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Publication numberUS3694059 A
Publication typeGrant
Publication dateSep 26, 1972
Filing dateSep 30, 1970
Priority dateSep 30, 1970
Publication numberUS 3694059 A, US 3694059A, US-A-3694059, US3694059 A, US3694059A
InventorsWilliam B J Shakespeare
Original AssigneeTrw Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Lightweight composite reflector dish
US 3694059 A
Abstract
A lightweight precision dish structure for reflectors, particularly large parabolic microwave reflectors for space applications. The dish structure has a laminated reflector dish with a central core and bonded facing sheets of differing coefficients of thermal expansion, and a rigid reinforcing ring secured by adjustable fastening means to the rear convex side of the reflector dish and having a coefficient of thermal expansion closely approximating the resultant coefficient of the dish. The reinforcing ring and its adjustable fastening means permit initial adjustment of the dish to a precise parabolic or other configuration and prevent later thermal distortion of the dish as a consequence of the differing coefficients of its core and facing sheets in an adverse, asymmetric thermal environment.
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Description  (OCR text may contain errors)

United States Patent Shakespeare [451 Sept. 26, 1972 4] LIGHTWEIGHT COMPOSITE REFLECTOR DISH [73] Assignee: TRW Inc., Redondo Beach, Calif.

[22] Filed: Sept. 30, 1970 [21] Appl. No.: 76,741

[52] US. Cl. ..350/310, 161/68, 343/912 [51] Int. Cl. ..COZb 7/18 [58] Field of Search ..343/840, 912; 350/310, 288,

[56] References Cited UNITED STATES PATENTS 2,742,387 4/1956 Giuliani ..343/912 3,326,624 6/1967 Maydell et a1. ..350/288 X 2,798,478 7/1957 Tarcici ..350/296 X 3,150,030 9/1964 Mondano ..161/68 3,001,196 9/1961 Mcllroy et al. ..343/915 Primary ExaminerDavid Schonberg Assistant Examiner-John W. Leonard Attorney-Daniel T. Anderson, Donald R. Nyhagen and Jerry A. Dinardo 5 7] ABSTRACT A lightweight precision dish structure for reflectors, particularly large parabolic microwave reflectors for space applications. The dish structure has a laminated reflector dish with a central core and bonded facing sheets of differing coefiicients of thermal expansion, and a rigid reinforcing ring secured by adjustable fastening means to the rear convex side of the reflector dish and having a coefficient of thermal expansion closely approximating the resultant coefficient of the dish. The reinforcing ring and its adjustable fastening means permit initial adjustment of the dish to a precise parabolic or other configuration and prevent later thermal distortion of the dish as a consequence of the differing coefficients of its core and facing sheets in an adverse, asymmetric thermal environment.

2 Claims, 2 Drawing Figures PATENTEUSEPZS I972 William BJ. Shakespeare I N V EN TOR.

ATTORNEY LIGHTWEIGHT COMPOSITE REFLECTOR DISH The invention herein described was made in the course of or -under a contract or subcontract thereunder, (or grant) with the Department of the Air Force.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to reflectors, especially large parabolic microwave reflectors for space applications. More particularly, the invention relates to a lightweight precision dish structure for such reflectors.

2. Prior Art As will become evident from the ensuing description, the invention may be utilized in a variety of reflectors for both terrestrial and space applications. However, the principal application of the invention is a large parabolic microwave reflector for space use. The invention will be disclosed in connection with such use.

A reflector intended for space applications is subject to conflicting design constraints which heretofore have been difficult, if not impossible, to satisfy. Thus, in order to minimize structural deformation of the reflector due to temperature cycles in space, such as are experienced in certain orbital flights, the reflector must be constructed of materials having low coefficients of thermal expansion. However, even when constructed of such materials, the reflector is subject to significant thermal expansion and contraction when exposed to extreme temperature cycles and must possess sufficient stiffness to maintain its close tolerance profile under such temperature cycling. On the other hand, normal launch dynamic conditions impose on the reflector the constraint -of lightweight construction which is inherently characterized by relatively low finite stiffness.

At the present state of the art, the above design constraints can best be satisfied by utilizing a laminated reflector dish consisting of a central core of aluminum honeycomb or other similar material and resin impregnated facing sheets bonded to the front concave and rear convex sides of the core. However, the resulting reflector is a non-homogeneous structure which displays inherent unpredictable creep characteristics. Because of these creep characteristics, the reflector dish, when exposed to extreme temperature cycles, tends to deform, primarily within a concentric annular band or region adjacent the rim of the dish in a manner which produces within such region wavelike distortions. These distortions are unacceptable within the constraints of the close tolerances limits of the reflector profile.

SUMMARY OF THE INVENTION The present invention avoids the distortion problems and satisfies the design constraints discussed above and thus provides a lightweight precision reflector dish structure which is ideally suited for space applications involving extreme temperature cycles. According to the invention, the laminated reflector dish is stiffened or reinforced by a relatively rigid ring concentrically surrounding the rear side of the dish adjacent its rim. This ring is attached to the reflector dish at positions spaced uniformly about the ring by adjustable fastening means. In the disclosed inventive embodiment, these fastening means comprise screws which pass through the ring and are threaded in the reflector dish and shims which may be placed between the ring and dish. The ring is constructed of a material which has a coefficient of thermal expansion closely approximating the overall or resultant coefficient of thermal expansion of the laminated reflector dish.

During initial assembly of the dish structure, the reflector dish is adjusted to the desired profile or shape by the adjustable ring-dish fastening means. In the disclosed embodiment, for example, this adjustment involves adjustment of the ring screws and selective placement of shims between the ring and dish in such a way as to draw the dish to the desired profile. Subsequently, in operational use of the reflector, the ring serves to reinforce or stiffen the reflector dish against distortion when exposed to extreme temperature cycles and thereby preserves the close tolerance profile of the dish.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a rear view of a parabolic reflector dish structure according to the invention; and

FIG. 2 is an enlarged section taken on line 2-2 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings illustrate a lightweight precision reflector dish structure 10 according to the invention. This dish structure includes a reflector dish 12 proper, a reinforcing or stiffening ring 14 concentrically surrounding the rear convex side of the dish adjacent its rim, and adjustable fastening means 16 joining the ring and dish at positions spaced uniformly about the ring. In this instance, the reflector dish 12 is a parabolic dish whose front concave surface is coated with a metallic film to form a parabolic microwave reflector for installation on an orbiting space satellite.

The reflector dish 12 has a laminated construction and includes a central core 18 and facing sheets 20, 22 bonded and conforming to the front and rear faces of the core. For the space application referred to above, the core comprises a high strength lightweight material having a low coefficient of thermal expansion, such as aluminum honeycomb. The facing sheets comprise high strength resin impregnated Fiberglas bonded to the core.

Dish 12 is fabricated by applying the facing sheets to the honeycomb core to form a laminated structure and then forming this laminated structure into a dish between a pair of forming dies having the desired profile of the finished dish. After forming, the dish is cured to relieve the stresses produced during the forming operation. As noted earlier, a laminated dish of this kind is a non-homogenous structure which possesses unpredictable creep characteristics. It has been found that owing to these creep characteristics, the dish tends to creep and deform when exposed to the temperature changes or cycles which occur during the stress relieving process and later during operational use of the reflector in space, particularly in some orbital flights which produce extreme temperature changes or cycles. However, this deformation of the dish occurs only within the annular region R of the dish extending radially in from its rim, a distance approximating one-third the radius of the dish. The remaining central region of the dish remains undeformed and conforms to the desired dish profile.

Deformation of the dish 12 within the region R takes the form of wavelike distortions. These distortions are unacceptable within the close tolerance limits of a dish for a parabolic reflector.

The stiffening ring 14 constitutes a major improvement feature of the invention. The ring and its fastening means 16 serve two purposes, namely initial adjustment of the reflector dish to its proper profile or contour,

and retention of this profile during operational use of the reflector. To this end, the ring surrounds the rear side of the reflector dish 12 within the region R of dish distortion. The ring is constructed of a material whose coefficient of thermal expansion closely approximates the overall or resultant coefficient of thermal expansion of the laminated dish. For a composite dish having an aluminum honeycomb core and resin impregnated facing sheets for example, the stiffening ring may comprise a stainless steel tube. The ring fastening means comprise screws 24 which pass through holes in the wall of the ring adjacent the dish and are threaded in inserts 26 bonded within the dish. The fastening means also include shims 28 which are adapted to be placed on selected screws between the dish and the ring. Screws 24 are arranged at uniform intervals about the dish.

Stiffening ring 14 is diametrically sized to closely ap proximate diameter of the reflector dish at the plane of attachment of the ring to the dish, such that this dish region may be forced or adjusted to the proper profile by tightening the ring attachment screws 24 to firmly clamp the dish to the ring. Shims 28 are placed between the dish and the ring as required to provide the dish with the proper profile. During subsequent operational use of the reflector, when the latter is subjected to extreme temperature cycles, the dish 12 and ring 14 expand and contract in unison so that the ring retains the outer region R of the dish in the proper profile.

The number of ring fastening screws 24 depends on the diameter of the dish. For a 44-inch diameter dish, for example, 32 fastening means have been found to be suitable. While the illustrated dish has only a single stiffening ring 14, it will be understood that additional rings may be employed, if necessary. One ring has been found to be sufficient for a 44-inch parabolic dish, for example. Larger reflector dishes may require additional rings.

What is claimed as new in support of Letters Patent is:

1. A lightweight precision reflector dish structure comprising a laminated reflector dish including a central core having a front concave face and a rear convex face, and facing sheets conforming and bonded to said core faces:

said core and facing sheets having differing coefficients of thermal expansion such that said dish tends to creep in a thermal environment, thereby creating wavelike distortions within a concentric annular region of said dish adjacent its rim;

a relatively rigid reinforcing ring of smaller diameter than the rim diameter of said dish concentrically surrounding the rear side of said dish within said annular region; ad ustable fastening means oining said ring and dish at a number of positions uniformly spaced about said ring;

said fastening means being adjustable to remove said distortions and conform the front facing sheet to a selected surface of revolution; and

said ring having a coefficient of thermal expansion closely approximating the resultant coefficient of thermal expansion of said dish.

2. A reflector dish structure according to claim 1 wherein:

said fastening means comprise screws passing through said ring and threaded in said dish and adapted to receive shims between said ring and dish.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2742387 *Sep 28, 1953Apr 17, 1956Lavoie Lab IncReflector for electromagnetic radiations and method of making same
US2798478 *Oct 28, 1952Jul 9, 1957Tarcici AdnanFlexible reflectors
US3001196 *Jan 16, 1959Sep 19, 1961Gen Dynamics CorpDual pattern antenna
US3150030 *Apr 6, 1960Sep 22, 1964Raytheon CoLaminated plastic structure
US3326624 *Jun 13, 1963Jun 20, 1967Bolkow GmbhInflatable mirror construction capable of being formed into a permanently rigid structure
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4484198 *Mar 29, 1982Nov 20, 1984Thomson-CsfAntenna support system with two dimension flexibility
US4500170 *Jun 14, 1982Feb 19, 1985Ford Aerospace & Communications CorporationGravity and temperature compensating reflector support actuator
US4673950 *Jul 17, 1985Jun 16, 1987Piper Robert JAntenna and method for fabricating same
US4791432 *Dec 24, 1986Dec 13, 1988Piper Robert JAntenna and method for fabricating same
US5202689 *Aug 23, 1991Apr 13, 1993Apti, Inc.Lightweight focusing reflector for space
US6064352 *Apr 1, 1998May 16, 2000Trw Inc.Composite isogrid structures for parabolic surfaces
US20130114155 *Dec 21, 2012May 9, 2013Konica Minolta Layers, Inc.Reflective panel for solar power generation
DE3606547A1 *Feb 28, 1986Sep 3, 1987Messerschmitt Boelkow BlohmMirror tracking system for coelostats
EP0000913A1 *Aug 14, 1978Mar 7, 1979M.A.N. MASCHINENFABRIK AUGSBURG-NÜRNBERG AktiengesellschaftReflector for solar collectors
Classifications
U.S. Classification359/848, 428/119, 428/152, 428/64.1, 343/912, 359/883, 428/115
International ClassificationF24J2/12, G02B7/18, G02B5/08
Cooperative ClassificationG02B7/181, Y02E10/42, F24J2/12, G02B5/08
European ClassificationG02B7/18T, G02B5/08, F24J2/12