GB2120857A

GB2120857A - Reflectors

Info

Publication number: GB2120857A
Application number: GB08311437A
Authority: GB
Inventors: Dr James Francis Clemmet
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1982-04-28
Filing date: 1983-04-27
Publication date: 1983-12-07
Also published as: GB8311437D0; GB2120857B

Abstract

A reflector arrangement comprises first and second flexible surface elements 14 in parallel spaced relationship and each in a state of tension. A flexible active surface element 16 is located between the first and second flexible surface elements 14 in a predetermined configuration by means of tension members 15 extending between opposed points on the first and second surface elements 14 respectively. The first and second surface elements may be supported by telescopically extendable frame members so that the whole arrangement may be stowed in a small volume. <IMAGE>

Description

SPECIFICATION Reflectors This invention relates to reflector arrangements and in particular, but not exclusively, to reflectors for use in antenna arrangements deployable from a stowed compact condition to an extended, deployable condition for use, for example, on a spacecraft.

With the increasing pressures for more precise control of antenna beam shape and cross polar levels in commercial satellites, there will inevitably be a growing need for systems which use largediameter reflectors on board the spacecraft; this demand is further increased by the greater power capability of forthcoming communications satellites.

Attempts to provide a reflector arrangement which satisfies these criteria have had various disadvantages associated with them, namely the stowed configuration on the spacecraft, poor packaging efficiency, crude systematic shaping of the working surface, unsuitability for offset feed geometry, uncontrolled deployment and the need for complex ground procedures to account for gravitational effects. It is an aim of this invention to overcome or reduce at least some of these disadvantages.

According to one aspect of this invention, there is provided a reflector arrangement which comprises first and second flexible surface elements, a plurality of tension members and a flexible reflector active surface element, said first and second surfaces being maintained in a state of tension and being arranged on opposed sides of the flexible reflector surface element, the flexible reflector surface being maintained in a predetermined configuration by means of the tension members which extend between associated surface portions of the reflector surface and the first and second surface elements. The tension members preferably extend between associated portions of the first and second surface elements and carry, intermediate their ends, a portion of the reflector surface.

Naturally, the surface element through which radiation passes to and from the reflector active surface should be substantially transparent to the radiation of interest, as should the tension members.

According to a second aspect of th is invention, there is provided a reflector arrangement deployable from a stowed compact condition to an extended deployed condition, said arrangement comprising first and second flexible surface elements and a plurality of tension members, first and second extendable frame means associated with said first and second surface elements each movable from a stowed compact condition to an extended condition in which the associated surface element is in a state of tension, said tension members spanning said first and second surface elements and adapted, when both of said frame means are extended, to be in a state of tension, and a flexible reflector active surface secured to at least some of said tension members at pre-selected positions such that when said first and second frame means are extended, the reflector active surface is maintained in a predetermined configuration.

In either aspect, the reflector active surface may comprise a mesh or continuous membrane which may or may not be frequency selective.

The first and second flexible surface elements may be substantially planar and parallel; alternatively, they may converge to a common axis.

The first and second flexible surface elements may be formed of aramid fibre such as that marketed under the Trade Mark "Kevlar" by du Pont, or of quartz fibre.

The first and second flexible surface elements may be in the form of a mesh, or they may be in the form of a substantially continuous surface.

By way of example only, certain specific embodiments of reflector arrangement will now be described in detail, reference being made to the accompanying drawings in which: Figure 1 is a general perspective view of an embodiment of reflector arrangement in an extended condition; Figure2 is a side view of the embodiment illustrated in Figure 1; Figure 3 illustrates a typical configuration of the embodiment of Figure 1 when installed on a spacecraft, both in a stowed condition and an extended condition; Figure 4 illustrates three embodiments of antenna arrangement employing an embodiment of reflector arrangement, as illustrated in Figure 1, in conjunction with a centrally positioned feed horn, and Figure 5 illustrates a further embodiment of reflector arrangement.

Referring initially to Figures 1 to 4, the embodiment of reflector arrangement 10 comprises twin spaced upper and lower rectangular open frame members 11 and 12 spaced apart in parallel by means of four struts 13 extending between associated corners of the frame. A flexible mesh surface element 14 is attached to each frame member by means of ties spaced around its periphery. In the extended condition, each surface element is under a degree of tension and the surfaces are spanned at a plurality of points by means of control ties 15 which also are under tension. The control ties 15 and upper and lower surface elements are formed of a material transparent to the range of operating frequencies of the reflector.

A flexible active surface element 16, for example a mesh of conducting material, is located between the upper and lower surface elements 14 and is attached to the control ties 15 at respective locations along their length such that when the arrangement is in an extended position, the active surface adopts a preselected operating profile. In this manner, certain selected points on the reflector surfaces are plotted in terms of the position of the control tie on the upper/lower surface and the distance between the attachment to the reflector surface and the upper/ lower surface.

Each open frame member comprises four telesco picallyextendableside members 17, 17', 18, 18', which allow the reflector arrangement to be extended from a stowed compact condition to the condition illustrated in Figure 1. Side members 17 and 17' are double-acting, that is to say they comprise a housing tube 19, 19' from each end of which extend a series of tubes, whilst side members 14, 14' are single-acting, that is to say comprise a housing tube 20 from one end of which extend a series of tubes.

The side members may be driven by means of pressurized gas from a stowed to an extended configuration, for example as described in our published Application No. GB 2,062,960A, or by means of a flexible drive, for example as described in our published Application No. GB. 2,074,981A. As yet a further alternative, spiral extendable members may be employed.

The extended reflector arrangement is further braced against movement by means of shear structural ties 22.

Referring now to Figure 3, there is illustrated the just described embodiment of reflector arrangement installed on a spacecraft sidewall. Figures 3a and b show the stowed arrangement in side view and in front view respectively. The reflector arrangement is attached to the spacecraft side wall by means of housing tubes 19, and both open frame members 11 and 12 are retracted to define a relatively densely packed configuration within the confines of which the active surface member and the upper and lower surface member are contained. To reduce yet further the obstruction caused by the reflector arrangement when stowed, it may be rotated aboutthe axes of housing tubes 19 to adopt the position shown in Figure 3a.

On operation of the actuation means (not shown), the structure is rotated about housing tubes 17 and then the upper and lower open frame members are extended thereby tensioning upper and lower surface members and the control ties and causing the active surface member to adopt its pre-determined profile. The example illustrated employs an offset feed 20 and the profile of the active surface member will be selected accordingly.

Figure 4 illustrates various arrangements for mounting a centre feed for use with the embodiment of reflector arrangement illustrated in Figure 1; the feed 20 may be cantilevered from a side of the open frame structure (Figure 4a); it may be supported by means of four arms pivotally attached to the corners of the open frame structure (Figure 4b); or it may be supported by a central tubular support which is anchored to a fixed surface and which also supports the reflector arrangement (Figure 4c).

Referring to Figure 5, where the profile of the extended active surface element 16 allows, the side cross section of the reflector arrangement may be triangular rather than rectangular, the upper and lower surface elements 14 converging at one end to be secured to a single side member 19.

By the above arrangements, the active surface may be precisely shaped to operate with offset or central feed configurations and the control ties may be randomiy located to avoid the problems associated with systematic shaping.

The open frame support does not engross into antenna beam aperture and may be of other shapes than rectangular, for example, circular or elliptical.

The extension of the frame may be velocity controlled and synchronized.

Claims

1. A reflector arrangement which comprises first and second flexible surface elements and a plurality of tension members, and a flexible reflector active surface element, said first and second surfaces being maintained in a state of tension and being arranged on opposed sides of the flexible reflector active surface element, the flexible reflector surface being maintained in a predetermined configuration by means of the tension members which extend between associated surface portions of the reflector surface and the first and second surface elements.

2. A reflector arrangement deployable from a stowed compact condition to an extended, deployed condition, said arrangement comprising first and second flexible surface elements and a plurality of tension members, first and second extendable frame means associated with said first and second surface elements, each movable from a stowed compact condition to an extended condition in which the associated surface element is in a state of tension, said tension members spanning said first and second surface elements and adapted, when both of said frame means are extended, to be in a state of tension, and a flexible reflector active surface secured to at least some of said tension members at pre-selected positions such that when said first and second frame means are extended, the reflector active surface is maintained in a predetermined configuration.

3. A reflector arrangement as claimed in Claim 1 or Claim 2, wherein said first and second flexible surface elements are substantially planar and in parallel opposed relationship.

4. A reflector arrangement as claimed in Claim 1 or Claim 2, wherein said first and second flexible surface elements are substantially planar and converge to a common axis.

5. A reflector arrangement as claimed in any of the preceding Claims, wherein the reflector active surface is in the form of a mesh.

6. A reflector arrangement as claimed in any of the preceding Claims, wherein said first and second flexible surface elements are each in the form of a mesh.

7. A reflector arrangement according to Claim 2, wherein each frame is of generally rectangular form defined by opposed pairs of telescopically extendable side members.

8. A reflector arrangement substantially as hereinbefore described, with reference to and as illustrated in any of the accompanying drawings.