Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-01-13
2003-03-18
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C250S491100
Reexamination Certificate
active
06535314
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to satellite communications and more particularly relates to such communications employing optical beams, such as laser beams.
The beams used for space-to-space and space-to-ground optical communications have extremely narrow beam widths that require high bandwidth, closed loop control for pointing and tracking to maintain adequate signal power for communications. The beam widths are so narrow (on the order of 1-20 microradians) that methods are needed to initially acquire the communications beams from the usual 0.1-0.3 degree pointing knowledge uncertainty of current spacecraft. The acquisition method must be highly robust and minimize total weight and power requirements for the optical communications terminal.
Beam acquisition methods have been described in the past. For example, in columns 9-11 and
FIG. 5
, U.S. Pat. No. 3,504,182 (Pizzurro et al., issued Mar. 31, 1970) describes an acquisition method in which a first beam of a first satellite dwells at one point in a field of view while a second beam of a second satellite scans the entire field of view. When the beams illuminate their respective satellites, the acquisition terminates.
U.S. Pat. No. 3,511,998 (Smokler, issued May 12, 1970) describes an acquisition method employing slow oscillatory scan motion limited by limit switches. Receipt of a second beam signal during the slow scan motion terminates the acquisition (Column 11).
U.S. Pat. No. 5,060,304 (Solinsky, issued Oct. 22, 1991) describes an acquisition method relying on beam reflection (Abstract).
U.S. Pat. No. 5,282,073 (Defour et al., issued Jan. 25, 1994) describes an acquisition method in which the width of the beam is altered during acquisition (Columns 5-6).
U.S. Pat. No. 5,475,520 (Wissinger, issued Dec. 12, 1995) describes an acquisition method in which multiple transmitted beams are defocused to provide wide area coverage during acquisition (Column 2).
U.S. Pat. No. 5,592,320 (Wissinger, issued Jan. 7, 1997) describes an acquisition method in which a beam is modulated with time or location information during the acquisition (Column 3).
U.S. Pat. No. 5,710,652 (Bloom et al., issued Jan. 20, 1998) describes an acquisition system employing an array of a CCD acquisition camera (Column 5).
Each of these prior methods and systems have limitations which decrease its usefulness.
BRIEF SUMMARY OF THE INVENTION
One apparatus embodiment of the invention is useful in a communication system employing an optical beam suitable for transmission of data between a first terminal located on an earth orbiting satellite and a second terminal remote from the first terminal. Apparatus on the first terminal aligns the beam received from the second terminal with a beam receptor located on the first terminal within a first uncertainty region which allows tracking of the beam with sufficient accuracy to enable communication of data with the optical beam. According to one embodiment of the invention, the apparatus may include optics enabling receipt of the beam and transmission of the beam along a path. A positioning mechanism is used to point the optics to the location of the second terminal within a second uncertainty region larger than the first uncertainty region. An acquisition sensor receives at least a portion of the beam and locates the second terminal within a third uncertainty region larger than the first uncertainty region and smaller than the second uncertainty region. A controller is responsive to the locating of the second terminal to cause the positioning mechanism to move at least a portion of the optics to successively adjust the position of the beam path relative to the acquisition sensor whereby the size of the third uncertainty region successively approaches the size of the first uncertainty region to facilitate the commencement of tracking of the beam.
A second apparatus embodiment of the invention is useful in a communication system employing an optical beam suitable for transmission of data between a first terminal located on an earth orbiting satellite and a second terminal remote from the first terminal. Apparatus on the first terminal aligns the beam received from the second terminal with a beam receptor located on the first terminal to enable tracking of the beam with sufficient accuracy to enable communication of data with the beam. The apparatus preferably comprises optics receiving the beam and defining a first field of view with a first center point. A positioning mechanism points the optics in the direction of the second terminal. An acquisition sensor defines a second field of view with a second center point receiving at least a portion of the beam and locating the second terminal within a portion of the first field of view. A controller responsive to the locating of the second terminal by the acquisition sensor controls the positioning mechanism successively to point the first and second center points toward a region represented by the portion of the first field of view in which the second terminal is determined to be located until at least a portion of the beam is sufficiently aligned with the beam receptor to enable tracking.
A third apparatus embodiment of the invention is useful in a communication system employing a first optical beam and a second optical beam suitable for transmission of data between a first terminal located on an earth orbiting satellite and a second terminal remote from the first terminal. Apparatus on the first terminal transmits the first beam from the first terminal for alignment with a second beam receptor located on the second terminal and aligns the second beam transmitted by the second terminal with a first beam receptor located on the first terminal within a first uncertainty region which allows tracking of the second beam with sufficient accuracy to enable communication of data with the second beam. Optics in the first terminal enable transmission of the first beam and receipt of the second beam. The optics preferably comprise a beam deflector scanning the first beam over a controlled second uncertainty region with a first scan pattern defining a first locus of scan lines having a center scan line. A positioning mechanism points the optics toward the location of the second terminal and moves the beam deflector. An acquisition sensor in the first terminal receives at least a portion of the second beam and determines the location of the second terminal within a third uncertainty region. A controller in the first terminal successively controls the positioning mechanism in response to the location determined by the acquisition sensor to cause the beam deflector successively to point the center scan line into the third uncertainty region to facilitate the commencement of tracking.
A fourth apparatus embodiment of the invention is useful in a communication system employing a first optical beam and a second optical beam suitable for transmission of data between a first terminal located on an earth orbiting satellite and a second terminal remote from the first terminal. Apparatus on the first terminal transmits the first beam from the first terminal for alignment with a second beam receptor located on the second terminal and aligns the second beam transmitted by the second terminal with a first beam receptor located on the first terminal to enable tracking of the second beam with sufficient accuracy to enable communication of data with the second beam. Optics in the first terminal defines a first field of view having a first center point enabling receipt of the second beam. The optics preferably comprises a beam deflector scanning the first beam over a second field of view having a second center point within the first field of view. A positioning mechanism points the optics toward the location of the second terminal and moves the beam deflector. An acquisition sensor defines a third field of view with a third center point in the first terminal receiving at least a portion of the second beam and determines the location of the second terminal within a portion of the third
Mendenhall Todd L.
Narigon Michael L.
McAndrews Held & Malloy Ltd.
Pascal Leslie
Tran Dzung
TRW Inc.
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