Satellite clock system

Details Satellite clock system Satellite clock system

1982-06-14

1988-12-20

Safourek, Benedict V.

Pulse or digital communications

Spread spectrum

Direct sequence

455 12, 370104, H03K 117, H04L 700

Patent

active

047929634

ABSTRACT:
A satellite clock system in which the frequency of the onboard satellite clock, which is implemented as a relatively high uncertainty voltage-controlled oscillator, is corrected in accordance with a high-stability, low-uncertainty terrestrial clock. Metering bursts are transmitted from the earth station to the satellite where portions of the metering bursts are truncated due to misalignment between the bursts and the synchronization windows timed by the onboard oscillator of the satellite. The patterns of the received bursts which are re-transmitted by the satellite are compared with a stored pattern and a phase shift value determined in accordance with the number of incorrect comparisons. The phase error measurement value is utilized to control a programmable divider connected between the high-stability, low-uncertainty oscillator and the burst transmitter to thus provide a short-term correction. The output values from the phase error measurement are accumulated over a sidereal day period to provide a sidereal day phase shift value. The accumulated value of the sidereal day phase shifts is summed with all previous daily values to compute a cumulative phase shift from the beginning of the system operation. The current and cumulative phase shift values are then summed and divided by a period of one sidereal day to produce an actual phase correction for the next sidereal day. The actual daily frequency correction is computed by summing all values of the sidereal day frequency correction and telemetering this value to the satellite. Alternately, the accumulation of the frequency corrections can be performed onboard the satellite.

REFERENCES:
patent: 3562432 (1971-02-01), Gabbard
patent: 3596002 (1971-07-01), Ohnsorge
patent: 3995111 (1976-11-01), Tsuji et al.
patent: 4004098 (1977-01-01), Shimasaki
patent: 4215348 (1980-07-01), Cordaro et al.
patent: 4320503 (1982-03-01), Acampora
patent: 4413282 (1983-11-01), Wargo
patent: 4435825 (1984-03-01), Tomooka
Campanella et al "On Board Clock Correction for SS/TDMA and Baseband Processing Satellites" Comsat Tech Rev (USA) vol. 11 No. 1 (Spring 1981) pp. 77-102-77-101.

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