Method of attitude determination using earth and star sensors
First Claim
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1. A system for determining the 3-axis attitude of a spacecraft in a preselected orbit, comprising:
- star sensing means on said spacecraft for sensing the positions of stars relative to said sensing means, and for producing first signals representing said star positions, said star sensing means including star trackers each having a field of vision aligned in a preselected direction and position with respect to said spacecraft, each of said star trackers including(1) acquiring means for acquiring star position information describing stars within said field of vision.(2) tracking means for tracking said stars within said field of vision.(3) a star catalog.(4) means for identifying said stars within said field of vision using said star position information and said star catalog, and(5) digitizing means for digitizing said star position information into digitized representations of the positions of said stars relative to said spacecraft and said spacecraft orbit, respectively;
terrestrial body sensing means on said spacecraft for sensing the position of a terrestrial body relative to said spacecraft, and for producing second signals representing said terrestrial body position; and
processing means for processing said first and second signals and for determining said 3-axis attitude of said spacecraft.
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Abstract
A method of attitude measurement for an artificial satellite (100) utilizes one or more star trackers (12) together with an earth sensor (30). Periodic updates of satellite orbital information, either propagated onboard or from a ground station are combined with earth and star position coordinate data to provide a continuous and accurate measurement of the spacecraft body 3-axis attitude. The method can be used for ground-based attitude determination or onboard closed loop control systems.
65 Citations
31 Claims
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1. A system for determining the 3-axis attitude of a spacecraft in a preselected orbit, comprising:
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star sensing means on said spacecraft for sensing the positions of stars relative to said sensing means, and for producing first signals representing said star positions, said star sensing means including star trackers each having a field of vision aligned in a preselected direction and position with respect to said spacecraft, each of said star trackers including (1) acquiring means for acquiring star position information describing stars within said field of vision. (2) tracking means for tracking said stars within said field of vision. (3) a star catalog. (4) means for identifying said stars within said field of vision using said star position information and said star catalog, and (5) digitizing means for digitizing said star position information into digitized representations of the positions of said stars relative to said spacecraft and said spacecraft orbit, respectively; terrestrial body sensing means on said spacecraft for sensing the position of a terrestrial body relative to said spacecraft, and for producing second signals representing said terrestrial body position; and processing means for processing said first and second signals and for determining said 3-axis attitude of said spacecraft. - View Dependent Claims (2, 3)
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4. A spacecraft attitude control system for determining the 3-axis attitude of a spacecraft in a preselected orbit, consisting essentially of:
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star sensing means on said spacecraft for sensing the positions of stars relative to said sensing means, and for producing first signals representing said star positions; cross-link sensing means on said spacecraft for sensing the position of a preselected RF beacon relative to said spacecraft, and for producing second signals representing said beacon position; and processing means for processing said first and second signals and for determining said 3-axis attitude of said spacecraft. - View Dependent Claims (5, 6)
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7. A method of determining the three axis attitude of a spacecraft in a preselected orbit, using star trackers on said spacecraft, an on-board star catalog and terrestrial sensor on said spacecraft, comprising the steps of:
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(A) measuring the position of a terrestrial body with respect to said spacecraft, using said terrestrial sensor; (B) generating a first set of coordinate data using said orbit, said first set of coordinate date defining the position of said terrestrial body relative to said spacecraft orbit; (C) measuring the positions of each of a plurality of stars with respect to said star trackers, using said star trackers; (D) generating a second set of coordinate data using the positions measured in step (C), said second set of coordinate data defining the positions of said stars relative to said spacecraft; (E) identifying each star measured in step (C), using said star trackers and said on-board star catalog, to generate a third set of coordinate data, said third set of coordinate data defining the positions of said stars relative to said spacecraft orbit; and (F) determining said attitude of said spacecraft using the position measured in step (A) and the first, second and third sets of coordinate data respectively generated in steps (B), (D) and (E). - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method of determining the three axis attitude of a spacecraft in a preselected orbit, using star trackers on said spacecraft, an on-board star catalog and a terrestrial sensor on said spacecraft, comprising the steps of:
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(A) measuring the position of a terrestrial body with respect to said spacecraft, using said terrestrial sensor by measuring the nadir of said terrestrial body; (B) generating a first set of coordinate data using information regarding said spacecraft orbit and a second set of coordinate data, said second set of coordinate data having an almanac of the position of said terrestrial body relative to time, said first set of coordinate data defining the position of said terrestrial body relative to said spacecraft orbit; (C) measuring the positions of each of a plurality of stars with respect to said star trackers, using said star trackers by acquiring and tracking said plurality of stars as said stars pass through the field of vision of said star trackers; (D) generating a third set of coordinate data using the positions measured in step (C) by transforming a fourth set of coordinate data into said third set of coordinate data, said fourth set of coordinate data defining the positions measured in step (C), said third set of coordinate data defining the positions of said stars relative to said spacecraft; (E) identifying each star measured in step (C), using said star tracker and said on-board star catalog by tracking said stars and comparing tracking information to information contained in said star catalog; (F) generating a fifth set of coordinate data using the identification of each star from (E), said fifth set of coordinate data defining the positions of said stars relative to said spacecraft orbit; (G) averaging and normalizing the third set of coordinate data in step (D) to determine a single averaged and normalized representation of said third set of coordinate data; (H) averaging and normalizing the fifth set of coordinate data in step (F) to determine a single average and normalized representation of said fifth set of coordinate data; (I) defining a set of spacecraft attitude variables in terms of said measurement from step (A) and said first, third and fifth sets of coordinate data, said attitude variables defining the roll pointing error, the pitch pointing error, and the yaw pointing error of said spacecraft, respectively; (J) forming a system of equations using said set of spacecraft attitude variables and said averaged and normalized representations of said third and fifth sets of coordinate data in steps (G) and (H), respectively; (K) determining a set of value data for said attitude variables by solving the system of equations in step (J); and (L) determining said attitude of said spacecraft from the set of value data in step (K). - View Dependent Claims (22, 23, 24, 25, 26, 27, 28)
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29. A system for determining the 3-axis attitude of a spacecraft in a preselected orbit, comprising:
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star sensing means on said spacecraft for sensing the position of stars relative to said sensing means, and for producing first signals representing said star positions; earth sensing means on said spacecraft for sensing the position of the earth relative to said spacecraft, and for producing second signals representing said earth position, said earth sensing including a carbon dioxide band sensor for measuring the position of said earth relative to said spacecraft by measuring the nadir of the earth, said earth sensing producing said first signals, said first signals being digitized representations of said earth position relative to said spacecraft and said spacecraft orbit, respectively; and
,processing means for processing said first and second signals and for determining said 3-axis attitude of said spacecraft.
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30. A system for determining the 3-axis attitude of a spacecraft in a preselected orbit, comprising:
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star sensing means on said spacecraft for sensing the position of said stars relative to said sensing means, and for producing first signals representing said star positions; and earth sensing means on said spacecraft for sensing the position of the earth relative to said spacecraft, and for producing second signals representing said earth position, said earth sensing means comprising RF ground beacon sensor for measuring the position of the earth relative to said spacecraft measuring the azimuth and elevation of a preselected ground station having known longitude and latitude location values on said earth, said earth sensing means producing said first signals that are digitized representations of said earth position relative to said spacecraft and said spacecraft orbit, respectively.
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31. A system for determining the 3-axis attitude of a spacecraft in a preselected orbit, comprising:
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star sensing means on said spacecraft for sensing the positions of stars relative to said sensing means, and for producing first signals representing said star positions; terrestrial body sensing means on said spacecraft for sensing the position of a terrestrial body relative to said spacecraft, and for producing said second signals representing said terrestrial body position; and
,processing means for processing said first and second signals for determining said 3-axis attitude of said spacecraft, said processing means including (1) collecting and averaging means for collecting and averaging said first and second signals, and, (2) estimating means for estimating a set of attitude variables using the least squares approximations of said attitude variables, said attitude variables defining said 3-axis attitude of said spacecraft.
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Specification