Vacuum insulated warhead

Abstract

A vacuum insulation layer is wrapped around the length of a warhead to thermally insulate the warhead from fire or aerodynamic heating. The vacuum insulation layer may be integrally formed into the warhead casing or provided as a sleeve that may be permanently or removably positioned about the warhead casing. The vacuum insulation layer is held under vacuum with a pressure of less than 25 Torr and a thermal conductivity Tcond_vac of less than one-third of the thermal conductivity of air Tcond_air.

Claims

1. A warhead, comprising: an explosive material positioned inside a warhead casing; and a vacuum insulated casing including inner and outer walls defining an annular void space around a length of the warhead casing and explosive material, wherein the annular void space is held under vacuum with a pressure of less than 25 Torr and a thermal conductivity Tcond_vac of less than one-third of the thermal conductivity of air Tcond_air to form a vacuum insulation layer around the length of the warhead casing and explosive material.

2. The warhead of claim 1, wherein the pressure in the void space is a medium vacuum between 25 Torr and 10.sup.3 Torr.

3. The warhead of claim 1, wherein the pressure in the void space is a high vacuum between 10.sup.3 Torr and 10.sup.6 Torr.

4. The warhead of claim 1, wherein Tcond_vac is less than one-fifth Tcond_air.

5. The warhead of claim 1, wherein Tcond_vac is approximately 1/6.6 that of Tcond_air.

6. The warhead of claim 1, wherein the warhead casing is formed of a metal material and the inner and outer walls are integrally formed with the warhead casing.

7. The warhead of claim 1, wherein the inner and outer walls are formed as a sleeve that fits over the warhead casing.

8. The warhead of claim 7, wherein the warhead casing wall is formed of a composite material.

9. The warhead of claim 7, wherein the sleeve is permanently affixed to the warhead casing.

10. The warhead of claim 7, wherein the sleeve is removable.

11. The warhead of claim 1, wherein the warhead casing is formed of a metal material that forms a fragmentation layer, which upon detonation of the explosive material fragments with the outer wall to form a fragmentation pattern.

12. A warhead, comprising: an explosive material; and an integrally formed vacuum insulated metal warhead casing including an inner wall around a length of the explosive that forms a fragmentation layer and an outer wall that defines an annular void space, wherein the annular void space is held under vacuum with a pressure of less than 25 Torr and a thermal conductivity Tcond_vac of less than one-third of the thermal conductivity of air Tcond_air to form a vacuum insulation layer around the length of the warhead casing and explosive material.

13. The warhead of claim 12, wherein the pressure in the void space is a medium vacuum between 25 Torr and 10.sup.3 Torr.

14. The warhead of claim 12, wherein the pressure in the void space is a high vacuum between 10.sup.3 Torr and 10.sup.6 Torr.

15. The warhead of claim 12, wherein Tcond_vac is less than one-fifth Tcond_air.

16. The warhead of claim 12, wherein upon detonation of the explosive material the fragmentation layer and outer wall fragment to form a fragmentation pattern.

17. A warhead, comprising: an explosive material positioned inside a warhead casing; and a sleeve including inner and outer walls defining an annular void space that slides around the warhead casing and explosive material, wherein the annular void space is held under vacuum with a pressure of less than 25 Torr and a thermal conductivity Tcond_vac of less than one-third of the thermal conductivity of air Tcond_air to form a vacuum insulation layer around a length of the warhead casing and explosive material.

18. The warhead of claim 17, wherein the warhead casing wall is formed of a composite material.

19. The warhead of claim 17, wherein the sleeve is permanently affixed to the warhead casing.

20. The warhead of claim 17, wherein the sleeve is removable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A-1B, as described above, are sectional and end views of an insulated warhead positioned inside an airframe of the weapon system;

(2) FIGS. 2A-2B are sectional and end views of an embodiment of a vacuum insulated warhead positioned inside an airframe of the weapon system;

(3) FIGS. 3A and 3B are a Table and plot of the relative thermal conductivity of a vacuum to air for low, medium and high vacuum;

(4) FIGS. 4A-4C are drawings depicting the effects on a warhead fragmentation pattern of different insulating techniques;

(5) FIG. 5 is a drawing in which the vacuum insulation layer is integrated into the warhead casing; and

(6) FIG. 6 is a drawing in which the vacuum insulation layer is provided as a sleeve that is either permanently or removably fitted over the warhead casing.

DETAILED DESCRIPTION

(7) In the present disclosure, a vacuum insulation layer is wrapped around the length of a warhead to thermally insulate the warhead from fire or aerodynamic heating. The vacuum insulation layer may be integrally formed into the warhead casing or provided as a sleeve that may be permanently or removably positioned about the warhead casing. The vacuum insulation layer is held under vacuum with a pressure of less than 25 Torr (assuming storage or operation of the warhead at sea level with a temperature of 25 degrees C.) and a thermal conductivity Tcond_vac of less than one-third of the thermal conductivity of air Tcond_air. In different configurations, the vacuum insulation layer may reduce weight or volume occupied by the requisite thermal insulation. If the warhead produces a fragmentation pattern, the vacuum insulation layer has negligible impact on the fragmentation pattern or velocity of the fragments.

(8) As shown in FIGS. 2A-2B, an embodiment of an insulated warhead 200 includes a warhead 202 in which an explosive material 204 is positioned inside a warhead casing 206 and a vacuum insulation layer 208 wrapped around a length of warhead 202.

(9) A vacuum insulated casing 210 including inner and outer walls 212 and 214 defines an annular void space 216 around a length of the warhead casing 206 and explosive material 204. The annular void space 216 is sealed and held under vacuum with a pressure of less than 25 Torr (assuming storage or operation of the warhead at sea level with a temperature of 25 degrees C.) and a thermal conductivity Tcond_vac of less than one-third of the thermal conductivity of air Tcond_air to form vacuum insulation layer 208.

(10) In different embodiments, the vacuum may be a medium vacuum between 25 Torr and 10.sup.3 Torr or a high vacuum between 10.sup.3 Torr and 10.sup.6 Torr. A higher vacuum (lower pressure) corresponds to less particles (contaminants) in the vacuum and thus a lower thermal conductivity. Tcond_vac may be less than one-fifth the Tcond_air and reach a limit of approximately 6.6 less than air. Vacuum insulation layer 208 can provide equivalent or better thermal insulation than the insulation layer (air gap/conductive layer/air gap) 114 shown in FIGS. 1A-1B with a far thinner layer. This may both reduce weight and occupied volume for the insulated warhead. As shown in FIG. 2A, when positioned within an air frame the requisite air gap 218 between the warhead 202 and airframe skin 220 need only be large enough for physical tolerances. The air gap 218 does not meaningfully contribute to the thermal insulation.

(11) As will be discussed later, the vacuum insulation layer 208 may be integrally formed into the warhead casing 206 or provided as a sleeve that may be permanently or removably positioned about the warhead casing 206. For example, the sleeve may be used to provide thermal insulation and protection from fires during storage of certain warheads but removed when the warhead is assembled with the air frame or loaded in a launch system. The sleeve, which is formed from a material such as metal suitable to hold vacuum for long periods of time, may be used with a warhead casing of the same material or a different material such as in the case of a composite casing.

(12) Referring now to Table 300 of FIG. 3A and a plot 302 of the relative thermal conductivity of a vacuum to air in FIG. 3B, at sea level and a temperature of 25 C, air has a thermal conductivity of approximately 0.026 W/mK, aluminum of approximately 1.9 W/mK and a high vacuum of approximately 0.004 W/mK. As defined herein, a low vacuum is between 760 Torr (1 atm) and 25 (Torr), a medium vacuum between 25 Torr and 10.sup.3 Torr or a high vacuum between 10.sup.3 Torr and 10.sup.6 Torr. Under low vacuum the difference in thermal conductivity with air is insufficient to provide the requisite thermal insulating benefits given the requirement to form and hold a vacuum. At medium and high vacuum, the thermal conductivity of the vacuum is less than 1/3, preferably less than 1/5 and ideally approximately 1/6.6 that of air. This provides a substantial thermal insulating benefit over an air gap or an insulating layer formed as an air gap/conductive layer/air gap.

(13) FIGS. 4A-4C illustrate a fragmentation pattern 400 for a fragmentation warhead 402 and the possible degradation of the fragmentation pattern in both the desired pattern and fragment velocity attendant to the different techniques for thermally insulating warhead 402. In this example, detonation of warhead 402 throws fragments 404 radially into a conic fragmentation pattern 400 at a desired fragment velocity. Any distortion of the pattern or slowing of the fragments is undesired.

(14) Although not illustrated here, the layers of ablative (insulating material) and a protective intumescent coating formed in relieved areas of the warhead coating described in U.S. Pat. No. 3,992,997 will, upon detonation, tend to rip and tear and stick to fragments 404 thereby distorting the fragment pattern and reducing the velocity of the fragments.

(15) As shown in FIG. 4B, the use of an insulating layer 410 formed as an air gap/conductive layer 412/air gap around warhead 402 will also degrade the fragment pattern and reduce fragment velocities. Upon detonation, conductive layer 412 will maintain physical integrity long enough to redirect and slow fragments 404.

(16) As shown in FIG. 4C, the use of a vacuum insulating layer 420 around warhead 402 has minimal impact on fragmentation pattern 400. Upon detonation, the vacuum insulating layer 420 collapses and creates fragments that do not impact the fragmentation pattern 400.

(17) As shown in FIG. 5, a vacuum insulating layer 500 is integrally formed in a warhead casing 502 that contains explosive 504. Warhead casing 502 must be formed of a material, typically metals such as titanium, steel or aluminum, on which sufficient vacuum can be pulled and sustained for the life of the warhead, or at least until the warheads are inspected and maintained.

(18) As shown in FIG. 6, a vacuum insulating layer 600 is integrally formed in a sleeve 602, which fits over the warhead casing 604 that contains explosive 606 to form a warhead 608. Sleeve 602 may be permanently or removably positioned about the warhead casing 604. For example, the sleeve may be used to provide thermal insulation and protection from fires during storage of certain warheads but removed when the warhead is assembled with the air frame or loaded in a launch system. Or the sleeve may be positioned over warhead 608 and then assembled into an airframe. The sleeve 602, which is formed from a material such as metal suitable to hold vacuum for long periods of time, may be used with a warhead casing of the same material or a different material such as in the case of a composite casing.

(19) While several illustrative embodiments of the disclosure have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the disclosure as defined in the appended claims.