Communications: radio wave antennas – Antennas – Antenna components
Reexamination Certificate
2001-06-12
2003-04-01
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S880000
Reexamination Certificate
active
06542132
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to radio wave antennas, and, more particularly, to deployable antennas including tensegrity support architecture.
BACKGROUND OF THE INVENTION
The field of deployable structures, such as space-deployed platforms, has matured significantly in the past decade. What once was a difficult art to master has been developed into a number of practical applications by commercial enterprises. The significance of this maturity has been the reliable deployment of various spacecraft-supported antenna systems, similar to that employed by the NASA tracking data and relay satellite (TDRS). In recent years, the development of parabolic, mesh-surface, reflector geometries has been accompanied by improvements in phased arrays (flat panel structures with electronically steered beams), both of which are critical to commercial and defense space programs. As commercial spacecraft production has exceeded military/civil applications, there is currently a demand for structural systems with proven reliability and performance, and the ever present reduced cost.
The mission objective for a large, deployable space antenna is to provide reliable radio frequency (RF) energy reflection to an electronic collector (feed) located at the focus of the parabolic surface. The current state of deployable parabolic space antenna design is principally based on what may be termed a segmented construction approach which is configured much like an umbrella. In this type of design, a plurality of radial ribs or segments are connected to a central hub, that supports an antenna feed. A mechanical advantaged linear actuator is used to drive the segments from their stowed or unfurled condition into a locked, over-driven, position, so as to deploy a surface. A shortcoming of a single fold design of this type of antenna is the fact that the height of the stowed package is over one half of the deployed diameter. Other proposals include the use of hoop tensioners and mechanical memory surface materials.
In recent years, numerous Defense Department organizations have solicited for new approaches to deployable antenna structures. The Air Force Research Laboratories (AFRL) are interested in solutions to aid with their Space Based Laser and Radar programs, and have requested new solutions to building precision deployable structures to support the optical and radar payloads. These requests are based upon the premise that the stowed density for deployable antennas can be significantly increased, while maintaining the reliability that the space community has enjoyed in the past. A failure of these structures is unacceptable. If the stowed volume can be reduced (therefore an increase in density for a given weight), launch services can be applied more efficiently.
The implementation of multiple vehicle launch platforms (e.g., the Iridium satellite built by Motorola) has presented a new case where the launch efficiency is a function of the stowed spacecraft package, and not the weight of the electronic bus. For extremely high frequency (EHF) systems (greater than 20 GHz) in low earth orbit (LEO), the antenna aperture needs to be only a few meters in diameter. However, for an L-band, geosynchronous orbit satellite (such AceS built by Lockheed Martin), the antenna aperture diameter is fifty feet. Less weight and payload drag must be achieved to ensure a more efficient assent into a geosynchronous orbit.
Tetrobots have been developed in the last few years as a new approach to modular design. The tetrobot approach, which is described in the text by G. Hamlin et al, entitled: “TETROBOT, A Modular Approach to Reconfigurable Parallel Robotics,” Kluwer Academic Publishers, 1998 (ISBN: 0-7923-8025-8) utilizes a system of hardware components, algorithms, and software to build various robotic structures to meet multiple design needs. These structures are Platonic Solids (tetrahedral and octahedral modules), with all the connections made with truss members. Adaptive trusses have been applied to the field of deployable structures, providing the greatest stiffness and strength for a given weight of any articulated structure or mechanism.
The most complex issue in developing a reliable deployable structure design is the packaging of a light weight subsystem in as small a volume as possible, while ensuring that the deployed structure meets system requirements and mission performance. An article by D. Warnaar, entitled: Evaluation Criteria for Conceptual of Deployable-Foldable Truss Structures,” ASME Design Engineering: Mechanical Design and Synthesis, Vol. 46, pp. 167-173, 1992, in describing criteria developed for deployable-foldable truss structures, addresses the issues of conceptual design, storage space, structural mass, structural integrity, and deployment. This article simplifies the concepts related to a stowed two-dimensional area deploying to a three-dimensional volume. A tutorial on deployable-foldable truss structures is presented in: “Conceptual Design of Deployable-Foldable Truss Structures Using Graph Theory-Part 1: Graph Generation,” by D. Warnaar et al, ASME 1990 Mechanisms Conference, pp. 107-113, September 1990, and “Conceptual Design of Deployable-Foldable Truss Structures Using Graph Theory-Part 2: Generation of Deployable Truss Module Design Concepts, by D. Warnaar et al, ASME, 1990 Mechanisms Conference, pp. 115-125, September 1990. This series of algorithms presents a mathematical representation for the folded (three-dimensional volume in a two-dimensional area) truss, and aids in determining the various combinations for a folded truss design.
NASA's Langley Research Center has extensive experience in developing truss structures for space. One application, a 14-meter diameter, three-ring optical truss, was designed for space observation missions. An article by K. Wu et al, entitled: “Multicriterion Preliminary Design of a Tetrahedral Truss Platform,” Journal of Spacecraft and Rockets, Vol. 33, No. 3, May-June 1996, pp. 410-415, details a design study that was performed using the Taguchi methods to define key parameters for a Pareto-optimal design: maximum structural frequency, minimum mass, and the maximum frequency to mass ratio. In the study, tetrahedral cells were used for the structure between two precision surfaces. 31 analyses were performed on 19,683 possible designs with an average frequency-to-mass ratio between 0.11 and 0.13 Hz/kg. This results in an impressive 22 to 26 Hz for a 200-kg structure.
The field of deployable space structures has proven to be both technically challenging and financially lucrative during the last few decades. Such applications as large parabolic antennas require extensive experience and tooling to develop, but is a key component to the growing personal communications market. Patents relating to deployable space structures have typically focused on the deployment of general truss network designs, rather than specific antenna designs. Some of these patents address new approaches that have not been seen in publication.
For example, the U.S. patents to Kaplan et al, U.S. Pat. No. 4,030,102, and Waters et al, U.S. Pat. No. 4,825,225 describe the application of strut and tie construction to deployable antennas. However, the majority of patents address trusses and the issues associated with their deployment and minimal stowage volume. For example, the U.S. patent to Nelson U.S. Pat. No. 4,539,786 describes a design for a three-dimensional rectangular volume based on an octahedron. Deployment uses a series of ties within the truss network, and details of the joints and hinges are described. When networked with other octahedral subsets, a compact stow package could be expanded into a rigid three-dimensional framework.
Other patents describe continued work in expandable networks to meet the needs of International Space Station. For example, the U.S. patent to Natori U.S. Pat. No. 4,655,022, employs beams and triangular plates to form tetrahedral units that provide a linear truss. The patent details both joint and hinge details and the stowage and dep
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Harris Corporation
Wimer Michael C.
LandOfFree
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