US20090133355A1

US20090133355A1 - Deployable Membrane Structure

Info

Publication number: US20090133355A1
Application number: US11/945,898
Authority: US
Inventors: Mehran Mobrem
Original assignee: Northrop Grumman Space and Mission Systems Corp
Current assignee: Northrop Grumman Systems Corp
Priority date: 2007-11-27
Filing date: 2007-11-27
Publication date: 2009-05-28

Abstract

A deployable structure (10) includes at least two membranes (20) arranged overlying each other and spaced apart from each other. A deployable perimeter truss structure (40) encircles the at least two membranes (20). A transition truss structure (80) connects the membranes (20) to the perimeter truss structure (40). The perimeter truss structure (40), transition truss structure (80), and membranes (20) form a pre-loaded truss structure in which the membranes comprise integral tension transmitting components of the tensioned truss structure.

Description

TECHNICAL FIELD

The present invention relates to a deployable structure and, more particularly, to a structure for terrestrial and space-based deployment of a membrane, such as a sunshield.

BACKGROUND

Deployable structures are used to deploy membranes, such as sunshields or RF reflectors in terrestrial and space based (e.g., satellite) applications. Typical deployable structures include a foldable framework that supports a reflective surface, such as a foldable membrane. In one such application, a deployable reflector in the form of a sunscreen is deployed to help reflect or otherwise block harmful radiation, such as ultraviolet (UV) radiation from the sun, from interfering with instrumentation or other satellite mounted devices.

SUMMARY OF THE INVENTION

The present invention relates to a deployable structure that includes at least two membranes arranged overlying each other and spaced apart from each other. A deployable perimeter truss structure encircles the at least two membranes. A transition truss structure connects the membranes to the perimeter truss structure. The perimeter truss structure, transition truss structure, and membranes form a tensioned truss structure in which the membranes comprise integral tension transmitting components of the tensioned truss structure.
In another aspect of the invention, the deployable structure also includes a catenary associated with each of the at least two membranes. Each catenary encircles its associated membrane and is connected to its associated membrane at interfaces spaced about a periphery of the associated membrane.
In an aspect of the invention, the deployable structure also includes tension springs that interconnect adjacent and overlying ones of the interfaces on the at least two membranes.
In another aspect of the invention, the transition truss structure is connected to the interfaces to thereby connect the membranes to the perimeter truss structure.
In another aspect of the invention, each catenary is connected to the interfaces for sliding movement relative to the associated membrane.
In another aspect of the invention, each catenary is fixed to the interfaces.
In another aspect of the invention, the transition truss structure includes at least one cable interconnecting the interfaces on each membrane to the perimeter truss structure.
In another aspect of the invention, the at least two membranes comprise sunshields.
In another aspect of the invention, the springs exert a spring force that urges the interfaces toward each other and tensions the catenaries, which applies a tension across the membranes and through the transition truss to the perimeter truss.
In another aspect of the invention, the catenaries help distribute the tension evenly across the membranes.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following description of the invention with reference to the accompanying drawings.

FIG. 1 illustrates a schematic perspective view of a deployable structure in an example implementation according to the invention.

FIG. 2 illustrates a schematic perspective view of the deployable structure illustrated in FIG. 1.

FIG. 3 illustrates an exploded perspective view of the deployable structure illustrated in FIG. 1.

FIG. 4 illustrates a schematic perspective view of the deployable structure illustrated in FIG. 1 taken from a different perspective.

FIG. 5 illustrates a magnified schematic perspective view of a portion of the deployable structure illustrated in FIG. 5.

FIG. 6 illustrates a schematic elevation view of a deployable structure in accordance with an alternative embodiment of the invention.

DETAILED DESCRIPTION

The present invention relates to a deployable structure for terrestrial and space-based (e.g., satellite) deployment. In the embodiments shown and described herein, the deployable structure deploys membranes that serve as sunshields. Those skilled in the art, however, will appreciate that the deployable structure could be used to deploy membranes that serve an alternative function, such as that of a reflector, antenna, or solar array. By way of example, as shown in FIG. 1, a deployable structure 10 is supported on a satellite 12 by a deployment arm 14. In this example implementation, membranes 20 form a sunshield 22 that help prevent portions of the satellite 12 from being exposed to radiation, e.g., solar radiation.
Referring to FIGS. 2-5, the sunshield 22 comprises multiple (i.e., two or more) membranes 20 arranged concentric, overlying each other, and spaced apart along a central axis 24. In the embodiment illustrated in FIGS. 2 and 3, the membranes 20 include a first or upper membrane 26 and a second or lower membrane 28. The membranes 20 are supported by a truss structure 30 that includes a perimeter truss structure 40 and a transitional truss structure 80. The perimeter truss structure 40 is centered on the axis 24 and defines a closed periphery that encircles the membranes 20. The transitional truss structure 80 is connected to the perimeter truss structure 40 and to the membranes 20 at interfaces 82 (best illustrated in FIG. 5) spaced about the periphery 84 of the membranes. The deployable structure 10 also includes a catenary cable 100 (see FIG. 5) associated with each membrane 20, i.e., a first catenary cable 102 is associated with the first membrane 26 and a second catenary cable 104 associated with the second membrane 28. The deployable structure 10 further includes tensioning members 110, such as springs, that interconnect overlying pairs of the interfaces 82.
The perimeter truss structure 40 is a rigid truss structure that includes rigid truss members 42 that are interconnected by fittings 44 that permit the truss members to pivot relative to each other. The truss members 42 are generally lightweight, rigid, and strong, and may be constructed of any suitable material or materials that possess the desired combination of these properties. For example, the truss members 42 may be constructed of graphite fiber rods or tubes. Those skilled in the art will appreciate that alternative materials, such as carbon fiber or titanium, may be used construct the truss members 42.
The truss members 42 include longerons 50 that are arranged circumferentially about the axis in an end-to-end configuration and connected to each other by the fittings 44. The longerons 50 help define a first or upper chord 52 and a second or lower chord 54. The upper and lower chords 52 and 54 are generally circular in form, radially stiff, centered on, and extend circumferentially about the axis 24. The upper chord 52 and lower chord 54 are spaced apart from each other along the axis 24. The truss members 42 also include battens 60 that extend axially between the upper chord 52 and lower chord 54 and are connected to the fittings 44. The battens 60 are thus spaced circumferentially about the perimeter truss structure 40 and provide an axially stiff interconnection between the upper and lower chords 52 and 54.
As best shown in FIG. 5, the fittings 44 have a generally T-shaped configuration. The fittings 44 interconnect the longerons 50 and battens 60 in a generally perpendicular or T-shaped configuration when the deployable structure is in the deployed condition. The fittings 44 are constructed and arranged in a manner known in the art that permits the longerons 50 to pivot about respective axes 62 relative to the battens 60, while maintaining the axial orientation of the battens. The fittings 44 permit the longerons 50 to pivot either upward about the axis 62 relative to the associated batten 60 (indicated generally by the arrows labeled “UP” in FIG. 5) or downward about the axis 62 relative to the associated batten (indicated generally by the arrows labeled “DOWN” in FIG. 5).
The perimeter truss structure 40 also includes diagonals 70 that interconnect the fittings 44 of the upper and lower chords 52 and 54. The diagonals 70 may have various configurations or constructions. For example, the diagonals 70 may comprise rigid truss members having a configuration and construction similar to that of the longerons 50. As another example, the diagonals 70 may comprise flexible elongated members, such as strings or cables, that extend diagonally from the fittings 44 on one of the chords 52 and 54 to the fittings on the other of the chords to improve the stability of the perimeter truss structure 40. The flexible diagonals 70 may be constructed of any suitable material or materials, such as Aramid fiber (e.g., Kevlar™) strings or cables. Each fitting 44 has associated with it (one, two or none) rigid or two flexible diagonals 70, one extending to the fitting spaced one position on each side of the corresponding fitting of the opposite chord. Thus, for example, referring to FIG. 3, for the fitting identified at 44A, a first diagonal 70A1 extends diagonally up and to the left to a fitting on the upper chord 52, and a second diagonal 70A2 extends diagonally up and to the right to a fitting on the upper chord. Similarly, the for the fitting identified at 44B, a first diagonal 70B1 extends diagonally down and to the left to a fitting on the lower chord 54, and a second diagonal 70B2 extends diagonally down and to the right to a fitting on the lower chord. If rigid diagonals 70 are implemented, the perimeter truss structure 40 may include only a single diagonal per bay, in a continuous and alternating manner (i.e., diagonally up and to the right in one bay, and then diagonally down and to the right in the right adjacent bay).
The fittings 44 are configured such that the longerons 50 of the upper and lower chords 52 and 54 associated with any particular batten 60 all pivot in the same direction, i.e., upward or downward. The fittings 44 are arranged such that the longerons 50 associated with the battens 60 pivot upward/downward in an alternating fashion about the circumference of the perimeter truss structure 40. In this manner, the perimeter truss structure 40 can be moved from the deployed condition illustrated in FIGS. 1-5 in which the longerons 50 extend perpendicular to the battens 60, to a non-deployed condition (not shown) in which the longerons are pivoted to extend parallel or substantially parallel to the battens. As the perimeter truss structure 40 moves toward the non-deployed position, the truss structure is drawn inward toward the axis 24 and the overall diameter of the perimeter truss structure is reduced.
The membranes 20 may be constructed of any material suited to perform the desired functions. For example, in the sunshield implementation described above, the membranes 20 each may comprise a film that may be coated with a reflective material. One example of a film that may be used to construct the membranes 20 is Kapton™, which is a polyimide film produced by E.I. du Pont de Nemours and Company of Wilmington, Del. The chemical name for Kapton™ is poly(4,4′-oxydiphenylene-pyromellitimide). Alternative film materials, such as CP1™ and CP2™ polyimide films and Mylar™ polyester films may also be used to construct the membranes 20. In one particular configuration, the membranes 20 may comprise Aluminized (i.e., aluminum coated) Kapton™ film membranes.
Referring to FIGS. 4 and 5, the periphery 84 of each membrane 20 is cut or otherwise configured in a series of arcs 86 arranged end-to-end about the periphery. The interfaces 82 are positioned at each intersection where adjacent arcs 86 meet each other. Between the interfaces 82, guides 90 are secured to the periphery 84 at spaced locations along the arcs 86. The guides 90 and interfaces 82 may have any configuration suited to guide the catenary cables 100 and, in the case of the interfaces, connect with the tensioning members 110 and the transitional truss structure 80. For example, the guides 90 and interfaces 82 may comprise eye hooks or eyelets secured, bonded, or otherwise connected to the membranes 20 by suitable means, such as an adhesive or tape (e.g., Kapton™ tape). As another example, the guides 90 may comprise tubular members (not shown), secured to the membranes 20 (e.g., by Kapton™ tape), and through which the catenary cables 100 extend.
The catenary cables 100 extend through and are guided about the periphery 84 of the membranes 20 and along the arcs 86 by the interfaces 82 and guides 90. More particularly, the first catenary cable 102 extends through and is guided about the periphery 84 of the first membrane 26 by the interfaces 82 and guides 90 on the first membrane. Likewise, the second catenary cable 104 extends through and is guided about the periphery 84 of the second membrane 28 by the interfaces 82 and guides 90 on the second membrane.
The transitional truss structure 80 secures the membranes 20 to the perimeter truss structure 40 and may have any construction or configuration suited to do so. For example, the transitional truss structure 80 may comprise one or more flexible elongated members, such as cables, that extend orthogonally or diagonally from the fittings 44 on the perimeter truss structure 40 to the interfaces 82 on the membranes 20. The transitional truss structure 80 may be constructed of any suitable material or materials, such as Kevlar™ strings or cables. The transitional truss structure 80 may comprise a single length of cable that is looped through the interfaces 82 and through corresponding eyelets or guides on the fittings 44. Alternatively, the transitional truss structure 80 may comprise segments connected (e.g., via terminations) to the interfaces 82 individually.
The tensioning members 110 extend between and interconnect the interfaces 82. According to the present invention, the perimeter truss structure 40 and transitional truss structure 80 are configured such that the tensioning members 110 are tensioned and stretched when the truss structure 30 is in the deployed condition. The tensioning members 110 thus apply a constant spring force or tension to the transition truss and compression to the perimeter truss of the truss structure 30 when the truss structure is in the deployed condition. This tension is transferred to the membranes 20 via the catenary cables 100 and the membranes are thus pre-loaded across the truss structure 30.
Those skilled in the art will thus appreciate that, according to the present invention, the membranes 20 become an integral tension transmitting components of the pre-loaded truss structure 30. The deployable structure 10 thus does not require any underlying structure to support the membranes tensioned across the truss structure 30. Tensioned supports upon which to mount the membranes 20, such as a tensioned web, mesh, or matrix, are not required. The membranes 20 themselves are tensioned across the truss structure 30 and are self-supporting.
The catenary cables 100 help to distribute the tension forces applied to the membranes 20. The guides 90 and interfaces 82, being spaced about the periphery 84 of the membranes 20 along the arcs 86, help ensure that the tension forces applied to the membranes are distributed evenly about their peripheries. The catenary cables 100 may be permitted to slide or otherwise move relative to the interfaces 82 and guides 90 and thereby can adjust or respond to the tension applied by the tensioning members 110 to apply tension across the membranes 20 in an even and uniform manner. Alternatively, the catenary cables 100 may be fixed relative to the interfaces 82 and guides 90. The catenary cable 100, in combination with the guides 90 and the interfaces 82, helps prevent the formation of stress risers on the membranes at the locations where the transitional truss structure 80 connects with the membranes 20, i.e., at the interfaces 82. The truss structure 30 thus applies a uniform tension field across the membranes 20. This uniform tension field helps prevent the formation of wrinkles, which can create heat risers, on the membranes 20.
Those skilled in the art will appreciate that the present invention is not limited to the two membrane deployable structure 10 illustrated in FIGS. 1-5. A deployable structure according to the present invention may include more than two membranes. For example, a deployable structure according to a second embodiment of the present invention is illustrated in FIG. 6. The deployable structure of FIG. 6 is similar to the deployable structure illustrated in FIGS. 1-5, except that the deployable structure of FIG. 6 includes four membranes instead of two. Therefore, reference numbers similar to those used in FIGS. 1-5 will be used to identify corresponding components of the deployable structure of FIG. 6, with the suffix “a” added to the reference numbers in FIG. 6 to avoid confusion.
Referring to FIG. 6, the deployable structure 10 a includes membranes 20 a that form a sunshield 22 a. In the embodiment of FIG. 6, there are four membranes 20 a arranged concentric, overlying each other, and spaced apart along a central axis 24 a. The membranes 20 a include a first or inner pair of membranes 150 and a second or outer pair of membranes 160. The inner membrane pair 150 includes first and second membranes 152 and 154, respectively, that are positioned between third and fourth membranes 162 and 164, respectively of the outer membrane pair 160. As shown in FIG. 6, the membranes 162 and 164 of the outer membrane pair 160 may have diameters slightly larger than the membranes 152 and 154 of the inner membrane pair 150 to allow the tensioning members associated with the outer membrane pair to interconnect the membranes 162 and 164 without interference from the first and second membranes 152 and 154.
The membranes 20 a are supported by a truss structure 30 a that includes a perimeter truss structure 40 a, a first transitional truss structure 170, and a second transitional truss structure 180. The perimeter truss structure 40 a is centered on the axis 24 a and encircles the membranes 20 a. The first transitional truss structure 170 is connected to the perimeter truss structure 40 a and to the first and second membranes 152 and 154 at interfaces 156 spaced about the peripheries of the membranes. The second transitional truss structure 180 is connected to the perimeter truss structure 40 a and to the third and fourth membranes 162 and 164 at interfaces 166 spaced about the peripheries of the membranes.
The deployable structure 10 a also includes catenary cables 100 a associated with each membrane 20 a, i.e., a first catenary cable 200 associated with the first membrane 152, a second catenary cable 202 associated with the second membrane 154, a third catenary cable 204 is associated with the third membrane 162, and a fourth catenary cable 206 is associated with the first membrane 164. The deployable structure 10 a further includes tensioning members 110 a, such as springs, that interconnect overlying pairs of the interfaces 156 of the inner membrane pair 150 and that interconnect overlying pairs of the interfaces 166 of the inner membrane pair 160.
The perimeter truss structure 40 a has a configuration, construction, and operation similar or identical to that described above with respect to the perimeter truss structure of the embodiment of FIGS. 1-5. The perimeter truss structure 40 a includes rigid truss members 42 a, including longerons 50 a and battens 60 a, that are interconnected by fittings 44 a. The longerons 50 a define radially stiff, circumferentially extending upper and lower chords 52 a and 54 a, respectively, interconnected by circumferentially spaced, axially stiff battens 60 a. The fittings 44 a permit the longerons 50 a to pivot upward/downward relative to the battens 60 a to allow the truss structure 30 a to move from the non-deployed condition to the deployed condition. The perimeter truss structure 40 a also includes diagonals 70 a that interconnect the fittings 44 a of the upper and lower chords 52 a and 54 a to improve the stability of the perimeter truss structure 40 a.
The membranes 20 a have a configuration and construction similar or identical to that described above with respect to the membranes of the embodiment of FIGS. 1-5. The peripheries of the membranes 20 a are cut or otherwise configured in a series of arcs arranged end-to-end about the periphery, with the interfaces 156, 166 being positioned at each intersection where adjacent arcs meet each other. Between the interfaces, guides (not shown in FIG. 6) are secured to the periphery at spaced locations along the arcs. The guides and interfaces 156, 166 are configured in a manner similar or identical to the guides interfaces of the embodiment of FIGS. 1-5. The catenary cables 100 a extend through and are guided about the respective peripheries of the membranes 20 a and along the arcs by the interfaces 156, 166 and guides.
The transitional truss structures 170 and 180 are constructed and configured in a manner similar or identical to the transitional truss structure of the embodiment of FIGS. 1-5. The tensioning members 110 a extend between and interconnect the interfaces 156, 166 of the first and second membrane pairs 150 and 160. In the deployed condition of the deployable structure 10 a, the tensioning members 110 a apply a constant spring force or tension to the truss structure 30 a when the truss structure is in the deployed condition. This tension is transferred to the membranes 20 a via the catenary cables 100 a and the membranes are thus pre-loaded across the truss structure 30 a. The membranes 20 a are an integral component of the pre-loaded structure. The deployable structure 10 a thus does not require any structure tensioned across the truss structure 30 a, such as a substrate, web, or matrix, upon which to mount the membranes 20 a. The membranes 20 a themselves are tensioned across the truss structure 30 a.
The catenary cables 100 a help to distribute the tension forces applied to the membranes 20 a. The guides and interfaces 156, 166, being spaced about the periphery of the membranes 20 a, help ensure that the tension forces applied to the membranes are distributed evenly about their respective peripheries. The catenary cables 100 a may be permitted to slide or otherwise move relative to the interfaces 156, 166 and guides and thereby can adjust or respond to the tension applied by the tensioning members 110 a to apply tension across the membranes 20 a in an even and uniform manner. Alternatively, the catenary cables 100 a may be fixed relative to the interfaces 156, 166 and guides. The catenary cables 100 a, in combination with the guides and the interfaces 156, 166, help prevent the formation of stress risers on the membranes at the locations where the transitional truss structures 170 and 180 connect with the membranes 20 a, i.e., at the interfaces. The truss structure 30 a thus applies a uniform tension field across the membranes 20 a. This uniform tension field helps prevent the formation of wrinkles, which can create heat risers, on the membranes 20 a.
From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.

Claims

1. A deployable structure comprising:

at least two membranes arranged overlying each other and spaced apart from each other;

a deployable perimeter truss structure encircling the at least two membranes; and

a transition truss structure connecting the membranes to the perimeter truss structure, wherein the perimeter truss structure, transition truss structure, and membranes form a pre-loaded truss structure in which the membranes comprise integral tension transmitting components of the pre-loaded truss structure.

2. The deployable structure recited in claim 1, further comprising:

a catenary associated with each of the at least two membranes, each catenary encircling its associated membrane and being connected to its associated membrane at interfaces spaced about a periphery of the associated membrane; and

tension springs interconnecting adjacent and overlying ones of the interfaces on the at least two membranes.

3. The deployable structure recited in claim 2, wherein the transition truss structure is connected to the interfaces to thereby connect the membranes to the perimeter truss structure.

4. The deployable structure recited in claim 2, wherein each catenary is connected to the interfaces so as to be slidable relative to the associated membrane.

5. The deployable structure recited in claim 2, wherein each catenary is connected to the interfaces so as to be fixed relative to the associated membrane.

6. The deployable structure recited in claim 1, wherein the perimeter truss structure comprises rigid truss members deployable to define a closed periphery centered on a central longitudinal axis of the deployable structure.

7. The deployable structure recited in claim 6, wherein the rigid truss members comprise:

longerons interconnected to form radially stiff first and second peripheral chords centered on the longitudinal axis and spaced apart along the longitudinal axis; and

axially stiff batens extending axially between and interconnecting the first and second peripheral chords.

8. The deployable structure recited in claim 6, wherein the perimeter truss structure further comprises diagonals that interconnect the rigid truss members.

9. The deployable structure recited in claim 2, wherein the transition truss structure comprises at least one cable interconnecting the interfaces on each membrane to the perimeter truss structure.

10. The deployable structure recited in claim 1, wherein the at least two membranes comprise sunshields.

11. The deployable structure recited in claim 1, wherein the at least two membranes comprise a film with an aluminized surface.

12. The deployable structure recited in claim 1, wherein the at least two membranes comprise a polyimide film.

13. The deployable structure recited in claim 2, wherein the springs exert a spring force that urges the interfaces toward each other and tensions the catenaries, which applies a tension across the membranes and through the transition truss to the perimeter truss.

14. The deployable structure recited in claim 2, wherein the springs exerting a spring force that urges the interfaces toward each other places the perimeter truss in compression.

15. The deployable structure recited in claim 13, wherein the catenaries help distribute the tension evenly across the membranes.