US 3727861 A
An aerial weapon is provided for the suppression of antiaircraft artillery fire against an air attack. This concept has been called various names in the past, notably AFIRM standing for Anti-Flak InfraRed Missile. A first rocket delivers the missile which descends on a parachute until the heat of an antiaircraft gun is sensed. A second rocket propels the missile to target under control of heat sensing guidance and control unit.
Description (OCR text may contain errors)
Elite States atent m1 Swarm [4 1 Apr. 17, 1973 METHOD AND APPTUS FOR SUPPRESSION OF ANTHAIRCa L i FIRE Inventor:
Edwin G. Swann, China Lake, Calif.
The United States of America as represented by the Secretary of the Navy Filed: Mar. 5, 1970 Appl. No.: 22,101
Primary Examiner-Samuel Feinberg AltorneyR. S. Sciascia, Roy Miller and Gerald F. Baker  ABSTRACT An aerial weapon is provided for the suppression of antiaircraft artillery fire against an air attack. This concept has been called various names in the past, notably AFlRM standing for Anti-Flak InfraRed Missile. A first rocket delivers the missile which descends on a parachute until the heat of an antiaircraft gun is sensed. A second rocket propels the missile to target under control of heat sensing guidance and control unit.
4 Claims, 8 Drawing Figures PATENTEDAPR 1 mm 3,727. as 1 SHEET 1 [IF 3 FIGQl EDWIN G. SWANN INVENTOR.
ROY MILLER ATTORNEY GERALD E BAKER AGENT PATENTED 1 H975 3. 727. 86 l SHEET 3 [1F 3 METHOD AND APPARATUS FOR SUPPRESSION OF ANTIAIRCRAFT FIRE BACKGROUND OF THE INVENTION:
Air attack during prolonged conflict has encoun tered increasing resistance from ground defenses. Such ground defenses include rapid fire guns ranging from machine guns to heavy artillery generally employing various types of fire control systems. The guns are disposed in an area to be defended in accordance with a doctrine of employment which may be detectable after the fact but which may well be very difficult to predict should the enemy find it desirable to conceal his tactics. Alternatives that are available to the enemy, for example, are: (a) disposition close in or dispersed on the approaches to a target area; (b) concealment of gun sites with heavy camouflage or nonconcealment coupled with construction of decoy sites; (c) use of barrage fire as opposed to the use of tracking fire. The effective employment of antiaircraft artillery and light guns has three distinct but related effects on the attack. Some aircraft are hit and suffer damage or destruction. To avoid the first effect, or to ameliorate it, the attackers deliver their weapons from greater distances thus reducing accuracy and effectiveness. Finally, in attempting to stay out of range of artillery, the attacking aircraft are caused to fly into the detection and launch envelopes of surface to air missile systems.
The objective of flak suppression is to significantly reduce the effectiveness of antiaircraft artillery and light guns. The most direct way of achieving this objective is to destroy enemy gun systems by direct attack. It is operationally difficult to apply this approach because it involves the destruction of a very large umber of relatively invulnerable targets, and because it places the primary target of interest second in the sequence of attacks. Furthermore, it more than ever would lead to a demand for a specially designed weapon to overcome the invulnerability of the targets and to aid in reducing the vulnerability of the aircraft while making such attacks. Finally, it plays into the hands of the enemy whose objective in the employment of antiaircraft artillery is to reduce he effectiveness of air attacks on his primary targets. A less direct way to achieve the objective of flak suppression is to deter he enemy from the use of his guns during the periods when our attack aircraft are most vulnerable, that period when they are approaching and delivering on the primary target. Deterrence of this sort can be achieved if there is a threat of direct retaliation triggered by the undesired action. In other words, if the attacking aircraft can present a threat to the gun systems that they will be attacked, if and when they open fire during some limited period of time, then some measure of suppression will be achieved. This is the nature of the method that is described in this invention.
SUMMARY OF THE INVENTION Light guns and artillery that have been evolved through a long history for the purpose of shooting at airplanes have certain characteristics that are readily distinguished. First, they are guns, generally of high muzzle velocity. When in use they radiate large quantities of energy of acoustic and electromagnetic nature resulting from imperfect conversion of the stored chemical energy of the propellant to kinetic energy of 0 sound pulses. These are shortly followed by nearly omnidirectional radiation in the infrared from the muzzle, barrel, breech parts and expended ammunition cases. Typically this radiation becomes significant after 10 to 20 round of rapid fire independently of the calibre of the gun. This general behavior stems from the fact that the heat capacity of the gun is roughly directly related to the amount of energy that is expended in each firing. The thermal lag for the elevated temperatures to reach the outer surfaces of the gun parts is nearly exactly compensated for by the loWer rates of fire of large guns over small guns. Some early exploration of the feasibility of detecting guns by their infrared radiation has been accomplished. This primarily was accomplished in tests conducted as Randsburg Wash Test Range of the Naval Weapons Center. The concept that is described herein depends on the above inherent characteristics of antiaircraft artillery.
According to the invention a flak suppression aircraft launches parachute missiles toward flak sites that cover the primary target and the egress route from it. Even if the flak sites are undetectable, approach and egress corridors can be seeded with these missiles. A plurality of weapons are suspended over the flak sites on their deployed parachutes. When the following strike aircraft run in on the target, opening fire from the guns is detected acoustically by the missile, the direction to the strongest source is detected and the infrared seeker of the detecting missile is trained in that direction. A small angle search is performed by the seeker until a lock-on is obtained. When lock-on is acquired by the infrared seeker, he second rocket is initiated and the missile separated from its parachute. The missile then homes on the source of the infrared radiation and, even if the gun ceases fire, the missile is still able to home on the energy that continues to be radiated.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG. I is a plan view, partly in section of a preferred embodiment of a weapon useable in the disclosed system;
FIG. 2 is a plan view of the weapon of FIG. 1 in a first stage of deployment;
FIG. 3 is a sketch depicting terrain in a typical area;
FIG. 4 is a sketch depicting a closer view of the area of FIG. 3;
FIGS. 5 and 6 are sketches depicting yet closer view of the area;
FIG. 7 is a view similar to FIG. 2 showing a deployed weapon suspended by parachute; and
FIG. 8 is a view similar to FIG. 7 just after release of the weapon.
DESCRIPTION OF THE INVENTION Av missile according to a preferred embodiment of the invention, is shown at in FIG. 1. The missile 10 has two rocket motors 12, 14. The first (12) is the larger of the two and serves to emplace the missile. Even with this rocket 12 the missile is a relatively low velocity projectile. Approximately 15 pounds of solid propellant (18) gives it a boost velocity over the launch aircraft velocity of about 500 feet per second. The missile 10 is launched on an upward trajectory (see FIG. 4) to give it an altitude gain of a few thousand feet at a point 2 to 4 miles from the launch point. As the missile begins the downward part of its trajectory a barometric sensor 22 separates the first rocket motor 12 and deploys the parachute 24. The parachute 24 is designed to provide a descent rate of 25 to 50 feet per second. While falling, the missile listens for gunfire from an area that is covered by a cone of about 45 degrees half angle below it.
The missile listening referred to is based on the use of acoustic defection of gun fire to locate targets. This is accomplished by four acoustic detectors (see FIG. 2) that are mounted on folding arms 32. During missile flight these detector arms 32 are folded along the skin 16 of the missile and lie in recessed grooves 34. When the missile 10 is suspended from its parachute 24 its acoustic detector arms 32 are unfolded or hinged forward forming quadrature pairs. Direction of the sound arrival is determined by arrival time differences in each of the two quadrature planes. The location direction thus determined for sound pulses is used to slave the infrared seeker 20 in a limited area search. With a 4 foot base line and maximum desired look angles of 45 degrees, time differences of the order of zero to 3 milliseconds will be measured. It should be possible to measure the arrival time differences in the very quiet environment of a parachute fall with an accuracy of plus or minus 0.25 milliseconds. If this can be achieved a search of a conical angle of 5 degrees will be adequate for the infrared seeker. To give added discrimination against background noise and spurious signals an integration of five to ten pulses will be required for the slaving of the seeker. In this way the seeker will not be slaved to search for targets that are not likely to radiate sufficiently in the infrared to serve as good targets.
The second rocket motor 14 of the missile is ignited upon defection and lock-on by the infrared seeker 20. It separates the parachute 24 and propels the missile 10 toward the target. This rocket 14 is relatively low performance having about 10 pounds of propellant 28 to provide the missile with a velocity of about 400 feet per second. The missile warhead 26 weighs about 50 pounds and is designed primarily for personnel kill and secondarily for gun damage.
Missile Characteristics Length, in. Diameter, in. 6 Fin span, in. 18 Acoustic span, in. 48 Total weight lb. 200 Warhead weight, lb. 50 lst rocket prop., lb. 15 2nd rocket prop., lb. 10 Launch range, n. mi. 2 to 4 Launch altitude, k ft. 2 to 15 Operating alt., k ft. 15 to 3 Parachute rate, ft/sec 25 to 50 Acoustic look angle degrees 45 IR Seeker range, n. mi. 4 Possible cost, 5000.00
What is claimed is: 1. A weapons system comprising: a plurality of missiles;
means for deploying said missiles over a selected area; said means for deploying including hover means maintaining said missiles over said area for a finite period of time; gunfire detection means on said missiles affected by the sound of gunfire in said area to produce a signal output; said detection means including means responsive to said signal, or separating said missile from said hover means; guidance means in said missiles affected by an aspect of a gun installation and effective to cause said missile when separated from said hover means to home on a gun installation site in said area. 2. A weapons system according to claim 1 wherein said hover means comprises a parachute.
3. A weapons system according to claim 2 wherein said guidance means comprises heat sensitive means.
4. A weapons system according to claim 1 wherein said guidance means includes heat sensitive means.