Collapsible self-erecting tubular frame structure and deployable electromagnetic reflector embodying same

Abstract

A collapsible self-erecting three-dimensional frame structure constructed of relatively thin-walled resiliently flexible tubular frame members joined at their ends in a selected geometric configuration, such as a tetrahedral truss configuration, whereby the structure is collapsible, by flattening and folding the frame members, to a compact storage configuration wherein the frame members store elastic strain energy for effecting self-erection of the structure when the collapsing forces are removed. A deployable antenna reflector embodying the frame structure.

Parent Case Text

This is a continuation of application Ser. No. 131,218 filed Apr. 5, 1971 now abandoned.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to structures of the kind which are collapsible to reduced overall size for storage. More particularly, the invention relates to a three-dimensional collapsible frame structure of the class described which is self-erecting under the force of elastic strain energy stored within the collapsed structure. The invention relates also to a deployable antenna reflector embodying the frame structure.

2. Prior Art

There is a continuing need for large truss structures and the like which can be collapsed for stowage in greatly reduced volume and subsequently deployed to envelop a volume or form planar, curved or contoured surfaces for space or terrestrial uses. Large parabolic antennas which can be contracted to a small volume for stowage in a space vehicle for launch into space orbit and then deployed are one such example. Maximum surface accuracy and minimum distortion due to mechanical loads and thermal gradients are fundamental requirements. The ultimate in design simplicity is also desired to insure deployment reliability.

Many expandable structure concepts have been proposed to fulfill these needs. Inherent disadvantages, such as inability to maintain desired accuracy in operation, unreliable deployment, design and manufacture complexities, etc., have deterred acceptance. One such concept proposed for space use, for example, is a truss reflector which exhibits good structural integrity and stability against thermal distortion, but possesses extreme mechanical complexity and hence low deployment reliability and high relative specific weight and cost.

SUMMARY OF THE INVENTION

The self-erecting collapsible structure of the present invention is constructed of a plurality of relatively slender tubular beams or frame members joined at their ends to form a unitary frame structure which normally assumes a selected geometric configuration. These frame members are hollow, relatively thin-walled, resiliently flexible sleeves or tubes which are similar to those shown in Patent Nos. 3,217,328 and 3,434,254, and may be flattened and folded to permit collapsing of the frame structure to a compact storage configuration. When thus flattened and folded, the tubular frame members store elastic strain energy which causes the members to spring back to their original shape and thereby erect the frame structure to its normal geometric configuration upon removal of the collapsing forces from the structure.

The present frame structure may assume almost an infinite variety of geometric configurations. The particular frame structure disclosed is a tetrahedral truss structure for use as a deployable antenna reflector for a spacecraft or the like. In this application, one face of the truss structure has a generally parabolic curvature and carries an electromagnetic reflective mesh which is foldable with the truss structure for storage.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of a tetrahedral truss structure according to the invention;

FIG. 2 is an enlarged fragmentary perspective view of one frame member of the truss structure;

FIG. 3 is a section through the frame member illustrating the manner in which it may be flattened for folding;

FIG. 4 is an enlarged fragmentary plan view of one joint of the truss structure;

FIG. 5 is an edge view of the joint looking in the direction of the arrow 5 in FIG. 4;

FIG. 6 is a perspective view on reduced scale of the truss structure in its collapsed configuration; and

FIG. 7 diagrammatically illustrates a preferred folding pattern of the truss structure for collapsing it to its folded configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The collapsible self-erecting frame structure 10 selected for illustration in the drawings is a tetrahedral truss structure for use as the supporting frame of a deployable spacecraft antenna reflector. This frame or truss structure is constructed of a plurality of relatively thin-walled resiliently flexible tubular beams or frame members 12 similar to those disclosed in the earlier mentioned patents. Frame members 12 are joined at their ends by connecting means 14 in a manner such that the structure normally assumes its expanded configuration of FIG. 1. The structure is collapsible to its conpact stowage configuration of FIG. 6 by flattening and folding the frame members as described presently.

The illustrated frame or truss structure has a tetrahedral truss frame with opposing sides 16, 18 which, in this instance, are generally hexagonal in edge outline and are hereafter referred to as front and rear sides, respectively. The front frame side 16 has a generally hexagonal perimeter P.sub.F comprising a number of the frame members 12 joined end to end by connecting means 14. Extending between and attached at their ends to opposing connecting means at opposite sides of the perimeter and in oblique intersecting relation to one another are a number of truss members T.sub.F comprising frame members 12 joined end to end by connecting means 14 which also join the intersecting truss members to one another at their intersections.

The rear truss frame side 18 is similar to the front frame side and has a generally hexagonal perimeter P.sub.R and intersecting truss members T.sub.R comprising frame members 12 joined end to end by connecting means 14. Truss members T.sub.R are attached at their ends to the perimeter connecting means and are attached to one another at their intersections by their connecting means.

Extending between and attached at their ends to the connecting means 14 of the front and rear frame sides 16, 18 are frame members 12 providing normal and diagonal connecting struts S which join the frame sides into a unitary frame structure. As may be readily observed in the drawings, the several frame members of the truss structure 10 form a number of tetrahedral frame portions, that is portions of the overall frame consisting of six frame members 12 arranged in a tetrahedral configuration. These tetrahedral frame portions are hereafter referred to as tetrahedral bays and have triangular faces in the front and rear frame sides 16, 18.

The frame members 12 of the truss structure 10 are constructed of a resiliently flexible material, such as a heat treated plastic-like Mylar or Kapton, or metal, which is formed to the flanged tubular beam configuration illustrated in FIGS. 2 and 3. In this case, the frame members are formed in two mating flanged sections whose flanges are joined by stitching 19 to provide frame members or beams of the kind disclosed in copending application Ser. No. 130,574, filed Apr. 2, 1971, under TRW Docket No. 4891, and entitled "Strain Energy Erectile Tubular Beam with Stitched Flanges". This resilient construction of the frame members permits them to be flattened, as shown in broken lines in FIG. 3, and then folded in such a way as to enable collapsing of the truss structure to its storage configuration of FIG. 6.

A significant feature of the illustrated truss structure resides in the fact that each intersection connecting means 14 must accommodate a number of the frame members 12 which must hinge immediately adjacent the intersections. Some of the intersections, for example, such as that shown in FIGS. 4 and 5, must accommodate six substantially coplanar frame members and three diagonal frame members or struts S. This is accomplished by using connecting means in the form of hexagonal plate-like fittings 28 and flattening the ends of the frame members and securing their flattened ends to the fittings with rivets 30 or the like. The diagonal struts of each intersection are attached to the underside of its connecting fitting. The flat pinched ends of the frame members permits the latter to hinge freely on hinge axes adjacent and substantially coplanar with their respective connecting fittings. This is a significant feature of the design, since the frame members possess maximum bending strength about axes normal to the planes of the connecting fittings when either flattened or fully open. Hence, the truss connecting fittings are stabilized in their normal orientation when the structure is either folded or deployed.

The fold pattern for the illustrated truss structure is diagrammatically illustrated in FIG. 7 and involves folding or doubling the frame members 12 of the front and rear perimeters P.sub.F, P.sub.R, and truss members T.sub.F, F.sub.R at their centers in inverted "V" fashion. The diagonal truss members or struts S are not folded, but swing laterally inward in a manner similar to closing a camera tripod. This fold pattern provides the folded truss structure (FIG. 6) with an overall diameter approximating the cumulative "across flat" dimensions of the individual hexagonal intersection fittings. In order to further reduce packaged size, the frame members in the upper and lower surfaces may be tapered toward their ends. This reduces the intersection fittings size and also results in a truss member configuration which receives column load more efficiently, being larger in diameter at its midpoint.

As noted earlier, the illustrated truss structure is the supporting frame of a deployable electromagnetic reflector for a spacecraft antenna or the like. The RF reflective surface of the antenna is provided by a foldable wire mesh 32 (shown in fragmentary fashion) fixed to the front side 16 of the truss structure. This front side of the structure is provided with the desired contour, in this instance a parabolic contour, by dimensioning the connecting struts S of the truss structure in such a way that the frame members 12 located in the plane of the front side conform generally to, i.e. are tangent to, a theoretical parabolic surface. Improved conformance of the front truss side to a parabolic surface may be accomplished in curving the frame members of the front truss frame side 16. When the reflector is folded to its storage configuration, the mesh 32 nests between the folded front frame members, as shown in FIG. 7, and does not interfer with folding or deployment of the reflector.

An advantage of the illustrated antenna resides in the fact that its open construction achieves uniform exposure of virtually all parts of the structure to incident solar flux regardless of the orientation of the antenna relative to the sun.

It will now be understood that the illustrated reflector is collapsible to its compact stowage configuration of FIG. 6 by flattening and folding of the frame members 12. When thus folded, the frame members store elastic strain energy which causes self-erection or deployment of the reflector to its expanded or deployed configuration of FIG. 1 when released.

Claims

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

1. A deployable antenna reflector for spacecraft and the like comprising:

a tetrahedral truss frame constructed of thin-walled, resilient, collapsible, strain energy erectile tubular frame members and having two spaced and generally parallel frame sections forming opposite sides of said frame and connecting struts between and joining said frame sections;

each frame section having a perimeter comprising a number of said tubular frame members joined end to end by first connecting means, and truss members each comprising a number of said tubular frame members joined end to end by second connecting means, said truss members extending between opposite sides of said perimeter in oblique intersecting relation to one another and being joined at their ends to said perimeter by said first connecting means and between their ends to one another at the truss member intersections by said second connecting means, and connecting struts comprising tubular frame members extending between and joined at their ends by said connecting means to said frame sections in such a way as to form with the tubular frame members of said frame sections a plurality of tetrahedral bays;

each said tubular frame member having a tubular portion and coplanar dimetrically opposed flanges along opposite sides of said tubular portion and the ends of the tubular portion of each frame member being flattened into coplanar relation with its flanges;

each said connecting means comprising a flat connecting plate located substantially in the plane of the corresponding frame section and seating the adjacent flattened frame member ends, each plate having an edge underlying the flattened end of and extending transverse to each of the corresponding frame members, and means joining the member ends to their respective connecting plates;

the outer side of one frame section conforming generally to an arcuate surface of selected contour, such as a parabolic surface;

a flexible and foldable electrically conductive mesh secured to said outer side of said one frame section in a manner such that said mesh conforms generally to said surface contour to provide an electromagnetic reflecting surface when said truss frame occupies said tetrahedral truss configuration; and

said frame members being adapted to be flattened and folded and said mesh being adapted to be folded with said frame members to permit collapsing of said reflector to a compact storage configuration wherein said frame members store elastic strain energy for deploying said reflector when the collapsing force on the reflector is removed.