Quasars can be employed to synchronize global data communications, geophysical measurements, and atomic clocks. It is potentially two to three orders of magnitude better than presently-used Moon-bounce system. Comparisons between quasar and clock pulses are used to develop correction or synchronization factors for station clocks

Goldstein, R. M.

Hurd, W. J.

English

NASA Technical Reports Server

Jnne 1975	 B75-10114 
NASA TECH BRIEF 
NASA Pasadena Office 
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be directed 10 the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Quasars as Very-Accurate Clock Synchronizers 
.
A new system using quasars as a time standard can 
be employed to synchronize global data communica-
tions, geophysical measurements, and atomic clocks. 
It is potentially two to three orders of magnitude 
better than the presently-used Moon-bounce system. 
The pulsed microwave radiation emitted by certain 
radio stars called quasars is recorded at distant 
stations and placed on tapes, together with pulses 
from the station clocks. This information is then sent 
to a central processor where comparisons between the 
quasar and clock pulses are used to develop correction 
or synchronization factors for the station clocks. 
The synchronizer is essentially a very-long baseline, 
radio interferometry system. Since the major opera-
tional costs are data-acquisition time and trans-
mission of the data from the two stations to the 
processing computer, maximum-likelihood estima-
tions are used to minimize the data requirements. 
Thus, in a prototype system, an efficient combination
of high statistical accuracy and a minimal amount of 
data has produced an accuracy of 100 ns. The 
accuracy can be improved by increasing system 
bandwidth until the fundamental limitations due to 
baseline and source-position uncertainties and atmos-
pheric effects are reached. These limitations are 
under 10 ns for transcontinental baselines and 0.1 ns 
may be achievable with extensive calibrations. 
A simplified block diagram of the synchronizer is 
shown in the figure. The quasar signals, which are 
approximately-flat spectrum microwave noise, are 
demodulated in two phase-quadrature channels. The 
signals are then filtered, quantized to a single bit, and 
written onto digital magnetic tape by the control 
computer. The data tapes are then mailed to a 
centrally located computer where the data are 
processed. All of the data-acquisition electronics are 
contained in one small chassis. 
.
Station 
Clock 
Receiver Sampler	 Control 
Signal	 / and (3xlOs Sam Plesj( Computer 
From Demodulator 
/Quasar
Phase-Quadature 
Channels- 
I	 •. 
I
S. 
Known	
_____
Receiver Sampler	 Control 
Time and i1 (3x10' Samples)	 HIIIII'	 Computer Lag Demodulator
Station 
Clock 
Very-Long Baseline; Clock-Synchronization System
Magnetic 
Tape 
Central	 Clock 
Estimate 
Error te Compur 
Magnetic 
Tape
(continued overleaf) 
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In the central computer, the data recordings are 
optimally alined and cross correlated. In a more 
advanced version of the system, the data need not be 
recorded but could be transmitted to the central 
computer over high-speed lines to allow nearly 
real-time processing. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP75- 10114
Patent status: 
NASA has decided not to apply for a patent. 
Source: William J. Hurd and

Richard M. Goldstein of

Caltech/JPL
under contract to

NASA Pasadena Office

(NPO-13276)
is 
Categories: 02 (Electronics Systems) 
03 (Physical Sciences) 
09 (Mathematics and 
B75-10114	 Information Sciences)


Quasars as very-accurate clock synchronizers

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