and aerodynamically supported missiles. Like its half-size offspring Wasserfall it had four stubby swept-back wings in addition to its four large stabiliz­ing fins. But in the case of A-4b the purpose was somewhat differ­ent, like the original A-4 or V-2, the A-4b was to be used as long-range artillery, the wings were to add a hundred mile glide to the ordinary 200 mile range of the A-4.

Of course the inaccuracy result­ing from such a glide path is apt to be so great that even an atomic war­head could not make up for it. Guid­ing by radar from the place of firing also will not work at such ranges any more, radar operates along a line of sight much like optical seeing, and at 300 miles the rocket would be below the horizon and out of reach for radar. Besides the rocket is not as ultra-fast along the glide path as a true long-distance rocket, hence the virtually noninterceptible long-dis­tance rocket becomes interceptible during the last sixty or seventy miles, hardly an improvement.

[This is not a complete list of German rocket weapons which were under development. Those mentioned are representative examples, but there existed other types, like Enzian— Gentian—Grosser Enzian—Big E—Frits (X-4) and others]

The last group of missiles, the group which is the most interesting from the scientific point of view and also of greatest potential value for peaceful as well as for military pur­poses is the group of rocket-pro­pelled and aerodynamically un­supported missiles. Hence these missiles are not limited in altitude either by their power plant or by winglike attachments which rarely help much in any case but which al­ways successfully impede a rocket's performance. Theoretically the aerodynamically unsupported rock­ets can attain any size, any altitude, any range and any speed. And they are virtually noninterceptible. In­terception by similar missiles is not quite impossible but will take some doing—but even those who believe that they might be interceptible admit that there cannot be a hundred per cent interception—and the atomic warhead of the one which was not intercepted naturally accounts for a city.

The last group, at the instant of writing, comprises just two known types, the German A-4—V-2— rocket and the American GAP A—Ground-to-Air-Pilotless-Aircraft—designed as a prototype of missiles meant to intercept A-4 missiles.

We'll try to see now what such long-range missiles can do and in order to have a comparison of some kind, hypothetical long-range guns will be used for this purpose step by step. There is, of course, an upper limit for the performance of long-range guns and this limit seems to have been approached rather closely. But there is no upper limit to the size of long-range rocket, even though the larger sizes could not be built at the present moment.

The problem of rocket ranges, like that of gun ranges, is one of the problems of the science of external ballistics. It is called external, be­cause it shows not the slightest bit of interest to the things that happen to a projectile inside the gun barrel, or, in the case of the rocket, to what happens inside the rocket motor. External ballistics begins at the gun muzzle. And the only things which the expert in this field wants to know about the gun are the velocity with which the shell leaves the muzzle and the direction of the axis of the gun barrel. What he really means by that is the angle formed by the axis of the barrel with a line from the gun barrel's breech to the cen­ter of the Earth. This angle, minus 90° is what is called the elevation of the gun. Only when details have to be investigated is he also interested in the "real elevation" of the gun, its height above sea level. Again this is not what he really wants to know, he is out for the air density at the muzzle.

Diagram II: One possible orbit for a 7000 mile trajectory of a rocket. It goes more than 7000 miles up to make the ground distance.

In some ways the science of ex­ternal ballistics is rather simple, in others it is easily the most compli­cated and most difficult science in nature or rather in man's mutual re­lationships. Not only for simplicity's sake but because a magazine has only so many pages I'll try to stay on the simple side. And I'll state at the outset without wasting time and space for proof, that a gun has theo­retically maximum range when the elevation is 45°.

Forgetting about a few factors at first—but I do like to mention what those neglected factors are. They are:

(1) air resistance,

(2) the fact that the surface of the Earth is not a plane but a sphere or something very close to a sphere,

(3) the fact of the Earth's diur­nal rotation,

( 4) the fact that the line to the center of the Earth at the point of firing is not parallel to the line to the center of the Earth at the point of im­pact, and finally

(5) the fact that the gravitational attraction of the Earth di­minishes with height.

The factors 2. 3, 4 and 5 do not begin to show to any large extent until the range is at least 40 miles while factor (1) shows always in the most disturbing manner. That factor, air resistance, is strangely enough least disturbing at the two extremes. It hardly shows for heavy projectiles over very short ranges, say up to 1500 yards, and for very heavy projectiles over very long ranges, say above 300 miles. In the former case air resistance does not have much influence because the projectile moves rather slowly, in the latter case it does not show too much because a very large section of the trajectory is, of necessity, lo­cated in layers of the atmosphere which are tenuous, to put it mildly.

Forgetting at first about these five factors—I am starting that sentence over again—the relationships are simple. If a gun fires straight up, its projectile will reach a certain height, which we'll call s. Fired at an angle of 45° with the same muz­zle velocity the projectile would land on the ground—provided there were no air resistance and the earth were flat—at a distance of 2 s from the gun. And the peak elevation along the trajectory would be s 2.

First we have to interest ourselves in vertical shots. The formula is simple, it is the square of the muz­zle velocity divided by 2 g. If we imagine a rather weak gun with a muzzle velocity of only 250 meters per second—about 818 feet per sec­ond—this works out as follows: 250 times 250 = 62,500 divided by 19.62 —which is 2 g expressed in metric units— = 3,185.5 meters. Since there are 1000 meters in one kilom­eter the result is 3.2 kilometers or about 10.615 feet.

When we first look at Table I we are interested only in the two col­umns at the left. Under the heading of vm which is meant to be read as "muzzle velocity" in this case, we find progressively larger velocities entered, expressed in kilometers per second. In the second column we find the altitudes that shells fired with these muzzle velocities would reach if there were no air resistance. For a reason which will be discussed soon the figures in the second column should not be taken too much at face value—beyond 1000 kilometers they are surely wrong as we'll see.

But now we come to high altitude and long-range rockets and the first question that comes up is whether there is a way of comparing rocket altitudes in some manner with the figures we just looked up in the table. A rocket, as everyone knows by now, does not start out with a high velocity but acquires it gradu­ally. It continues to rise with in­creasing acceleration and increasing speed until its fuel supply is ex­hausted. That point where the rocket motor stops working, marks the maximum velocity of a rocket, provided it is well designed. And because it marks the rocket's maximum velocity it is this point which must he compared to the gun muzzle if a comparison between guns and rockets is to be drawn.

The first job, obviously, is to find the point where the rocket reaches maximum velocity. Now look back at the table, this time we read the vm of the first column as "maximum velocity," the third column shows how high a rocket with a steady ac­celeration of 3 g will have climbed until reaching maximum velocity. A rocket accelerating with 3 g is pretty fast and the heights are rather con­siderable. The fourth column is not really required, it is there merely for interest's sake and shows the number of seconds the rocket needed to climb to that altitude. The next column is labeled s+h, and merely the addition of rocket altitude until vm is reached and the "gun altitude" which has to be added to it because a rocket with a velocity of, say, 1.5 kilometers per second—and with a no longer working motor—naturally behaves just like an artillery projec­tile with that muzzle velocity.

But while the figures in the col­umn s + h are fairly close to the truth for the interval between 40 and 600 kilometers they go more and more wrong the farther down in the column you go. The reason is that in that simplified calculation it had been assumed that the gravitational attraction of the earth is just as strong a thousand kilometers from the surface as it is at sea level. Of course it is actually weaker, getting gradually less and less. The very last column in the table, the one at the extreme right hand, takes this factor into consideration. It shows how high a rocket accelerating with 3 g would actually go, not counting air resistance.

Now we could imagine that the rocket has a booster unit which car­ries it to about twenty miles first in order to overcome the resistance of the densest layers of the atmosphere near the surface—in that case we could take the figures in the right-hand column virtually at face value.

It is interesting that the gradual reduction of gravity makes very lit­tle difference at first. The rocket which by the simplified method was calculated to climb to an altitude of 271.4 kilometers will actually go to 277 kilometers, the rocket calculated to go to 612 kilometers will actually go to 640 kilometers. These dif­ferences hardly count, the designer who designs a rocket for an altitude of 270 kilometers will be very happy to find it anywhere between 255 and 285 kilometers. But farther down in the column the differences be­tween detailed and simplified calcu­lation become more than just notice­able. The rocket with seven kilom­eters maximum velocity would go 3331 kilometers according to the simplified method, actually it would be 6140 kilometers.

The biggest possible difference is, of course, the one in the bottom row, where simplified calculation emerges with an altitude of about 8500 kilometers which would be roughly three quarters of the dia­meter of the Earth. Actually the altitude is plainly and simply in­finity, any distance in interplanetary space.

After having disposed of the al­titudes we can proceed to ranges, and begin again with guns where things are—or rather can be made to be—somewhat simpler. Diagram I illustrates the case of a 45° shot on a flat surface. The gun is lo­cated at O or zero, shooting to we don't know where and call it X. The distance SL is what the vertical altitude would be if the gun were standing in S. The peak elevation along the trajectory. SP, is half of SL. And the range OX is four times SP. The curve from O to X is theoretically a parabola and for this reason a range calculated in that manner, with an assumed flat liarth, may be and often is referred to as "parabolic range."

Table II shows in its second and third columns the parabolic ranges and peak elevations for a number of cases of muzzle velocity.

If vm does not mean muzzle velocity with respect to a gun pro­jectile, but means maximum velocity with respect to a rocket, we again need a correction. The rocket shot in Diagram I goes from O(1) to X(1). For the distance from O(1) to O the rocket motor is working and the rocket is under acceleration, but under 45° the rocket does not climb as high as it did vertically. The distance added to the range at take­off is the distance from O(1) to the point vertically below O which is called B on the diagram. Since the—shaded—triangle is an equila­teral triangle the distance from O to B is the same as that from O(1) to B, These, however, are merely para­bolic ranges, ranges calculated under the assumption that the Earth is flat. As long as the ranges are short that does not matter much, neither General Congreve of early war rocket fame nor Commander Dahlgren of naval gun fame were greatly troubled by the difference between "parabolic range" and "actual range". They still worried mainlyabout uniformity of propellant powders and uniformity of alloys, and they worried a little about air resistance which they found experimentally. We take uniformity of constructional materials for granted and we know a little more about air resistance although even now the experiment very often has the final say-so. But we are con­cerned about the difference between parabolic range and true range.

The same distance is added at the other end—not quite, since the line from X to X(1) should not be straight but curved—and for a first approximate result we find the rocket range to equal the gun range plus 2 OB. It has to be kept in mind, of course, that OB changes for every velocity which we assume. The results of such calculations can be seen in the two right-hand col­umns of Table II.

The point is that the curve of the trajectory is not a parabola but an ellipse. Diagram II shows how a 7000 mile rocket shot might really look. To calculate it is anything but a Sunday afternoon's diversion. First the ellipse belonging to a cer­tain velocity and angle of elevation has to be established. Then the angle OCS(1) can be found, and from that angle OCX. From then on it is only a half hour's job to find the distance OSX.

Unfortunately I am not able to add two columns to Table II giving ranges calculated from elliptical paths. This proved to he impossible for two reasons. The more impor­tant reason is that a man has just so much spare time and he can get along on just so little sleep. An additional reason is that I own noth­ing better that a 7-place logarithm table, which is not quite enough for such a job.

But I can offer a table of ap­proximations. Table III is calculated by means of a method illustrated on Diagram III. We see on Diagram III a section of the Earth's surface, with the flat parabolic OX range superimposed. The lines terminat­ing in arrowheads and marked C are lines pointing to the center of the Earth, they are what would be called vertical in the points O, K and X2. Now the parabolic range would end up in point X, but the projectile would still traverse the distance from X to X2. If we project the parabolic range onto the surface where it would fall between K and X,—but closer to X1—and add the height of X over the sur­face, XK to the distance OX1 we'll get a reasonable approximation of the distance OX2. Naturally all this is valid for 45° shots only.

But I'll not waste any more time with methods. Table III shows the parabolic ranges from Table II and the corrected ranges. The correc­tion was tested on an available figure calculated for an elliptical trajectory and a muzzle velocity of 820 meters per second. Calculated by the method shown in Diagram III the range would be 68,882 meters. The true range is 68,985 meters, if the figures were rounded up to the nearest full kilometer, namely 69, the difference would not show at all. At least in the lower ranges Table III cannot be too far off.

The result of all this work is that a missile of the type of the V-2 rocket would shoot some 31 kilo­meters—roughlv 20 miles—if its maximum velocity is 1/2 kilometer or 500 meters; that it would shoot some 80 kilometers—about 50 miles—if iis maximum velocity were only 300 meters—about 1000 feet—high­er than that of the first; that it would reach 127 kilometers—80 miles;—with a maximum velocity of 1000 meters per second and 288 kilometers—about 178.5 miles—with a maximum velocity of 1500 meters per second. The last figure agrees nicely with the actual per­formance of V-2 which had a maxi­mum velocity of 1600 meters per second and a range just short of 200 miles.

With a. maximum velocity of 2000 meters per second a range of about 523 kilometers—324 miles-—can be expected and with a maximum ve­locity of 3000 meters per second the range would jump to some 1230 kilometers or about 760 miles.

It might be of value at this point to compare the known or probable performances of the various kinds of shooting for several sets of ranges.

BATTLE RANGE, up to 8 miles. Within that range the use of atomic bombs or atomic warheads is im­possible, hence the lessons of World War II apply rather well. Within that range artillery has superiority of accuracy, while bombardment rockets have superiority of volume. Which will be chosen will depend entirely upon type of target and conditions of terrain et cetera, the point is that not one or the other but both must be supplied. Some of the jobs—like firing from air­craft—which were given to bom­bardment rockets will go to recoilless guns which are more accurate and weigh less. For any given size it will hold true almost always that the gun will weigh about as much as eight rounds of rocket ammunition. As soon as more than a dozen rounds can be carried by the plane, the weight factor will shift in favor of the recoilless gun, which has higher accuracy in its favor to be­gin with.

Guided missiles may turn out to be of even higher accuracy than artillery within battle range, pro­vided that guidance cannot be inter­fered with by the enemy.

LONG RANGE. This is beyond battle range up to about 120 miles. Within that range artillery is pos­sible but fantastically expensive. Moreover the volume of fire which long-range guns can deliver is small. Therefore artillery over such ranges could be considered only it the shells could carry atomic explosives. This does not sound likely, but, if it should prove possible, the verdict may well be in favor of artillery even for long range, since the probability of intercepting an ar­tillery shell is very slim indeed.

Because of the atomic bomb—but only for that reason—aerodynamically supported missiles—like V-l—and long-range rockets—like V-2—are of about equal value over ranges up to 120 miles. The competing facts are these: the missile is much cheaper to make, there were about 800 man hours of labor in a V-l flying bomb, but 13,000 man hours of labor in a V-2 rocket. With good interception, however, it might take many more man hours per missile which reaches the target than per rocket which reaches the target. If only chemical explosives were avail­able, the choice between rocket and missile would depend on the effec­tiveness of enemy interception. With atomic warheads it does not matter much, to intercept a missile over a city would be just as bad for that city as noninterception. The choice would actually be dic­tated mostly by the price and avail­ability of atomic explosives. If atomic explosives remain scarce and difficult to manufacture, or are out­lawed, the long-distance rocket would be the choice.

VERY LONG RANGE, beyond 120 miles. Here the field belongs virtually exclusively to the long-range rocket. Of course aerodynamically supported missiles could be made to travel 500 or 600 miles or more, but even if the missiles carry atomic warheads the chances for successful interception increase with distance. The more room there is between the point of inter­ception and the target, the safer it is to intercept the missile even at the risk of detonating the atomic war­head. Over all ranges the competi­tion between long-range rockets and piloted aircraft woidd depend en­tirely on the density and effective­ness of interception—an enemy who has grown weak enough to be bombed manually is no longer much of an enemy.

Since, by virtue of the atomic bomb, the long-range rocket has be­come the most reliable long-range weapon, it remains to look for limi­tations of the long-range rocket itself. There are mainly three. One is the increasing take-off weight with longer and longer ranges, which may come to a point that cannot be built any more. The other is the possibility of the rocket's "incineration" during descent. The third is the problem of guiding.

The first question is answered by Table IV. Across the top of that table a number of maximum veloci­ties have been entered along with the ranges obtained by these maxi­mum velocities. At the left a set of exhaust velocities for the rocket motor have been entered. The figures under the word mass-ratio then indicate the ratio between take­off weight of the rocket and the "weight of arrival", meaning empty rocket plus warhead.

If, for example, your rocket motor produces an exhaust velocity of 2000 meters per second—the V-2 motor did that—and you have to fire over a range of 31 kilometers, the take-off weight of the rocket has to be 1.3 times the "weight of ar­rival". If you want to fire over a range of 127 kilometers, the take­off weight has to be 1.6 times the "weight of arrival" and so on. Actually the take-off weights have to be somewhat higher, because the table assumes that there is no air resistance. This increase would show the more the shorter the range.

At present there is no practicable rocket motor known which can even produce an exhaust velocity of 3000 meters per second. And even in theory 4000 meters per second is the limit for chemical fuels. If atomic energy could be utilized for propulsion too, the exhaust velocity might be stepped up to 20,000 meters per second, the table gives the mass-ratios for these hypo­thetical high exhaust velocities.

But the table also shows one factor which is highly interesting; it means that for most practical purposes there is a limit to the exhaust velocity which needs to be attained. Let's pick out a case from the table which, will illustrate what I mean. In the column below the maximum velocity of 2000 meters per second you find that the mass-ratio would have to be 54 to 1 if the exhaust velocity available were only 500 meters per second. That, obviously, is too high when it comes to design and construction. If an exhaust velocity of 1000 meters per second were available, the mass-ratio required drops to 7.4 to 1. This is already within the realm of what the engineering department could accomplish although so far no rocket of such a high mass-ratio has been built. If the exhaust veloc­ity were increased to 3000 meters per second, the mass-ratio required would be roughly 2: 1 which is quite easy to build—V-2 had better than 3 to 1. If the exhaust velocity were increased to 4000 meters per second the mass-ratio required would be only 1.64 to 1 which is, of course, still easier to build.

To increase the exhaust velocity from 4000 meters per second to 5000 meters per second might be a very difficult job, but the gain in mass-ratio is not too important any more. It is now 1.49 to 1 instead of 1.64 to 1. Such a gain would hardly simplify construction, while the increase in exhaust velocity may be enormously difficult.

The same reasoning can be ap­plied to almost any other column in the table, whatever the example there comes a point where the gains in reduced mass-ratio from in­creased exhaust velocity become unimportant.

To obtain an easily built mass-ratio it is sufficient to have an ex­haust velocity twice as high as the maximum velocity required. Higher exhaust velocities are nice, provided they can be had cheaply. But only then.

The combination of exhaust veloc­ities which can be had, and of mass ratios which can be easily built, limits the range of the single long-range rocket to about 700 miles for present day fuels. The emphasis in this statement is on the word "single", a rocket with booster units for take-off, or multiple rockets could naturally obtain longer ranges.

But the longer the range the more serious the danger of "incineration" by which term I mean the heating of the rocket caused by compressing the air in its path. Londoners under V-2 fire on occasion saw the de­scending rockets glowing dull red. Every once in a while the residue of fuel in the tanks exploded the rocket before it reached the ground. The Germans had to take the pre­caution of choosing a high-explo­sive for the warhead which can be heated up very considerably without exploding.

This factor naturally increases with increasing distance since in­creased distance means increased maximum velocity. Now the rocket is excellently suited to cope with this factor during take-off. The closer to the surface, the denser the air, and the slower the rocket. There is virtually no danger of heating up on the ascent and it helps that the fuel tanks, still fairly full, could also absorb a goodly quantity of heat with effects that are bene­ficial rather than detrimental. Be­sides, the velocity at take-off could be adjusted to avoid such danger if it should become apparent.

But you can't adjust the velocity of the falling rocket.

Pulled down by gravity it has the tendency to increase its velocity more and more, entering denser and ever denser layers of the atmos­phere in the process. It might well be that long distance war rockets will burn up when fired beyond a certain—and as yet undetermined—range.

But it is also very likely that the warhead could be insulated suffi­ciently to reach the ground in one piece, even if the rocket does not.

And that brings us to the limita­tions imposed upon guiding.

A long-range rocket can be guided best while climbing, when the rocket motor is working. After the rocket motor has been shut off there is no way of guiding the rocket any more, not because it is no longer powered—it is still powered by very large quantities of kinetic energy—but because the air around the rocket, if any, is far too thin to make the rocket respond to movements of the fins. Guiding becomes possible to a certain extent on the way down, when denser layers of the atmos­phere have been reached again. But when that happens the rocket is so far from the firing range thai it is below the horizon. To guide it on the way down would require the presence of a guiding station not too far from the point of im­pact, for example high flying air­craft circling in the general vicinity of the target.

Of course you might say that they would not circle there very long if the enemy is even mildly alert—and I agree with that state­ment. The solution to the guiding on the descending path might, but only just might, lie in the orbital rocket. If a rocket attains a maxi­mum velocity of 8,000 meters per second, it will not return to earth any more but circle the earth inde­finitely in an orbit outside the atmosphere without any fuel ex­penditure. If we imagine three such orbital rockets circling the Earth, spaced 120° apart, one of the stations would have any given point on Earth accessible to radar waves at any moment.

By the time technology has pro­gressed to establishing orbital observation rockets it automatically has also progressed to orbital war rockets with atomic warheads. That being the case, the orbital observa­tion rockets would not need to pick up long-distance rockets fired from somewhere on Earth and guide them—they could just dircct orbital war rockets down to their targets.

But if two countries of about equally highly developed technology were preparing for war with each other, even the orbital rockets would not constitute much of an advan­tage. Both the observation rockets and the orbital war rockets would be in well-determined astronomical orbits about the Earth, without power to influence these orbits ex­cept within relatively narrow limits, also well-determined.

Neither their positions nor their numbers could be kept secret, they would be quickly revealed to search radars of the other nation. And it would not be too hard to have a dozen interception missiles ready for each one of the orbital rockets, to be released at the very first sign of the opening of hostilities, before any of the orbital war rockets had time to fall very far.


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