US3026806A - Ballistic missile nose cone - Google Patents

Description

March 27, 1962 A. RUNTON ET AL 3,026,806

BALLISTIC MISSILE NOSE CONE Filed March 22, 1957 jog-" 3 Sheets-Sheet l /4 GE/VEEAIE'D All? BDU/VOARY 6A 5 PROZZ'CT/Vf 22 L A YER 8 LA YER A 24 A T'TOP/Vfy March 27, 1962 A. RUNTON ET AL BALLISTIC MISSILE NOSE CONE m mw an m 4 J 3 0 A Filed March 22, 1957 A TI'OR/VE Y March 27, 1962 1.. A. RUNTON ET AL 3,025,306

BALLISTIC MISSILE NOSE CONE 3 Sheets-Sheet 3 Filed March 22, 1957 ATTORNEY.

3,026,806 BALLISTIC MISSILE NOSE CONE Leslie A. Runton, Middle Haddam, and Henry C. Morton,

Branford, Cnn., assignors to The Russell Manufacturing Company, Middletown, C0nn., a corporation of Connecticut Filed Mar. 22, 1957, Ser. No. 647,838 6 Claims. (Cl. 102-925) The present invention relates to the art of missiles of the long range type known as intercontinental ballistic missiles and usually referred toas I C BM, and more par- W ticularly to a method and means of protecting the war heads on such missiles against the destructive effect of aerodynamic heating during reentry into the air layer surrounding the earth.

In current rocket-propelled ballistic missiles of the ICBM type employing fuel propellants, geographical considerations dictate a range of as much as 50 00 miles. To attain such long ranges, it is necessary to propel the missile to an extremely high altitude. At the peak of its ascent, the missile will reach a level well above the earths atmosphere and at the upper level of the ionosphere, where the absolute pressure is almost zero and the resistance to the forward flight of the missile is almost nil. Once the thrust of its rocket engine is exhausted and the missile has reached this high altitude, it follows a freefailing trajectory course towards the target, obtaining no lift from wings or similar surfaces.

During initial upward flight to the ionosphere, the speed of the missile is not great enough to pose any serious thermal problems. However, at the altitude of 50 miles, the absolute pressure begins to increase progressively during descent, until the earths surface is reached. At the present time, missiles reentering the air layer during downward flight, attain speeds equal to Mach 5 or 3700 miles per hour, and in the near future, missiles are expected to be designed which will attain speeds as high as Mach 18, equivalent to approximately 13,000 miles per hour. At Mach 5, the heating rate could be in the neighborhood of 100 B.t.u./ft. /sec. and at Mach 18, the heating rate could be 1000 B.t.u./ft. /sec. for a period of 20 seconds, these heating rates being produced by the high temperature of the air boundary layer ahead of the missile resulting from the compression of air, which temperature can be as high as 12,000 F. at 11,000 miles per hour.

It is seen, therefore, that a challenging problem in the design of intercontinental missiles is the tendency of the atmosphere to burn them up as they descend towards the earth. At the extreme speeds with which the missiles descend through the atmosphere, they suffer aerodynamic heating and abrading due to the extremely high skin temperatures developed in and by the air boundary layer immediately encompassing the missile, and this condition is increasingly critical and greatly aggravated at high Mach numbers as to constitute a serious thermal barrier.

It is obvious that the missile must have a low drag-toweight ratio during its upward flight through the troposphere, the tropopause, the stratosphere and the ionosphere. For that purpose, a nose cone tapering to a point is desirable during the ascent of the missile. Nevertheless, upon reentry into the stratosphere and during its descent towards the earth, a high drag-to-weight ratio is required to reduce the speed of the missile and consequently its heating rate. However, the downward speed of the missile must not be reduced to the point where it can be intercepted.

The thermal destruction of parts of the nose cone of the missile during descent is not undesirable, since it serves to increase the drag-to-weight ratio of the missile during ice this descent. However, the high temperature developed during the course of this destruction transmitted to the war head may be ruinous.

One object of the present invention is to provide a new and improved method and means for protecting the war head of an intercontinental ballistic missile against the destructive effect of aerodynamic heating during downward flight towards its target.

Another object of the invention is to provide a new and improved ICBM nose cone, which is designed to afford low drag-to-weight ratio during upward flight and high drag-to-wei ht ratio during its downward flight through the air layers, and which is designed to create a protective shield around the war head against overheating during this downward flight.

In accordance with certain features of the present invention, during the downward flight of the missile, a protective cooling and shielding gas stream is created around the nose cone and between the surface of the missile and the high temperature air boundary layer, preventing thereby transmission of the high temperatures from said air boundary layer to the war head. For that purpose, the nose cone is made of vaporizable material and/or contains vaporizable material, which at the high temperature created during descent, forms a stable gas or vapor. This gas is directed to or formed at the periphery of the nose cone, and is developed by the movement of the missile into a sheathing stream surrounding the surface of the nose cone and war head and separating the high temperature air boundary layer from the missile surface. Since this protective sheeting gas stream is at a much lower temperature than that of the air boundary layer, it acts not only as a protective separating sheath against the thermal destructive action of this air boundary layer but also due to its comparatively low temperature, as a coolant for the forepart of the missile.

Also, since the vaporizing of the material of the nose cone and/or material in said nose cone requires heat. and the conversion from a liquid or solid state to vapor state is effected without change in sensible heat, it is seen that this vaporizing action uses up heat which otherwise would be directed to the raising of temperatures to destructive levels.

In carrying out certain features of the invention described, there is provided in the nose cone a chamber enclosing a material which under the action of the heat transmitted thereto by aerodynamic friction is converted into a gas during the downward flight of the missile. At least a part of the nose cone is porous to permit this gas to sweat or flow outwardly therethrough to the outer surface and to form thereby a protective cooling stream around the forepart of the missile disassociating the high temperature air boundary layer from intimate contact with the nose cone.

In accordance with certain features of the present invention, the nose cone comprises a forward primary nose cone section tapering towards a point for streamline contouring and eifective during upward initial flight towards and through the ionosphere to afford low drag-to-weight ratio during this flight, and a secondary nose cone with a blunt or high resistive contour located behind the primary nose cone section, so that it is not effective during the initial upward flight of the missile, but is rendered automatically effective during downward flight to slow down the speed of the missile to a point where overheating of the war head is prevented but not to the point where the missile can be intercepted. The primary nose cone section is made of material which will fuse, burn otf or disintegrate under the heat generated as the missile moves downward through the air layers, causing thereby the secondary nose cone section to be exposed as the leading element on the missile. The primary and secondary nose cone sections may be made of different materials having different disintegrating or fusing temperatures and arranged along said sections to effect disintegration of the parts in successive downward flight stages.

As an additional feature, to maintain maximum heat sink ability, there is located between the back of the high drag secondary nose cone section and the war head a metal shell of high conductivity to dissipate the heat in the regions of the nose cone closest to the air boundary layer. To further thermally shield the war head from the nose cone, there is interposed therebetween an insulating sheet combined with a highly reflective metal foil.

As a further feature, the nose cone contains a material which is decomposed under high temperatures, providing an endothermic reaction. The nose cone is designed to cause the air from the high temperature boundary layer to course through said material. The high temperature of this air decomposes the material and in the process absorbs heat. As a result the air is cooled. This cooled air is used to carry away heat from parts of the nose cone close to the war head.

Various other objects, features and advantages of the invention are apparent from the following particular description and from the accompanying drawings, in which FIG. 1 is an axial section through the forepart of a missile of the ICBM type constituting one embodiment of the present invention and shown prior to upward flight or during upward flight, while its primary nose cone section is intact;

FIG. 2 is an axial section of the same missile but shown during the early stages of its descent through the air layers and after the primary nose cone section has been fused and abraded off the missile;

FIG. 3 is an axial section of the same missile but shown during a later stage of its descent through the air layer, when more of its secondary nose cone section has been fused and abraded off the missile;

FIG. 4 is an axial section of the same missile but shown during the last stages of its descent, when a major part of its secondary nose cone section has been fused and abraded off the missile;

FIG. 5 is a transverse section of the missile taken on lines 5-5 of FIG. 1;

FIG. 6 is a section of the insulating sheet employed between the war head and the nose cone;

FIG. 7 is an axial section through the forepart of a missile of the ICBM type constituting another embodiment of the present invention and shown prior to upward flight or during upward flight, while its primary nose section is intact; and

FIG. 8 is an axial section through the forepart of a missile of the ICBM type constituting a still further embodiment of the present invention and shown prior to upward flight or during upward flight, while its primary nose section is intact.

Referring to FIG. 1 of the drawings, there is shown an intercontinental ballistic missile of the rocket-propelled type. This missile of elongated generally cylindrical shape is shown provided with the usual war head 10 having a forepart 11, which tapers towards a flat forward end 12 and which is shown substantially in the form of a truncated cone. Secured to the end of this war head 10 is a nose cone 13 embodying the present invention. This nose 13 comprises generally a primary nose cone section 14 and a secondary nose cone section 15. V

The primary nose cone section 14 is in the form of a solid conical cap provided with a concave recess 16 to seat conformably on the end of the secondary nose cone section and terminating in a sharp point 17 to afford a low drag-to-weight ratio in its upward flight and to allow, thereby, the missile to go up with a minimum of resistance,

The primary nose cone section 14 is constructed of material which will withstand the heat generated therein during upward flight, but which will burn, fuse and disintegrate as the result' of the heat of higher temperature generated during the early stages of its downward flight when passing through the stratosphere, thereby blunting off the leading end of the missile to slow down its descent. For that purpose, the primary nose cone section 14 is made of a metal, which has high heat conductivity and which desirably fuses approximately at a temperature between 1500 and 3000 F. Preferably, the primary nose cone section 14 is made of powdered metal, which can be sintered to form a coherent body. Copper serves this purpose admirably, since it has high thermal conductivity and sinters at a temperature of about 1750" F. Iron powder or alloys of this powder and/or of copper can also be employed. Sintered iron powder alloys, for example, fuse at around 2800 F.

The sintering operation can be effected by the usual method employed in powder metallurgy in which metal powders with a lubricant, such as graphite or stearic acid, are compressed and molded into the desired shape and heated to fuse the metal particles into a coherent mass of this shape. The resulting structure will have a porosity, which will depend on the size of the metal particles and the amount of variation in the sizes of the particles and which will be desirable for the reasons to be described.

The secondary nose cone section 15 is in the form of a cup invertedly seated on and over the war head 10 and comprises a head portion 20 and a skirt portion 2f interconnected to form a unit. The head portion 20 of the secondary nose cone section 15 tapers towards a rounded end 22, which conformably fits into the recess 16 of the primary nose cone section 14 and which is brazed to the primary nose cone section 14 in the manner to be described to form a unit therewith. This head portion 20 of the secondary nose cone section 15 defines a chamber 23 serving to hold a material 24 which vaporizes under the action of the heat generated during the descent of the missile. The material in the embodiment of the invention shown in FIG. 1 is a solid or liquid vaporizable under the action of heat generated during descent, to produce a gas which escapes under pressure through the walls of the secondary nose cone section 15 in the manner to be described, and which consequently forms a cooling sheathing stream immediately around the forepart of the missile to disassociate the high temperature air boundary layer from the missile head. Suitable liquids or solids for the purpose may be titanium hydride, lithium hydride or beryllium hydride. Water, anhydrous liquid ammonia and mercury may be used. Also suitable are vaporizable metallic elements such as sodium, which melt at high temperature and turn into gas as well as solid compounds which sublime directly into a gaseous state.

The material of the secondary nose cone section 15 is of the sintered type and desirably has a higher fusing point than the primary nose cone section 14, preferably over 2000 F., to prevent too rapid disintegration of said secondary nose cone section during descent and to assure maintenance of the integrity of at least the skirt part 21 of said secondary nose cone section immediately surrounding the war head 10 up to the point of destination of the missile. A suitable material is stainless steel, sintered to render it porous and to facilitate its manufacture into the desired shape. For example, a stainless steel powder, such as that known as Iconel X (International Nickel) comprising basically about nickel, 13% chromium and 6% iron is considered highly suitable. Other sintered materials which may be used for the secondary nose cone section 15 are titanium carbide, tungsten carbide, silicon carbide, aluminum oxide and cerametallic combinations. Carbon can also be used alone or in combination with one or more of the sinterqd,

ceramic and metal compounds described. Also, usable for the purpose are pure quartz and such porcelain mixtures as are currently employed in furnaces where metals are reduced to the molten stage, exemplified by the prodnot sold under the trademark Carbox.

The sintering of the particles into a coherent shaped mass in the construction of the secondary nose cone section 15 is carried out in a manner similar to that described in connection with the production of the primary nose cone section 14 and produces a unit with a porous wall 26 defining the chamber 23 for the vaporizable material 24. The permeability of this wall 26 permits the gas produced by vaporization of the material 24 enclosed in the chamber 23 to flow under pressure through said wall to the surface of the missile head. The porosity of this nose cone section 15 can be increased if required by employing sin-terable particles of varying sizes.

The latent heat required to vaporize the material 24 chills the mass of metal or other material of which the secondary nose cone section 15 is constituted and thereby dissipates and/ or averages out quickly the heat transmitted from the high temperature boundary layer without a corresponding rise in temperature. The secondary nose cone section 15 in conjunction with the material 24 forming part thereof, constitutes a primary heat sink helping to dissipate the heat transmitted from the air boundary layer.

It is desirable that the gas produced from the vaporizable material 24 be directed through the wall 26 mainly towards the tip 22 of the secondary nose cone section 15 to cause the protective missile gas curtain to originate at this point for distribution and development as an enveloping stream over the head of the missile With a minimum of turbulence, so that full coverage of the head of the missile by this stream is assured. For that purpose, the wall 26 is made progressively thin as it approaches the tip 22, The gas in the chamber 23 flows under pressure through the porous wall 26 mainly towards its tip and forms a protective gas blanket A (FIG. 2) over the head of the missile, thereby disassociating the high temperature air boundary layer B from contact with the surface of this missile head and at the same time serving as a coolant for the missile head.

After the vaporizable material 24 has been exhausted and the forward end of the secondary nose cone section 15 has been melted off, it is desirable, in accordance with the present invention, to dissipate the high heat from the air boundary layer and to prevent thereby too rapid thermal and abrasive destruction of the remaining part of the secondary nose cone section. For that purpose, the secondary nose cone section 15 is formed with a plenum chamber 35 located behind the chamber 23 and having an outer end wall 36 forming a separating wall between the chambers 23 and 35. This end wall 36 may be formed separately from the main body of the head portion 20 of the secondary nose cone section 15 of sintered material similar to that of said main body, as for example, of stainless steel, and may be later brazed, fused or otherwise united to said main body to form a unit therewith.

The chamber 35 encloses a series of spaced discs 37 and 38 of materials of extremely high fusing temperature, such as carbon, which has a melting point of about 5000" F. Sandwiched between these carbon discs 37 and 38 are cake layers 40 of magnesia also having a high fusing temperature, namely about 5000 F and serving the purpose to be described.

To permit the hot air from the air boundary layer B to enter the plenum chamber 35 and to pass through the carbon discs 37 and 38 and through the layers 40 of magnesia therein, the end wall 36 of this chamber has a series of holes 41 filled with plugs 42 of material of comparatively low fusing temperature, as for example, copper, so that they will melt out of said holes when exposed directly to the action of the air boundary layer. The

carbon discs 37 and 38 also have apertures 43 and the magnesia layers 40 are similarly provided with apertures 44. The apertures 41, 43 and 44 are out of registry to direct air from the boundary layer B tortuously through the elements 36, 37, 38 and 40.

Behind the plenum chamber 35 is an air discharge heat radiating chamber 45 formed in the secondary nose cone section 15 and having the apertures 43 in the end disc 38 as inlets and peripheral holes 46 as outlets. This discharge chamber 45 has a series of heat radiating fins 47 intimately associated with the war head 10, which will be made of magnesium oxide or any of the higher temperature carbides. These fins 47 may extend radially of the chamber 45 or may extend in the form of involutes, as shown in FIG. 5, to assure cooling of the war head 10 by the cooled air passing along said fins, and are integral with the end wall 50 of the skirt portion 21 of the secondary nose cone section 15.

Magnesia decomposes at high temperatures, and since this action is an endothermic one, large amounts of heat are absorbed thereby. The magnesia layers 40 in the plenum chamber 35, therefore lowers to a considerable extent the temperature of a high temperature gas forced therethrough and at the same time is reduced in bulk. The magnesia layers 40 melt at a temperature of about 5000 F. and, therefore, in conjunction with the carbon discs 37 and 38 contribute as a secondary heat sink, absorbing B.t.u.s and controlling dissipation thereof without undesirable destructive thermal action.

The magnesia layers 40 are effective to lower the temperature of the air from the boundary layer B which surges through it after the end of the secondary nose cone section 15 and the copper plugs 42 in the wall 36 have been burned off. At this stage of the missiles descent, the air will course through the magnesia layers 40 in intimate contact therewith and will be cooled thereby before being discharged into the chamber 45. This cooled air passes through the chamber 45 in intimate contact with the heat radiating fins 47 and will discharge from the outlets 45, thereby cooling the war head 10 with which the fins are intimately associated. The air discharged from the outlets 46 flows along the skirt portion 21 of the secondary nose cone section 15 thereby assisting in maintaining the integrity of this skirt portion and in preventing overheating of the war head 10.

The secondary nose cone section 15 is made up of two parts 20 and 21 of the same material, for example, sintered stainless steel, connected together to form a unit, as previously described. To effect connection between these two parts with continuity, the skirt part 21 has a peripheral flange 51 at its forward end and the rear of the part 2%) has a peripheral recess 52 to receive this flange snugly and flush with the contour of said part 20. The two parts 20 and 21 of the secondary nose cone section 15 are fused together, after being separately sintered and shaped.

The sintered parts 20 and 21 are separately formed by molding, compressing and sintering and are then fused together to form a unit. The heat radiating fins 47 may be separately formed of the same material, as for example, sintered stainless steel and then fused onto the end wall 50 of the nose cone portion 21 or may be formed thereon by the same procedure which produces said nose cone portion.

After the nose cone portion 20 is formed as described with a hollow to define the chamber 23 but without the vaporizable material 24 therein and without the end wall 36 fused in position thereon, the material 24 may be inserted in said hollow if it constitutes a solid or may be poured therein through an opening 54 in the wall of said nose cone portion after the end wall 36 has been fused in position, if said material constitutes a liquid or a solid pourable material. This opening 54 may be later plugged after the chamber 23 has been filled.

As another alternative, the nose cone portion 20 may be made separately by sintering into two parts dividing the chamber 23, and these parts may then be fused together into a unit. In that case, the end wall 36 may be formed integrally with one of said parts in the processing of producing said part by sintering.

The nose cone section 20 after being formed as described, is connected to the primary nose cone section 14 to form a unit therewith. Since the nose cone portion 20 and the primary nose cone section 14 are of dissimilar materials, one, for example, being made of sintered copper and the other of sintered stainless steel, it is desirable to connect them together by an operation akin to brazing. For that purpose, a layer of metal, such as tin, copper or nickel is applied to one of the joint surfaces at 16 or 22 of the nose cone portion 21 or the primary nose cone section 14, either by vacuum deposition, painting, electrolytic deposition or spraying, and while the two parts 14 and 20 are snugly and conformably fitted together at 16 and 22, these are heated at around 1700 F. to braze them together into a unit.

After the sintered stainless steel parts 20 and 21 are assembled and fused together with the different elements 24, 37, 33 and 40 incorporated therein, and after the resulting unit is joined to the primary nose cone section 14 as described, the assembled nose cone 13 produced is covered with a layer 56 of highly polished metal, which is stable against oxidation or other chemical action through long storage periods and which, therefore, main tains its high polish during these periods. A noble metal is desirable for that purpose, and platinum is preferred. This platinum layer 56 is preferably applied by electro plating to the surface of the nose cone 13 after said surface has been polished, although it may also be applied by vacuum. The resulting metal layer 56 completely seals the outer surface of the nose cone 13 except for the openings 46', has a permanent and highly polished surface reflecting up to 95% and can withstand high temperatures.

As described, the nose cone 13 serves as a heat sink to draw out heat, but to assure maximum heat sink capacity of the nose cone, there is disposed in back of the secondary nose cone section 15 a sheet 60 of metal of high conductivity and of such length, thickness and shape, as to dissipate effectively the heat generated by the part of the nose cone in closest contact with the air boundary layer. This metal sheet 60 preferably made of sintered copper powder is in the form of a frusto-conical cup tapering towards its end wall and conforming in external shape with the inside of the skirt portion 21 of the secondary nose cone section 15 to nest therein in continuous surface contact therewith and to form a liner therefor. The skirt of the metal cup sheet 60 is sufiiciently longer than the skirt portion 21 of the secondary nose cone section 15 to cause a rim part 61 of said sheet of substantial length to project beyond the end of said skirt portion 21. This assures sufficient material in the metal sheet 60 to receive and dissipate heat effectively and to protect a substantial length of the forepart 11 of the war head 10 against the destructive action of heat.

To shield further the war head 10 against the destructive action of heat, an insulating sheet 63 is interposed between the copper sheet 60 and the war head. This insulating sheet 63 desirably comprises two layers 64 (FIG. 6) of cloth woven from porcelain fibers and separated by a highly reflective metal foil 65 able to withstand high temperatures. The cloth layers 64 are composed of ceramic fibers spun with carrying fibers, such as glass, to form a woven fabric of the desired shape and the fabric is then coronized at 2000 F. to remove the carrying fibers.

The foil 65 is preferably made of noble metal such as platinum and helps in reducing the transmission of heat from the nose cone 13 to the war head 10.

The insulating sheet 63 compositely constructed as described, is in the form of a tapering cup shaped to fit conformably between the forepart 11 of the war head 10 and the inside of the skirt portion 21 of the secondary nose cone section 15.

During upward flight, the speed of the missile is low enough, so that the primary nose cone section 14 remains intact, as shown in FIG. 1, thereby affording the desirable low drag-to-weight ratio. During the downward flight of the missile, certain known aerodynamic and ballistic conditions prevail. A shock front layer is created, which precedes the missile due to the speed and the compressing effect on the surrounding air. Also created close to the nose cone 13 is the highly compressed high temperature air boundary layer B (FIG. 2), which is primarily responsible for the high heating rate generated near the. nose cone 13. Between the boundary layer and the shock front is a shock layer of turbulent air and at the blunt end of the missile formed substantially into hemispherical shape after the cone tip 17 has melted off, there occurs a stagnation point of minimum turbulence.

During downward flight of the missile, the following action takes place: Upon entering the air stratum where the air boundary layer B is produced, the temperature developed by said layer is extremely high. At Mach 8, the temperature would be 6000 F. and at Mach 18, the temperature would be 12,000 F. This temperature would cause the tip 17 on the primary nose cone section including the corresponding part of the platinum layer 56 to melt off, thereby exposing the sintered metal. Heat transmitted during this action through the sintered metal to the vaporizable material 24 will cause this material to expand and turn into gas. This gas and some liquid, if the material 24 is liquid, will be forced out through the pores of the sintered metal and out through the end portion near the stagnation point where the tip 17 and the layer 56 of platinum has been flashed off, producing thereby the protective gas curtain A between the high temperature air boundary layer B and the surface of the nose cone 13, as previously described, and as shown in FIG. 2. This action not only produces a prote'ctive gas curtain A dissassociating the air boundary layer B from intimate contact with the surface of the nose cone 13 but at the same time has a sweat cooling action on the sintered metal, as it passes through the pores thereof.

When it is considered that the material 24 has a high heat of vaporization absorbing large amounts of B.t.u.s when converted from one state into another, without change in temperature, it is seen that the material serves effectively as a heat sink to absorb heat and to prevent thereby excessive heat from reaching the war head 10.

The burning off of the primary nose cone section .14 as described, produces a blunt end at the forepart of the descending missile, thereby increasing the drag-to-weight ratio of the missile, and slowing down its speed, but not sufiiciently to permit it to be easily intercepted. As the missile continues to descend and the forepart of the secondary nose cone section 15 continues to burn ofi, a stage will be reached as shown in FIG. 3, where the material 24 will be all vaporized, and the walls of the chamber 23 burnt off sufiiciently to expose the wall 36 with its copper plugs 42. These plugs will melt, causing the hot air from the boundary layer to course through the holes 41 formed thereby and through the plenum chamber inintimate contact with the magnesia therein, thereby cooling this air. The cooled air passes through the discharge chamber and over the heat radiating fins 47 to carry away the heat from said fins and then flows out through the peripheral openings 46 of the nose cone 13.

Eventually, all of the forepart of the missile shown in the stage of FlG. 3 is burnt oh and in the last stage of downward flight, just before the target is reached, the

missile will be approximately in the condition shown in FIG. 4.

FIG. 7 shows a modified form of nose cone 13a, in which the vaporizable liquid material of FIG. 1 is replaced by a vaporiza'ble solid material 24a of preformed shape. In this modification, the nose cone 13a of FIG. 7 comprises three main sections 70, 71 and 72 secured together to form a unit. The forepart 14a of section 70 constitutes a primary nose cone section similar to the nose cone section 14 in the construction of FIG. 1 and the rear part 73 constitutes a deep flaring skirt defining a chamber 23a in which the vaporizable solid material is housed. This cone section 70 is desirably formed of sintered material corresponding to that employed for the primary cone section 14 in the construction of FIG. 1, as for example, sintered copper.

The middle cone section 71 defines the plenum chamber 3511 corresponding to the plenum chamber 35 in the construction of FIG. 1, to house therein the magnesia layers 40 and the carbon or carbide discs 37 and 38 as in the construction of FIG. 1. This intermediate section 71 is made of material of comparatively high fusing temperature, as for example, sintered stainless steel.

The rear section 72 of the nose cone 13 corresponds to the skirt portion 21 of the nose cone in the construction of FIG. 1 and is similar in shape and of the same material.

The three sections 70, 71 and 72 are keyed together as shown to form a unit presenting a continuous outer contour in its preflight stage and are brazed or fused together into an integral unit.

In the operation of the missile, during its descent, after the cone section 70 has been burnt off, the solid sintered copper mass 24a will be exposed. In the early stages of descent through the air layers, this exposed copper mass 24a will be in semiplastic or soggy state and has a tendency to shell off in large segments or lumps under the abrading action of the air. To maintain the integrity of this sintered copper mass 24a, so that its consumption is gradual, there are embedded therein a series of reinforcing discs 75 made of a material having a high fusing temperature, such as sintered carbon or sintered carbides. These reinforcing discs 75 are stacked and keyed together to form a sustaining core for the sintered copper mass 24a and have spaced respective perforated flanges 76 to assure locking of this mass to the discs.

In all other respects, the construction of FIG. 7 is similar to that of FIG. 1.

In the flight operation of the missile, during the early stages of descent through the air layers, the top of the cone section 70 burns off, exposing the secondary body 24a of sintered copper reinforced by the discs 75 of higher fusing temperature. This exposed secondary body 24a presents a blunt forward end and, therefore, serves to slow down the missiles descent. The high heat developed melts the sintered copper body 24a and vaporizes it. The latent heat of vaporization required for this physical action chills the metal mass, so that it serves as a primary heat sink. At the same time, the vapors generated form a protective gas stream immediately enveloping the forepart of the missile and thereby disassociating the high temperature air boundary layer therefrom.

Since the body 24a of sintered copper is reinforced by the discs 75 of high fusing temperature, this body is sustained against rapid dismemberment by the abrading action of the air.

Eventually, the reinforcing discs 75 will also burn and/ or abrade off, and the missile will reach a stage similar to that shown in FIG. 3. From then on, the nose cone of the missile follows the operational pattern described in connection with the construction of FIGS. 1-4.

In the embodiment of FIG. 8, the construction is similar to that of FIG. 7, except that the foresection 70b of the nose cone 13b has a recess housing therein, a rocket 80 or cluster of rockets located in reversed position and containing a solid fuel. When the tip of the nose cone 13b is burnt oif during the initial stages of the missiles descent through the air layers, the rocket is automatically fired by the heat generated, imparting to the missile a thrust, which slows down its descent, and, therefore, its heating rate. This rocket 80, per se, may be of wellknown type, such as the socalled Jato, which has a solid propellant and which is ordinarily employed for jet assisted take-off.

The rocket not only serves to impart a thrust to the missile opposite to that of gravity, but as the gas from the rocket pours over the nose cone 1312, it forms a protective gas curtain over the forepart of the missile, disassociating the high temperature air boundary layer from the outer surface of the missile.

By directing the stream of vaporized material, which at the high temperatures created during descent isin the form of a gas or vapor around the nose cone periphery, We can attain a further cooling action through the phenomenon of disassociation of this vapor. The vapor at this speed, hitting and passing over the nose cone, breaks down into its component parts which ultimately become charged ions or free radicals. The large amounts of energy required to break down the stable chemical structure of the gaseous molecules thus serve to reduce the temperature of the vapor passing over the missile skin.

The foresection 70b of the nose cone 13b is desirably made of such construction and material, as to vaporize and produce a gas which assists in forming the protective missile enveloping curtain stream. For that purpose, the cone section 70b comprises a series of stacked asbestos fabric sheets 81 impregnated with a vaporizable resin, such as a phenolic resin, and pressed and shaped to form a unit 82 with a recess for the rocket 80. Surrounding this unit is a shell 83 tapering towards a point 84 to provide a low drag-to-weight ratio contour for upward flight, and having a deep flaring skirt 85 defining the chamber 23b. This shell 83 is made up of asbestos fabric sheets 86, wrapped around the unit 82 and impregnated with a vaporizable resin, such as a phenolic resin. The two laminated units 82 and 83 are pressed and fused together and afiord a great deal of structural strength.

The phenolic resin in the cone section 7012 and the water of crystallization contained therein, vaporize, forming the protective gas stream around the forepart of the missile, serving the purpose described.

In all other respects, the nose cone 13b of FIG. 8 is similar to that of FIG. 7 and operates in a similar manner.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto, but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

l. A nose cone for a ballistic missile of the intercontinental type having a head and adapted in its flight to leave and reenter the earths atmosphere, comprising a first member composed of a high melting point metal attached to said head and having a front wall to be exposed to the atmosphere during at least a portion of the descent of said missile after reentry into the atmosphere and forming with said head a first chamber, said front wall having a series of openings containing heat fusible plugs adapted to be melted by the ambient temperature to expose said openings, a solid material capable of vaporizing endothermically without passing through the liquid state disposed in said chamber in the path of the air passing through said openings, and peripheral passages in said member for causing the air after passing in thermal exchange with said material to flow around the outer peripheral surface of said head.

2. A nose cone as set forth in claim I in which said material is carbon.

3. A nose cone as set forth in claim 1 having a second member carried by said first member, said second memher having a second front wall composed of a porous, gas-pervious, sintered metal of. high melting point and spaced in advance of said first member to form therewith a second chamber and to shield said first member from the atmosphere, said second wall being exposed to the atmosphere during at least a portion of the descent of said missle, said second wall being fusible by the ambient temperature to expose said first wall, and a second heat vaporizable material in said second chamber, said second heat vaporizable material forming a vapor under a pressure which passes through said second pervious wall to form a vapor blanket around said nose cone prior to the fusing of said second wall.

4. A nose cone as set forth in claim 3 in which said second heat vaporizable material is a solid material.

5. A nose cone as set forth in claim 3 in which said second heat vaporizable material is magnesia.

6. A nose cone as set forth in claim 3 having a protective member composed of a cone of sintered metal having a melting point lower than said high melting. point 20 metal and attached to and disposed in advance of said second member and shielding said second member from the atmosphere and adapted to be melted and removed during the initial portionof the reentry of said missil to expose said second member.

References Cited in the file of this patent UNITED STATES PATENTS 399,881 Graydon Mar. 19, 1889 608,125 Hurst July 26, 1898 1,376,316 Chilowsky Apr. 26, 1921 1,426,907 Ramsey Aug. 22, 1922 2,011,249 Larson Aug. 13, 1935 2,401,483 Hensel June 4, 1946 2,405,001 Whittaker July 30, 1946 2,409,307 Patch Oct. 15, 1946 2,468,820 Goddard May 3, 1949 2,539,643 Smythe Jan. 30, 1951 2,782,716 Johnston Feb. 26, 1957 2,835,107 Ward May '20, 1958 2,850,978 Franklin Sept. 9, 1958 2,868,500 Boulet Jan. '13, 1959 FOREIGN PATENTS 89,235 Germany Nov. 9, 1896 1938 484,438 Great Britain Mav 5.

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