EP0247265A2
Expired / Lapsed
EP
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Star sightings by satellite for image navigation
Assignee: Lanteris Space LLC
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Filing: 1986-12-15
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Granted: —
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Expires: 2006-12-15
Abstract
Abstract Stars are sensed by one or more instruments (1, 2) on board a three-axis stabilized satellite, for purposes of assisting in image navigation. A star acquisition computer (64), which may be located on the earth, commands the instrument mirror (33, 32) to slew just outside the limb of the earth or other celestial body around which the satellite is orbiting, to look for stars that have been cataloged in a star map stored within the computer (64). The instrument (1, 2) is commanded to dwell for a period of time equal to a star search window time, plus the maximum time the instrument (1, 2) takes to complete a current scan, plus the maximum time it takes for the mirror (33, 32) to slew to the star. When the satellite is first placed in orbit, and following first stationkeeping and eclipse, a special operation is performed in which the star-seeking instrument (1, 2) FOV is broadened. The elevation dimension can be broadened by performing repetitive star seeks; the azimuth dimension can be broadened by lengthening the commanded dwell times.
Inventors
- 👤 Ahmed A. Kamel
- 👤 Donald E. Ekman
- 👤 John Savides
- 👤 Gerald Zwirn
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 13:28
CPC Classifications
G; G01; G01C; G01C21/00; G01C21/02; G01C21/025; G09; G09B; G09B9/00; G09B9/02; G09B9/52
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
109 words
A system for assisting in image navigation of a camera on board a satellite, said system comprising: a three-axis stabilized satellite orbiting a celestial body; at least a first camera on board the satellite for gathering data from scenes on the celestial body; means for commanding an optical component of the camera to slew in two orthogonal dimensions to detect stars just beyond the limb of the celestial body; coupled to the camera, means for processing signals produced by the camera in response to star detection, to generate measured star locations; and coupled to the processing means, means for feeding the measured star locations to an image navigation system.
Claim 2
Independent Claim
109 words
A system for assisting in image navigation of a camera on board a satellite, said system comprising: a three-axis stabilized satellite orbiting a celestial body; at least a first camera on board the satellite for gathering data from scenes on the celestial body; means for commanding an optical component of the camera to slew in two orthogonal dimensions to detect stars just beyond the limb of the celestial body; coupled to the camera, means for processing signals produced by the camera in response to star detection, to generate measured star locations; and coupled to the processing means, means for feeding the measured star locations to an image navigation system.
Claim 3
Dependent Claim
42 words
The system of claim 1 wherein the feeding means comprises a model of orbital and attitude parameters and a star map; and the measured star locations comprise the azimuth and elevation, with respect to the camera's optical axes, of each detected star.
Claim 4
Dependent Claim
43 words
The system of claim 1 further comprising a second camera; wherein the first and second cameras independently detect stars; and information determined by said star detection is used by the processing means and feeding means to independently determine the attitude of each camera.
Claim 5
Dependent Claim
45 words
The system of claim 1 wherein the camera gathers the data by scanning across a series of generally parallel scan lines; and an estimate of the satellite's orbit is generated by the feeding means from, inter alia , measurements of stars taken by the camera.
Claim 6
Dependent Claim
128 words
The system of claim 1 wherein the optical component is commanded by the commanding means to dwell at an angular orientation that is fixed with respect to the orbiting satellite, such that the field of view of the optical component includes at least one star from a predetermined catalog of stars stored within the commanding means, for a length of time comprising: the maximum time required by the optical component to complete a current scan and slew to its star sighting position; and a star search window time comprising the time for the target star to pass through the field of view of the optical component, plus a time equivalent to the uncertainty in the knowledge of the exact pointing of the camera, plus a preselected error margin.
Claim 7
Dependent Claim
30 words
The system of claim 1 wherein the celestial body is the earth; and the commanding means, processing means, and feeding means are located in a command station on the earth.
Claim 8
Dependent Claim
48 words
The system of claim 1 wherein the celestial body is the earth; sun and moon ephemeris data is stored within the commanding means; and the commanding means is inhibited from commanding the camera to detect stars when the ephemeris data indicates that sun or moon interference is present.
Claim 9
Dependent Claim
24 words
The system of claim 1 wherein the processing means processes many samples of a star signal produced by the camera for each detected star.
Claim 10
Dependent Claim
76 words
The system of claim 1 in which the commanding means expands the effective star-seeking field of view of the optical component in a first dimension by commanding the optical component to seek more stars than for normal on-orbit operations; and the commanding means expands the field of view of the optical component in a second dimension, orthogonal to the first, by increasing the star-seeking commanded dwell time of the optical component compared with normal on-orbit operations.
Claim 11
Dependent Claim
31 words
The system of claim 9 wherein the field of view expansion is performed as part of a startup initialization during the first day the orbiting camera gathers data from the scenes.
Claim 12
Dependent Claim
59 words
The system of claim 9 wherein the field of view expansion is performed as part of a post-eclipse calibration operation following the first eclipse experienced by the orbiting satellite; and data from said operation is used to compensate for thermal attitude deformations caused by said first eclipse and by subsequent eclipses that occur during the life of the satellite.
Claim 13
Dependent Claim
60 words
The system of claim 9 wherein the field of view expansion is performed as part of a post-stationkeeping calibration operation following the first stationkeeping maneuvers performed by the orbiting satellite; and data from said operation is used to compensate for attitude perturbations caused by said first stationkeeping maneuvers and by subsequent stationkeeping maneuvers performed during the life of the satellite.
Claim 14
Dependent Claim
20 words
The system of claim 1 wherein the measured star locations are determined independently of the magnitudes of the detected stars.
References Cited (Backward Citations)
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