Communications: radio wave antennas – Antennas – Antenna components
Reexamination Certificate
2000-03-30
2002-08-27
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S912000, C343S840000
Reexamination Certificate
active
06441801
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to energy focusing surfaces, such as radio wave antennas, solar concentrators, and the like and is particularly directed to a screw motion-driven tensegrity support architecture, that is configured to stably deploy and adjustably control characteristics of the energy-focusing surface.
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. As described in the text by Larson and Wertz, entitled “Space Mission Analysis and Design,” Microcosm, Inc., ISBM: 1881883019; November 1992; 2nd Edition, a spacecraft system's requirements may be defined through a process of identifying broad objectives, reasonably achievable goals, and cost constraints. Although space missions vary greatly, and the requirements, goals, and costs associated with each task also vary greatly, one constraint is always present: “space is expensive.”
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, as shown in
FIGS. 1-4
, is configured much like an umbrella. In this type of design, a plurality of radial ribs or segments
1
are connected to a central hub
3
, that supports an antenna feed
5
. A mechanical advantaged linear actuator (not shown) is used to drive the segments
1
from their stowed or unfurled condition, shown in the diagrammatic side and end views of
FIGS. 1 and 2
, into a locked, over-driven, position, so as to deploy a surface
7
, as shown in the diagrammatic side and end views of
FIGS. 3 and 4
. 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.
To meet the above-stated objective, an analysis of mathematics and electrical engineering yields three fundamental parameters of the antenna: 1-defocus, 2-mispointing, and 3-surface roughness. As diagrammatically illustrated in
FIG. 5
, for a receiving antenna, defocus is defined as the error the surface of a reflector
10
that causes the received energy
12
to paint or be projected upon an area
14
, rather than converge onto a focal point (where an antenna feed is placed). As shown in
FIG. 6
, mispointing corresponds to the misplacement of the converged energy
12
to a spatial position
16
other than the designed focal point
18
. The third characteristic—surface roughness (or the approximation of a prescribed (e.g., parabolic) surface geometry), defines the reflector's ability to reflect and collect a given band of RF energy. Higher band reflectors require a more accurate surface that better approximates the theoretical parabola. Conversely, for a transmitting antenna, defocus produces divergent (rather than parallel) waves of energy from the reflector surface, while mispointing directs these waves in the wrong direction.
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.
A relatively comprehensive study of the technology needs for future space systems to be published in the last decade was released by the International Technology Research Institute in a WTEC Panel Report entitled: “Global Satellite Communications Technology and Systems, Executive Summary,” Nov. 11, 1998. This NSF/NASA sponsored research commissioned a panel of U.S. satellite engineers and scientists to study international satellite R&D projects to evaluate the long-term presence of the United States in this industry. A prior study was undertaken in 1992 to establish that there was significant activity in Europe and Asia that rivaled that of the U.S., and benchmarked this R&D to U.S. capability. The later study added market, regulatory, and policy issues in addition to the technology developments. The conclusion was that while the U.S. holds a commanding lead in the space marketplace, there are ongoing gains by both continents. This is evident in space launch, where Ariane Space has nearly achieved the capabilities of Boeing's (Delta) rocket services.
Once significant aspect of this study is that U.S. manufacturers are meeting their goals for short-term research (achieving program performance), but have greatly neglected the long-term goals, which has traditionally been funded by the government. A top candidate technologies include structural elements, materials and structures for electronic devices, and large deployable antennas (having diameters in excess of twenty-five meters). While there have been fourteen meter subsystems developed to meet geosynchronous system requirements during the 1990s, the large deployable requirement has yet to be addressed or developed.
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. As described in the text by P. Tidwell et al, entitled: “Kinematic Analysis of Generalized Adaptive Trusses,” First Joint U.S./Japan Conference on Adaptive Structures, Nov. 13-15, 1990, Technomic Publishing Co., pp. 772-791, 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. Using the
Crane, III Carl David
Duffy Joseph
Knight Byron F.
Rooney Joseph
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
D Chuc Tran
Harris Corporation
Wong Don
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