Satellite clock system

A method for correcting error in an onboard satellite clock, comprising the steps of:

• transmitting metering bursts from an earth station to a satellite;
• determining, in accordance with re-transmitted bursts received from said satellite, an amount of error in an onboard clock of said satellite which occurs over a first time interval which is a sidereal day multiple;
• and
• transmitting to said satellite a correction value for correcting said error in said onboard clock.

A satellite clock system comprising:

• a high-stability, low-uncertainty reference oscillator;
• a programmable divider receiving a clock input from said oscillator;
• means for transmitting metering bursts to a satellite in response to an output signal from said programmable divider;
• means for measuring an amount of phase error in received metering bursts re-transmitted from said satellite, an output signal from said phase error measuring means being coupled to a control input port of said programmable divider;
• a first accumulator receiving an input said output signal from said phase error measuring means;
• a second accumulator receiving an input from an output of said first accumulator;
• an adder receiving inputs from outputs of said first accumulator and said second accumulator;
• means for multiplying an output of said adder by a fixed value;
• a third accumulator receiving an input from an output of said multiplier;
• and
• means for telemetering an output of said third accumulator to a satellite, said output of said third accumulator being utilized by said satellite as an input control value of a voltage-controlled oscillator onboard reference clock.

A satellite clock system comprising:

• a high-stability, low-uncertainty reference oscillator;
• a programmable divider receiving a clock input from said oscillator;
• means for transmitting metering bursts to a satellite in response to an output signal from said programmable divider;
• means for measuring an amount of phase error in received metering bursts re-transmitted from said satellite, an output signal from said phase error measuring means being coupled to a control input port of said programmable divider;
• a first accumulator receiving as an input said output signal from said phase error measuring means;
• a second accumulator receiving an input from an output of said first accumulator;
• an adder receiving inputs from outputs of said first accumulator and said second accumulator;
• means for multiplying an output of said adder by a fixed value;
• means for telemetering an output of said second accumulator to a satellite, said output of said second accumulator being accumulated on a sidereal day basis and utilized by said satellite as an input control value of a voltage-controlled oscillator onboard reference clock.

A method for correcting error of an onboard satellite clock, comprising the steps of:

• transmitting metering bursts from an earth station to a satellite, said metering bursts being timed with pulses produced by a high stability, low-uncertainty reference oscillator divided in frequency by a programmable divider, each said metering burst containing a predetermined pattern of symbols;
• comparing the pattern of symbols in received bursts re-transmitted from said satellite with a stored pattern of said predetermined symbols;
• computing an average number of incorrect comparisons between received bursts re-transmitted from said satellite and said stored pattern to determine a value corresponding to a time amount of misalignment between transmitted metering bursts and a synchronization window of said satellite, said value being applied to a control input port of said programmable divider;
• accumulating values corresponding to the time amount of misalignment between said metering bursts and said synchronization window over a predetermined period of time to determine a current accumulated phase shift value;
• accumulating current values of said phase shift value from the beginning of system operation to the current time to provide a cumulative phase shift value;
• summing said current phase shift value and said cumulative phase shift value to provide a predicted phase correction;
• dividing the sum of said current phase shift value and said cumulative phase shift value by a value representative of said predetermined period of time;
• accumulating output values determined as a result of said division at said predetermined period of time from the beginning of system operation to provide a cumulative frequency correction value;
• and
• telemetering said cumulative frequency correction value to said satellite, said cumulative frequency value received in said satellite being used to set an output frequency of a voltage-controlled oscillator in said satellite which forms an onboard clock of said satellite.