US 3523483 A
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United States Patent Inventor Hyman Serbin Beverly Hills, California Appl. No. 206,559 Filed June 28, 1962 Patented Aug. 11, 1970 Assignee United States of America as represented by the Secretary of the Air Force SHELTER PIT 9 Claims, 5 Drawing Figs.
U.S. Cl 89/l.8, 89/1.819, 89/36, 98/119,109/1 Int. Cl F41f3/04 Field of Search 89/ l .7 l 3;
89/36;109/49.5, 58.5, 1; 98/58, 59, 1 19, 79; 89/36, 1.7;98/58, 59, 119, lARS; 110/184; 7 138/37  References Cited UNITED sTATEs PATENTs 2,871,802 2/1959 Fishler 89/36X 2,981,152 4/1961 Milleretal 39/1,7(B)X FOREIGN PATENTS 1 136,252 12/1919 GreatBritain.
OTHER REFERENCES Aviation Week and Space Technology, Jan. 1, 1962, page 2 I Minuteman Launch Silo Details.
Primary Examiner- Samuel W. Engle Atr0rneyWade Koontz and Ruth G. Codier ABSTRACT: This invention relates to a choke-type shelter pit and, more particularly, to a chamber located below ground, and so designed as to protect equipment housed therein from damage due to shocks originating above ground, a particular application being the construction and design of missile launching pits.
Patented Aug. 11, 1970 Sheet 1 of5 I N V EN TOR.
.semsm/ f/YMl/V 11 (Law Patented Aug. 11, 1970 Sheet INVENTOR. HYMA/V SAE/EB/N Arron/It) SHELTER PIT The purpose of the present invention is the construction of underground shelter chambers such as missile launching pits and other installations located below ground, which are designed to withstand very high shock pressures of the order produced by a one megaton nuclear bomb, the missile or other equipment housed in the pit remaining undamaged by the shock and capable of retaliatory measures.
An important feature of the proposed structure is the absence of a door or other closure, so that complicated and time consuming apparatus for opening and closing such doors has been eliminated. The embodiment of the invention here shown is a vertically stacked three-section underground pit having a restricted opening at ground level, a choke area directly underneath where choking action is developed and where the shock pressure sustained at ground level is sufficiently reduced so that equipment housed in the shelter section located below the choke section is undamaged. If the equipment is a missile, it is capable of being kept in readiness for retaliatory launching after the shock has been sustained, the absence of doors permitting quick firing.
The third section, located below the shelter section is of sufficient depth to delay the wave reflected from the floor of the pit until the initial impact has deteriorated. This section may be called the shock reverberation section. Its function is to allow the downgoing shock a sufficiently long time before it is reflected and returned to the shelter section. It also provides damping to the shock wave as a result of viscous motion along the wall. Mufflers or baffles along the wall will accentuate damping.
The principal of the invention is based on the properties of gas flow and the attenuation of pressures of gases passing through a series of restricted openings of increasing size. This reduction in shock pressure is accomplished by causing the shock wave or waves to pass through a chamber or channel located between two or more restricted throats, increasing in diameter, so that at each throat, although the mass rate of flow through each is the same, the effective pressure is reduced and the wave has the appearance of having come from a reservoir at lower than actual pressure. In the description of the present invention, this chamber is called the choke section. If it is relatively long and straight, the shock wave, under usual shock conditions, is normal to the wall and would lie horizontally. The presence of a retarded shock in the choke section may therefore be regarded as due to the sequence of two restricted throats, one above, and one below, and of increasing diameter.
In carrying out the principle in the practical embodiment of the invention, the first throat is located at ground level, and a choke chamber is located between the equipment to be protected, and the ground level opening. As the shock wave proceeds downward, it will be reflected when it reaches the floor or extremity of the chamber installation. The pressure would then reach a value equaling that of the outside conditions creating the shock. It is supposed, however, that the ground level opening is subjected abruptly to a high pressure which rapidly decays. The length of the whole installation is calculated to be so large that the externally applied pressure will have decayed before the reflected shock wave has returned to the lower throat of the choke section. The design of the shelter must be based on the most severe conditions that can be anticipated. The environment considered is a pressure pulse which passes over the mouth opening, and retains its intensity the whole distance between its head" and tail. This idealization is more severe than the actual conditions of a shock wave produced by a blast, where the pressure is high behind the head, and decays continuously to zero.
This invention provides, therefore, a shelter area, not completely closed to the pressure pulse, in which the shock over-pressure becomes only a small part of the overpressure in the incident pulse. The successive sections are of sufficient length and of such construction that the reflected pulse does not arrive at the sheltered and protected area until the tail of the pulse has passed completely over the opening.
In the drawings: FIGURE 1 is a fragmentary schematic cross-sectional view of a launching pit, embodying the invention;
FIGURE 2 is a schematic cross-sectional view of the launching pit, showing its entire depth;
FIGURE 3 is a fragmentary schematic view of the device similar to FIGURE 1, showing addition of a pair of vertically disposed retractable clam shell shields;
FIGURE 4 is a fragmentary cross-sectional and schematic view of the pit showing the travel of the shock wave; and
FIGURE 5 shows a dispersal in an upward movement of a missile s own exhaust along the walls of the pit.
Referring more in detail to the drawings, the launching pit indicated by the numeral is located entirely below ground and is formed of reinforced concrete or such material as is found adequate. Its mouth opening, indicated by the arrow 12, is located at the ground level, and is uncovered. A closure and operating apparatus therefore are dispensed with.
The shelter or launching pit 10 consists essentially of three parts-a choke section 14 whose orifice 12, as noted, is flush with the ground; a shelter section 16 for housing equipment such as the missile 20, and a shock section indicated by the numeral 18. The missile 20, housed in the section 16, is supported in any fashion found expedient and effective, such as trestle 22 shown schematically in FIGURE 3. Clam shell shields 24 may also be used for protection of the missile or equipment and may be movable in and out of protective position as indicated in dotted lines in FIGURE 3, or retracted into the wall of the pit by means (not shown). Neither the missile, the trestle or the clam shell shields form part of the present invention, but are merely adjuncts to it. The shock section may or may not, as found desirable, be provided with baffles 30.
When pit dimensions are discussed, it must be noted, however, that the given dimensions are calculated for an empty pit, and whatever space is occupied by equipment, equipment supporting structure, etc., must be compensated for by an increase in the given dimensions.
The unique manner in which the missile or other equipment housed in the section 16 is protected from shock forces, arising from above-ground blasts, is based on the air flow characteristics within the pit, these characteristics being determined by the design of the pit.
The environment considered is a pressure pulse caused by an above ground blast which passes horizontally over the ground surface and enters the mouth 12. At the head of the pulse, the pressure will be extremely high, decaying continuously to zero. In the device of the invention a chamber is created wherein, at some point, the overpressure will have been reduced to a small portion of the force of the incident pulse. In the case of a missile, the pressure and heat loads will be those encountered in missile flight, which the missile is built to withstand. This point is located in the area within the shelter chamber 16 where the equipment is located. It will be noted that the choke section 14 and two restricted openings 12 and 25, one larger than the other, are interposed between the shelter area and the blast area above ground.
The function of the shock reverberation section, as pointed out above, is to provide time delay before the reflected shock is returned to the shelter section, and to dampen the force of the shock. Baffles 30 noted above augment this effect.
Relative dimensions, as given below, were worked out for a standard ICBM missile, and are of two kinds, essential dimensional relationships which must be preserved in order for the device to operate, and assumed dimensional relationships which may be adjusted experimentally to get optimum results.
Essential dimensional relationships for an environment involving a l Megaton bomb with a 100 psi overpressure is as follows: 70
where D =diameter of missile, D the diameter of ground level the choke section and the shelter area or missile section and L is the length of the shock section I8.
It will be seen that the opening D is larger than the opening D. in the ratio of] to 1.7.
The typical dimensions which may vary are:
61 substantially equal to 02 an angle of the order of45 P= 100 psi L=75 ft D= l6 ft L =30O ft (18.75D)
and the calculated overpressure in the missile section is 16 psi above original air pressure. lt will be observed that the diameters of the shock and choke sections are substantially equal. An example of the operation of the device is as follows:
FIGURE 4 shows an example of the travel pattern of a shock wave of the order of 100 psi. After a time interval of 0.07 seconds from the instant of passage of the shock wave across the orifice 12, the shock pattern within the launching pit appears as shown in FIGURE 4. A stationary shock remains in the position shown at 40. A moving shock wave, 42, 42' FIGURE 4, travels downwardly into the missile housing chamber and at .07 seconds after the bomb shock of 7.7 atmospheres strikes the mouth of the pit, the moving shock has been attenuated to 2.1 atmospheres and is in the approximate position indicated by the line 42 in FIGURE 4 and is still moving downward. At .25 seconds the shock wave, still at 2.1 atmospheres has reached the position 42'0f FIGURE 4.
Launching from underground requires suitable disposition of the exhaust gases. It has been proposed to duct the exhaust away from the site, venting the gases at the ground. Doors or valves would be necessary to prevent back pressures travelling back into the missile section. To obviate this necessity, the pit has been designated with an enlargement of the missile section at its base forming a cavity 44 to receive the initial exhaust and direct it along the wall of the missile chamber as shown schematically in FIGURE 5.
Although the invention has been described with reference to particular embodiments it will be understood to those skilled in the art that the invention is capable ofa variety of alternative embodiments within the spirit and scope of the appended claims.
1. A device for housing and launching missiles from underground and for protecting said missiles from blast forces and over pressures originating above ground, said device comprising a chamber for housing said missiles, a system for attenuating shock over pressures entering said chamber, said system comprising a choke section for channeling said over pressures, a plurality of restricted throats in said choke section and located above said chamber, one such throat being located at ground level, said throats being successively less restricted as the blast proceeds downward from ground level to chamber level, so that the over pressure of said blast is lessened in successive stages, reaching an undestructive level as it reaches said chamber.
2. A device for providing an underground shelter for missile launching and for protection of equipment against damage from blast pressures originating above ground, said device comprising a shelter chamber, means for admitting blast over pressures originating above ground to said shelter chamber in attenuated and modified form, said means comprising, a
choke chamber located above said shelter chamber, said choke chamber forming a column above said shelter chamber, at least two restricted throats of graded size in said choke chamber, the smallest of said throats opening to ground surface, the largest of said throats opening to said shelter chamber.
3. An underground missile launching pit for protecting a missile housed therein from blast over pressures originating above ground, and maintaining said missile in condition for retaliatory measures, said pit comprising three communicating sections a choke section, a missile housing section, and a shock reverberation section located vertically and below each other in the order named, a restricted mouth orifice on said choke section located at ground level, the wall of said choke section diverging downwardly to a diameter approximately twice the width of said mouth opening and proceeding downwardly to a depth approximately equal to its largest diameter, a restricted area at the lower end of said choke section defining also the upper end of said missile housing section, and having a diameter larger than the diameter of said ground level orifice.
4. A device as claimed in Claim 3 wherein said shock reverberation section is of a length substantially four times the length of said missile.
5. A device as claimed in Claim 3 wherein the diameter of the upper throat is substantially twice the diameter of said missile.
6. In a device as claimed in Claim 3, baffle members located in said shock reverberation chamber for damping the shock force of a shock wave entering said shock reverberation chamber.
7. An underground missile launching pit comprising a missile launching section capable of housing a missile, a shock section located below said missile housing section and communicating therewith, said shock section being of relatively large depth and of constant diameter, said diameter being less than the diameter of said missile launching pit, a choke section located above said missile launching pit, and upper restricted throat on said choke section provided with an uncovered mouth opening located at ground level, a lower throat forming an opening on said choke section communicating with said missile launching section, and having a substantially larger diameter than the diameter of said upper restricted throat.
8. In an underground missile launching pit a choke section, a missile housing section and a shock section, located one below the other in the order named, a restricted throat in said choke section located at ground level, said choke section wall curving from said throat to a cross-sectional diameter of approximately twice the diameter of said restricted throat, a restricted throat forming a lower orifice on said choke section and leading downwardly into said missile housing section, said shock section being located below and communicating with said missile housing section, said lower restricted throat being of a diameter greater than the diameter of the ground level opening so that a shock induced flow through each successive restricted throat will have modified and dampered characteristics, proceeding into the missile housing section at a reduced rate and under reduced pressure.
9. A device for providing a blast protected underground shelter comprising a shelter chamber, means for admitting blast over pressures originating above ground to said shelter chamber in attenuated and modified form, said means comprising, a choke chamber located vertically above said shelter chamber, said choke chamber forming a column above said shelter chamber, at least two restricted throats of graded size in said choke chamber, the smallest of said throats opening to ground surface, the largest of said throats opening to said shelter chamber.