RF link control of satellite clocks
First Claim
1. A method for maintaining a time standard among a plurality of orbiting satellites, each of said satellites including at least one timing reference, comprising the steps of:
- crosslinking said satellites with communication crosslinks in order that said satellites can communicate with each other;
transmitting timing reference data across said communication crosslinks to communicate said data among said satellites, said satellites processing said timing reference data in a predetermined manner to produce a set of ensemble timing references at said satellites, whereby the deviation among said ensemble timing references is less than the deviation among said timing references;
transmitting said ensemble timing references from said satellites to a location where a time standard is maintained;
deriving an offset between said transmitted ensemble timing references and said time standard;
transmitting said offset from said location to said satellites, wherein only a predetermined number of said satellites receive said offset from said location;
transmitting said offset, received by said predetermined number of said satellites said satellites, across said communication cross links to said satellites which did not receive said offset from said location; and
using said offset to lock said ensemble timing references to said time standard, thereby creating a corrected system time.
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Accused Products
Abstract
A system and method for maintaining a precise time standard among a system of orbiting satellites is disclosed. In an illustrative embodiment, atomic clock data is circulated among the satellites via RF crosslinks. Each satellite uses the received data as input to a Kalman process which acts to minimize the mean squared error among the satellite clocks to form a set of "ensemble clocks". The resulting ensemble clock values are then transmitted to an earth station where an offset between the ensemble clocks and Universal Time is computed. The offset is transmitted from the earth station to the satellites where it is used by the satellites to lock their on-board clocks to Universal Time, thereby creating a corrected system time. The corrected system time is transmitted, via RF crosslinks, to satellites not having operational on-board clocks. The satellites without atomic clocks employ phase locked loops to anchor their clocks to the corrected system time as it is received over the crosslinks.
47 Citations
20 Claims
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1. A method for maintaining a time standard among a plurality of orbiting satellites, each of said satellites including at least one timing reference, comprising the steps of:
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crosslinking said satellites with communication crosslinks in order that said satellites can communicate with each other; transmitting timing reference data across said communication crosslinks to communicate said data among said satellites, said satellites processing said timing reference data in a predetermined manner to produce a set of ensemble timing references at said satellites, whereby the deviation among said ensemble timing references is less than the deviation among said timing references; transmitting said ensemble timing references from said satellites to a location where a time standard is maintained; deriving an offset between said transmitted ensemble timing references and said time standard; transmitting said offset from said location to said satellites, wherein only a predetermined number of said satellites receive said offset from said location; transmitting said offset, received by said predetermined number of said satellites said satellites, across said communication cross links to said satellites which did not receive said offset from said location; and using said offset to lock said ensemble timing references to said time standard, thereby creating a corrected system time. - View Dependent Claims (2, 3, 4, 5)
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6. A method for maintaining a time standard among a plurality of orbiting satellites, said plurality of orbiting satellites comprising a first set of satellites, wherein each satellite includes at least one timing reference, and a second set of satellites, wherein each satellite includes a timing means, comprising the steps of:
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crosslinking said first set of satellites, said second set of satellites, and said first and second set of satellites, with communication crosslinks in order that said satellites can communicate with each other; transmitting timing reference data across said communication crosslinks to communicate said data among said first set of satellites and processing said timing reference data in a predetermined manner to produce a set of ensemble timing references for said first set of satellites, whereby the deviation among said ensemble timing references is less than the deviation among said timing references of said first set of satellites; transmitting said ensemble timing references from said first set of satellites to a location where a time standard is maintained; deriving an offset between said transmitted ensemble timing references and said time standard; transmitting said offset from said location to said first set of satellites, wherein only a predetermined number of said first set of satellites receive said offset from said location; transmitting said offset, received by said predetermined number of said first set of satellites, across said communication crosslinks to said first set of satellites which did not receive said offset from said location; using said offset to lock said ensemble timing references of said first set of satellites to said time standard, thereby creating a corrected system time; providing a phase locked loop in each satellite of said second set of satellites; transmitting said corrected system time across said communication crosslinks from said first set of satellites to each satellite of said second set of satellites; and using said corrected system time in combination with said phase locked loops to lock said timing means of said second set of satellites to said corrected system time. - View Dependent Claims (7, 8, 9, 10)
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11. An RF Link Control apparatus for maintaining a time standard among a plurality of orbiting satellites, each of said satellites including at least one timing reference, comprising:
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means for computing an ensemble timing reference at each of said satellites, whereby the deviation among said ensemble timing references is less than the deviation among said timing references; means for transmitting said ensemble timing references from said satellites to a location where a time standard is maintained, said ensemble timing references to be used at said location to derive an offset between said ensemble timing references and said time standard; means for transmitting said offset from said location to said satellites; means for generating a steering signal from said offset, said steering signal to be used at said satellites to lock said ensemble timing references to said time standard, thereby creating a corrected system time; and a plurality of communication crosslinks between said satellites for transferring timing reference data among said satellites. - View Dependent Claims (12, 13, 14, 15)
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16. An RF Link Control apparatus for maintaining a time standard among a plurality of orbiting satellites, said plurality of orbiting satellites comprising a first set of satellites, wherein each satellite includes at least one timing reference, and a second set of satellites, wherein each satellite includes at least one timing means, comprising:
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means for computing an ensemble timing reference at each satellite of said first set of satellites, the deviation among said ensemble timing references is less than the deviation among said timing references; means for transmitting said ensemble timing references from each satellite of said first set of satellites to a location where a time standard is maintained, said ensemble timing references to be used at said location to derive an offset between said ensemble timing references and said time standard; means for transmitting said offset from said location to said first set of satellites; means for generating a steering signal from said offset, said steering signal to be used at said first set of satellites to lock said ensemble timing references to said time standard, thereby creating a corrected system time; a first plurality of communication crosslinks between said satellites of said first set, a second plurality of communication crosslinks between said satellites of second set and a third plurality of communication crosslinks between said first and second sets of said satellites, for transferring timing reference data among said satellites; and means for locking said timing means of said second set of satellites to said corrected system time. - View Dependent Claims (17, 18, 19, 20)
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Specification