Aeronautics and astronautics – Missile stabilization or trajectory control – Automatic guidance
Reexamination Certificate
1999-07-26
2001-08-14
Gregory, Bernarr E. (Department: 3662)
Aeronautics and astronautics
Missile stabilization or trajectory control
Automatic guidance
C244S003190, C343S705000, C343S872000
Reexamination Certificate
active
06273362
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a window for use in a supersonic or hypersonic target-tracking missile, the window being transparent to electromagnetic radiation.
Supersonic and hypersonic target-tracking missiles are provided with a seeker head having a seeker responding to electromagnetic radiation. The seeker head detects e.g. the infrared radiation from a target object. When the missile is flying at supersonic or hypersonic speed, the structure of the missile is heated up very strongly due to aerokinetic heating-up. High mechanical and thermal loads occur in the missile and the seeker head. Due to the temperature gradients caused thereby, internal stresses are generated to an extent near the breaking point of the material. Furthermore, extremely high impact pressures act on the structure at high air speeds.
The seeker is protected by a window, which is transparent to the relevant electromagnetic radiation.
There are only very few materials which are transparent to infrared radiation and have mechanical properties sufficient for supersonic and hypersonic speeds. Known electromagnetically transparent windows for supersonic and hypersonic target-tracking missiles are made either of magnesium fluoride, zinc sulfide, sapphire or diamond. Furthermore, depending on the requirement, the windows can have different shapes and thickness. For example, it is tried to increase the thickness of the window in order to counteract the thermal loads by increasing the heat capacity.
Windows made of magnesium fluoride or zinc sulfide have a relatively low thermal conductivity and, thus, they are heated up very much during the flying phase, which lead to melting of the outer surface of the window. Furthermore, the seeker can become “blind” due to the self-emission of the window.
When the windows are made of infrared-transparent materials sensitive to brittle fracture, a larger thickness of the window is favorable for taking up the pressure load. On the other hand, thinner windows have favorable properties with regard to thermal shock loads. There exist an optimum window thickness, for which the stresses of the window caused by impact pressure and temperature are minimal.
All known windows transparent to electromagnetic radiation and used in supersonic and hypersonic target-tracking missiles have the disadvantage that they resist the thermal and mechanical loads during the flying phase just for a short time of 1-2 seconds. Normally, however, the actual time of flight is much longer. Up to now this problem is solved in that the window is protected by a solid protective covering during the first flying phase. Thus, during this flying phase, the seeker is covered and target-tracking is not possible. Not until the final flying phase, when the missile already is close to the target, the protective covering is thrown off, which enables the actual target-tracking by the seeker. Such a protective covering is described in German Patent Application No. 37 15 085. Apart from the limitation of the time of target-tracking, the use of such a protective covering is of rather complex design.
European Patent Application No. 0 599 035 discloses a connecting arrangement for connecting a dome, which covers a seeker head and is made of relatively brittle infrared-transparent material, to the structure of a missile. This connecting arrangement comprises a retaining ring extending over the rim of the dome, positively holding the dome and connected to the structure of the missile. The connection is effected without material interconnection between dome and retaining ring. A groove is provided along the rim of the dome under the retaining ring. A flexible sealing means is provided in this groove for sealing between the retaining ring and the dome.
SUMMARY OF THE INVENTION
One object of the present invention is to improve a window of the above mentioned type, such that its resistance to the loads occurring during the flying phase of the missile is improved.
According to the invention this object is achieved in that the window has several window layers which support each other and which are commonly supported, wherein the material choice, the thickness and the arrangement of the window reduce mechanical stresses due to temperature during supersonic or hypersonic flight as compared to a continuously homogeneous window.
The invention is based on the following considerations: The window has to have a certain thickness in order to resist the considerable mechanical loads. A temperature gradient appears across this total thickness of the window. The window will be very hot at the outer surface and in the outer layers. The layers of the window located further inward are, at first, less heated up. In a homogenous window this would lead to thermally induced mechanical loads: The thermal dilatation is larger in the outer layers than in the inner layers. The stresses due to this fact can be reduced by using a multilayer window.
The arrangement can be such that the layers of the window are fixedly interconnected with their surfaces e.g. by being “optically interconnected” such that an “optical contact” is achieved. The expressions “optically interconnected” and “optical contact” means that the two surfaces are plain to such an extent, that, when brought into contact with each other, they adhere to each other due to intermolecular forces acting between the two surfaces. This ensures a good heat transmission between the layers and the temperature gradient is kept as small as possible. In order to prevent stresses between the layers due to the unavoidable temperature gradient, then, with respect to their coefficients of dilatation, the materials of the layers have to be chosen such that the dilatations of the layers having different temperatures are as similar as possible. The hot layers near the outer surface have to have a lower coefficient of dilatation than the colder inner layers.
However, the arrangement can also consist of providing a slip or lubricant layer between the window layers, which slip or lubricant layer allows a relative motion of the window layers parallel to their surfaces facing each other, such that the transmission of stresses between the window layers is reduced.
The durability of a window according to the invention can be 10 seconds and more. Typical times of mission of a supersonic or hypersonic target-tracking missile are in the range of 3-8 seconds. Thus, it is not necessary to provide particular protective coverings which protect the window during certain flight phases.
Further objects and features of the invention will be apparent to a person skilled in the art from the following specification of a preferred embodiment when read in conjunction with the appended claims.
REFERENCES:
patent: 4613540 (1986-09-01), Traut et al.
patent: 5182155 (1993-01-01), Roe
patent: 5457471 (1995-10-01), Epperson, Jr.
patent: 5707723 (1998-01-01), Harrison et al.
patent: 5849234 (1998-12-01), Harrison et al.
Bosch Siegfried
Fisch Peter Gerd
Bodenseewerk Geratetechnik GmbH
Gregory Bernarr E.
Mallinckrodt Robert R.
Mallinckrodt & Mallinckrodt
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