Jettisonable protective cover device

An in-flight jettisonable protective cover device for protecting fragile, accurate, radomes or signal-responsive components for the major portion of a flight which is capable of being jettisoned in one piece at supersonic speeds from a guided missile, other air vehicles, or space vehicles. The cover device is for use, for example, in combination with a guided missile having a shell structure, a nose portion, and a radome in the missile nose. The cover device is attached to the missile nose for covering the radome such that an inner space is defined. A plurality of shear pins or other quick-release mechanisms attach and retain the cover device to the missile shell. A source of low pressure gas pressurizes the inner space to approximately 50 psi. A rapid-discharging, high pressure gas cartridge produces a high pressure gas for exerting a pressure force on the aft face of the cover device. The pressure forces are sufficient to shear the retaining pins and accelerate the cover device sufficiently forward to clear the missile body at supersonic speeds. The missile angle of attack creates lateral aerodynamic forces on the cover deivce to clear it from the missile. The sensitive radome can then be used for high precision detection and tracking as required at intercept.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to a protective covering for radomes or 
uncovered signal-responsive components which are integral with air or 
space vehicles and more specifically, involves a cover device which may be 
jettisoned during supersonic flight. 
2. Background of the Invention 
For aerodynamic reasons it is desirable to have a pointed nose on a guided 
missile and other flight vehicles. However, and by way of example, it has 
been found that guided missiles utilizing an antenna looking through a 
pointed radome experience error slope. Small radome error slopes at launch 
or for mid-course guidance may not be critical. However, error slope is 
particularly harmful when high precision is required such as at intercept. 
This is particularly true with high altitude performance of radio frequency 
guided missiles. 
A highly functional radome, i.e. one that is radiation transparent, would 
be a thin, hemispherical dome of glass or similar material. However, such 
a radome provides high drag. Additionally, the radome is subject to rain 
erosion, insect impingement, rocket or turbojet motor exhaust, optical 
contamination, ice formation, general debris, humidity, heat, salt, sand, 
dust and the like. Also, the radome is subject to general physical damage 
during transportation, storage, loading, and firing. 
Therefore, it is desirable to have an aerodynamic protective cover device 
for radomes or signal-responsive components which is suitable for launch 
and for mid-course guidance, and which is jettisonable when high precision 
is required at intercept. 
It is further desirable that such a protective cover device be jettisonable 
in such a manner that the vehicle and radome or signal-responsive 
components are not damaged. 
SUMMARY OF THE INVENTION 
This invention is a jettisonable protective cover device in combination 
with a guided missile, in this example, having either a radome or 
uncovered signal-responsive components in the missile nose. The 
jettisonable cover device, for example, generally comprises a generally 
ogive-shaped structure capable of separating in one piece from the missile 
during supersonic flight. The cover device attaches to the forward section 
of the missile and covers the exemplary radome such that an inner space is 
defined. A plurality of shear pins attach the aft end of the cover device 
to the missile shell. Various other quick-release mechanisms can be used 
in place of the shear pins. A low pressure gas source is valved to 
pressurize the inner space to approximately 50 psi. A high pressure gas 
source furnishes high pressure gas to a cavity adjacent the aft end of the 
cover device. In response to a signal, the high pressure gas source 
provides gas to the cavity at approximately 2000 psi. This pressure force 
on the aft flange face is sufficient to shear the plurality of shear pins 
(in this example) and accelerate the cover device forward. The force from 
the pressurized inner inter-dome gas continues this acceleration and 
escapes out the aft opening. Lateral aerodynamic force is created by a 
slight pitching movement or angle of attack, to accelerate the cover 
device laterally in relation to the missile. These lateral aerodynamic 
forces will produce a lateral displacement sufficient for the jettisoned 
cover device to safely clear the missile before drag and return it to the 
missile. 
Other features and many attendant advantages of the invention will become 
more apparent upon a reading of the following detailed description 
together with the drawings, wherein like reference numerals refer to like 
parts throughout.

DETAILED DESCRIPTION OF THE INVENTION 
With reference now to the drawing and more particularly to FIG. 1 thereof, 
there is shown the forward section of a guided missile, shown generally as 
10, having a nose portion 12. A cover device 20 of the present invention is 
shown in this example as an ogive-shaped structure which is attached as an 
integral part of the missile 10. The position of an exemplary missile 
radome 16 is shown in phantom lines In most applications, the cover device 
20 and the radome 16 would be transparent to electromagnetic radiation. 
Depending upon the desired utilization, the cover device 20 could be made 
of such materials as ceramic, fused silica, fiberglass, pyroceram or 
various metals and alloys or mixtures thereof. Radomes, such as radome 16, 
may be made from ceramic, fused silica, fiberglass or pyroceram materials 
which are fabricated having dielectric qualities which make the material 
transparent to radio-frequency energy. An infrared dome or the like can be 
substituted for, or integrated with, the radome 16. Infrared domes may be 
manufactured from materials such as sapphire, germanium, silicon, quartz 
or calcium aluminate; such materials being transparent to infrared 
radiation. For some uses, such as in the vacuum of space, for example, a 
radome may not be utilized to shield signal-responsive components such as 
a radio frequency antenna, an infrared seeker, an environmental survey 
system, a solar cell device, or a laser device, for example. In such 
cases, an inner-space would be created between the cover device and the 
signal-responsive component(s) which would be sealed from the rest of the 
vehicle. 
As best seen in FIG. 5, cover device 20 has a general nose-cone 
configuration with a generally pointed front end 22, open aft end 24, and 
inner and outer surfaces 27, 28. Rearwardly extending aft flange 25 on aft 
end 24 terminates in face 26. Shear pin bore 29 through aft flange 25 is 
used to secure the cover device 20 to the missile 10. 
FIG. 2 is a view similar to FIG. 1 showing the jettison action of the cover 
device 20 from the missile 10. As will later be explained more fully, the 
gasses jettison the cover device from missile 10. An exemplary trajectory 
for cover device 20 is illustrated as 20a, with arrow "X" depicting the 
pitching moment factors and arrow "Y" illustrating the side of lateral 
load. 
With reference now to FIG. 3, there is shown an enlarged side view, 
partially cut away, of the connecting section of cover device 20 with the 
missile 10 and the jettison mechanism. Missile 10 includes shell structure 
11 defining a forward facing annular cavity 14 for accepting aft flange 25. 
Aft flange 25 is inserted in the cavity 14 leaving a rear portion of the 
cavity 14 unoccupied. Retaining means, such as a plurality of shear pins 
30, pass through shell 11 and attach and retain cover device 20 to missile 
10. A high pressure gas source, such as a gas generator cartridge 40, is 
connected to the high pressure cavity 14. Cartridge 40, when actuated by 
well-known solenoid means (not shown) or pyrotechnic means (not shown), 
for example, generates high pressure gas which is vented to cavity 14. 
Sealing means, such as outer O-ring 32 and inner O-ring 34 seal high 
pressure cavity 14 and prevent high pressure gasses from escaping past aft 
flange 25. A low pressure gas source, such as cylinder 50, provides gas for 
pressurizing an inner space 18. Cylinder 50 may be actuated by well-known 
solenoid means or pyrotechnic means (neither shown), for example. To 
conserve space, cylinder 50 contains gas at much higher pressure than the 
desired end pressure in the inner space 18. Valve 51 releases the pressure 
from cylinder 50 to a regulator 53 which regulates the gas to the desired 
end pressure and low pressure line 52 delivers low pressure gas to the 
inner space 18. 
FIG. 4 illustrates the initial stage for ejecting the cover device 20 
during flight. To effectively jettison the cover device from missile 10, 
sufficient forward energy must be imparted to the cover device to overcome 
the wind drag forces to move the cover device forward clear of the radome 
16. Lateral forces on outer cover device 20 must then create a trajectory 
causing the cover device to clear all missile appendages. 
As seen in FIGS. 3 and 4, the forward forces are provided by a low pressure 
source, cylinder 50, for pressurizing the inner space 18, and a high 
pressure source 40 for pressurizing high pressure cavity 14. Regulator 50 
lowers the gas pressure from the low pressure source 50 to the desired 
end-pressure in the inner space 18. Thus, the gasses exert two forces on 
cover device 20 relative to missile 10. The first force from the 
pressurized volume is equal to the pressure multiplied by the 
cross-section area of cover device 20. A pressure of 50 psi has been found 
to be sufficient for this purpose. This pressure is not sufficient to shear 
pins 30 or to damage radome 16. Therefore, timing is also not a major 
problem in this regard, and the inner space 18 may be pressurized 
relatively slowly. The second forward force on cover device 20 is provided 
by the high pressure gas introduced into cavity 14 from cartridge 40. The 
second forward force is equal to the pressure of high pressure gas in 
cavity 14 multiplied by the area of face 26. These forces are sufficient 
to shear the plurality of shear pins 30 retaining the cover device 20 to 
the missile. Cartridge 40 is designed to very quickly pressurize cavity 14 
to achieve the high pressure force. Therefore, immediately upon release of 
the high pressure gas from cartridge 40, pins 30 shear and the cover 
device 20 is accelerated forward and separates from missile 10 as shown in 
FIG. 6. Once rear flange 25 is clear of cavity 14, the relatively small 
volume of high pressure gas bleeds off the larger volume of low pressure 
gas in space 18 continuing the acceleration of cover device 20. The gas 
exits out the aft opening, also providing acceleration. 
Once the cover device has passed forward clear of the radome 16, lateral 
wind forces provide a trajectory for clearing all parts of the missile. 
The lateral wind forces may be produced by a pitch rate or angle of attack 
of the missile. To achieve this, the missile is maneuvered so that it is 
developing the desired number of G's. A small angle of attack of 
approximately 2 degrees or larger has been found to be sufficient to 
provide adequate lateral aerodynamic forces to clear the jettisoned cover 
device 20 clear of missile 10. 
A series of eleven tests were conducted in a supersonic wind tunnel with 
full scale models. Velocities of Mach 3.8 to 4.6, inter-dome pressure of 
25 to 50 psi, and pitch angle of 2 to 8 degrees were used. The test 
demonstrated successful separation trajectory of the cover device 20 at 
supersonic speeds and indicated that the cover device would clear all 
parts of the missile including dorsals, tails, etc., during its separation 
trajectory. 
From the foregoing description it is seen that the present invention 
provides many advantages over the prior art. 
A major advantage of the present invention is the substantial reduction in 
missile total drag for the major portion of the flight. 
Another major advantage includes the ability for onboard cooling of a 
radome and/or signal-responsive components. This can be provided by 
circulating cooling gas or liquid between the dome and the low drag nose. 
The cover device can be constructed of quite strong material to protect 
the radome and/or signal-responsive components and shield them from such 
forces as aerodynamic heating, rain erosion, insect impingement, rocket or 
turbojet motor exhaust, optical contamination, ice formation, general 
debris, humidity, heat, salt, sand, dust and the like encountered during 
flight and from general damage during shipping, storage, and handling. 
During flight the cover device 20 will protect the fragile radome and/or 
signal-responsive components from aerodynamic heating and large drag loads 
when the missile is operating a high velocity, high dynamic pressure, and 
high maneuverability. 
The foregoing is a complete description of an exemplary embodiment of a 
jettisonable protective cover device which is constructed with the 
principles of this invention. It is likely that changes and modifications 
will occur to those skilled in the art which are within the inventive 
concepts disclosed or claimed herein. Accordingly, the present invention 
is to be construed as limited only by the spirit and scope of the appended 
claims.