Radar Rockets
July 1946 Radio-Craft

July 1946 Radio-Craft [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

During World War II, Germany terrorized Europe with it rocket bombs, most notably the V-1 Buzz Bomb and the V-2 Rocket. The "V" prefix, BTW, stands for Vergeltungswaffe, translated as "vengeance weapon," or "retribution weapon." Both "vengeance" and "retribution" are really misnomers since it was Germany that was the aggressor in both WWI and WWII. The vengeance or retribution in Hitler's view was likely the punishment and restrictions imposed on Germany by the Treaty of Versailles for its vicious and inhumane behavior before and during World War I. History shows they doubled down on it during World War II. But I digress. This 1946 article in Radio-Craft magazine proposes a scheme for a "radar rocket" system that could detect, acquire, and intercept an enemy rocket bomb in flight - a concept that was never really successful until the Patriot Missile was deployed in the 1990s as part of the Strategic Defense Initiative (SDI, aka "Star Wars"). This "Remote Control Weapons" editorial appeared a year earlier in the August 1945 issue of Radio-Craft.

Radar Rockets - May Be the Answer to the Rocket Bomb

By H. W. Secor

One of the problems now engaging the attention of our military experts is to provide a strong defensive weapon to combat flying rockets and bombs. In the next war - should one occur - the enemy will loose a barrage of long-range rocket bombs on our cities and vital industrial plants. Some of these will doubtless be atomic bombs. High speed jet-propelled fighter planes may knock down some of them, but some surer way of fighting such an attack is needed. Counter-attack rockets immediately suggest themselves.

Microwave radars can be designed to direct the counter-attack rocket so that it literally chases the enemy rocket and explodes as it nears the missile, thus destroying it before it has a chance to reach its target.

Figure 1 shows a tentative plan for the positioning of the radar apparatus in the rocket, also the disposition of the explosive and the control mechanism.

It may be objected that the tremendous speeds of rockets may not allow time for such defense, but this is not the case. Even at a speed of 3,000 miles per hour, a rocket launched from the (for rockets) close range of 500 miles would take a minimum of ten minutes to reach its target. Actually the time taken would be much longer because of the curved trajectory. Trans-Atlantic rockets would travel much more than an hour.

The time allowed for launching the counter-attack rockets can be lengthened by erecting radar outpost listening stations at such points as Iceland, Greenland, Bermuda and other outlying places (also at similar Pacific stations) for spotting the approach of enemy rocket bombs. (Fig. 2.) These stations would be continually on watch. The information gathered by them would be relayed automatically to the main base station on the mainland by radio, and counter-attack radarockets sent out to apprehend the enemy missile and des-troy it before it reached within striking distance of the mainland.

Another plan is shown in Fig. 3 - an airborne long-range radar station. The flying radar station would maintain radio contact with the ground bases for transmission of target location data; an accurate location "fix" or position for the enemy rocket can be supplied at any moment, or its course may be plotted continuously. The station directing the radarocket can then combine the information received from two or more of these spotters to plot the coming rocket's trajectory and aim a fighter rocket in the proper direction to meet it. Electronic equipment could do all this automatically and the release would be almost instantaneous.

The radarocket would ascend rapidly, using jet propulsion. Upon approaching the target it could be detonated by the same means so successfully used in the thousands of proximity fuze shells employed against the enemy in the war just ended. In this device a radio wave was sent by the shell's miniature radio transmitter; reflected radio waves picked up from the enemy target (such as a plane) by the receiving set carried in the shell caused it to detonate when it came to within a distance of about seventy feet of the target.

In another plan the course of oncoming enemy missiles is plotted by radar and the launcher carefully aimed so the radarocket will intercept it. When this bloodhound of the air comes within a reasonable distance of the enemy bomb or flying rocket, it sends out a microwave which is reflected by the enemy missile (Fig. 4). These reflected waves are picked up by a receiver carried by the radarocket and keep it on the trail of the target.

This may sound far-fetched, but we have only to recall that some radars used in World War II would track an airplane in flight and automatically aim antiaircraft guns at it. These radars used conical scanning to achieve this feat.

The principle of conical scanning (Fig. 5) is that of using a reflector to concentrate or beam a pulsed signal in a lobe pattern - and then cause the lobe to rotate around the axis of the reflector,

A tiny dipole antenna is mounted off-center in the reflector and is rotated by a small spinning motor. Only two successive positions (5-a) of the lobe are shown, for the sake of clearness. Note (5-b) that the rotating radio lobe projected by the dipole brackets the enemy target (a flying bomb for example).

Figure 6-a shows how the strength of the reflected echo signal from the target varies for different positions of the lobe, when the target is off the center-line of the reflector. When the target is on the reflector center-line (6-b) the strength of each reflected signal is of equal amplitude. Thus the pulsed signal actually scans the target.

The varying strength of the reflected signal actuates a correcting mechanism (operating the vertical and horizontal rudders, or firing "course-correcting" auxiliary jets on either side of the radarocket).

The revolving lobe describes a circular path (forming a cone as shown in Fig. 5-c). A target located on the reflector axis line gives a resultant echo signal (on the receiver) having an identical amplitude for every position of the rotating lobe. If the target is not on the center-line of the reflector axis, the echo signal will vary in amplitude sinusoidally as the lobe is rotated. Whenever the lobe's center (or axis-line) approaches the target there is an increased strength of reflected signal. As the lobe rotates further, so that its axis or center line recedes from the target focal line, a weaker signal results. The direction of the target from the reflector axis is thus indicated by the relative phase of the variation or rise and fall in strength of the received echo signal.

Fig. 7 shows two positions of the rotating lobe and the relative strengths of signals reflected from the target in different positions. (See also Fig. 4).

The preponderant strength of signal received on the radarocket (when the target is off to one side of the reflector axis) is caused to correct the course of the rocket. With the conical scanning method (which was employed on the SCR-584 Radar) applied to the flying bomb, it should hit the enemy target - once it comes within range.

When reflected signals of varying strengths are picked up on the radarocket's receiver (for a target off the centerline of the reflector axis) these signals are integrated through suitable circuits fed into an amplidyne control amplifier and finally impressed on an amplidyne generator (controller). The rotor of the generator turns in accordance with the degree and polarity of the impressed current and relays this position to a servo motor in the rear of the radarocket. This servo may operate the vertical and horizontal rudders (or fire auxiliary course-correcting rockets).

The problem of identifying an enemy rocket poses a nice problem for the engineers. By making careful observations of the relative speed and the course followed by a rocket over a given period of time, it becomes possible to plot its probable course, and be prepared to shoot it down long before it comes near enough to be dangerous.

Planes might also be used as carrier devices, bringing rockets to within a few hundred miles and releasing them. However, if all friendly planes and rocket devices are fitted with IFF (Identification, Friend or Foe - See Radio-Craft February, 1946) any flying craft which did not give a satisfactory response would at once be classified as enemy and counter-attack rockets sent out after it.

These precautions would be necessary only in peacetime (during periods when surprise attack might be feared). In war, all friendly planes would be grounded, and whereabouts and movements of friendly military planes definitely known. Thus any unknowns could be classed definitely as enemy.

The idea for the radarocket was discussed with an expert who had considerable experience with radar sets used by our fighter planes in hunting down enemy planes at night or in foggy weather. It seemed from the results obtained with radar in aerial warfare that the radarocket automatic direction control could be depended upon to work up to distances of about a mile.

In radar reflections the area of the target which is to reflect the wave projected against it has a great deal to do with the strength of the signal sent back to the receiver. The larger the target the stronger the reflected signal. The reflecting area of the enemy flying bomb would admittedly be rather small, but modern radar has demonstrated almost unbelievable sensitivity; in some cases the tiny periscope of an enemy submarine was a sufficient target to reflect the radar wave sent from a scout plane several miles distant.

Posted October 11, 2021