A high radiance, pulsed laser system with a transportable transmitting unit was used to measure the transit times of 25 ns, 10 joule, and 530 nm pulses from earth to the Apollo 15 retroreflector on the moon and back

Criswell, S. J.

Lehr, C. G.

Mulholland, J. D.

Ouellette, J. P.

Shelus, P. J.

Sozanski, P. W.

English

NASA Technical Reports Server

LASER TRANSIT-TIME MEASUREMENTS _BETWEEN._
EARTH AND MOON WITH A TRANSPORTABLE SYSTEM
C. G. Lehr, S. J. Criswell, J. P. Ouellette, P. W. Sozanski,
J- D. Mulholland, and P. J. Shehis
C
COPY
January 1973
Smithsonian Institution
Astrophysical Observatory
Cambridge, Massachusetts 02138
"2T2R792"
https://ntrs.nasa.gov/search.jsp?R=19730009775 2020-03-23T07:02:48+00:00Z
Laser Transit-Time Measurements between
Earth and Moon with a Transportable System
Abstract. A high-radiance, pulsed laser system with a transportable transmitting
unit was used at Agassiz Station, Harvard College Observatory, Harvard, Massachusetts,
to measure the transit times of 25-ns, 10-joule, 530-nm pulses from Earth to the
Apollo 15 retroreflector on the Moon and back.
On 23 September 1972, the transit time of a laser pulse from Earth to Moon and
back was measured six times at Agassiz Station, Harvard College Observatory,
Harvard, Massachusetts.
The laser pulse was directed to the Apollo 15 retroreflector on the Moon by a
transportable transmitting unit located 237 m from the 1. 5-m telescope used to detect
the returning pulse. All six transit times were measured with a combination of delay
circuits and a fast oscilloscope. Three of these returns, which were stronger than
the rest, were also measured more precisely with a time-interval counter.
Residuals for all the measured transit times were calculated from a special
ephemeris at the University of Texas (1). These residuals (observed values minus
computed values) tended to increase with epoch (time of transmission of the laser
pulse) oviE
obtained.
ver the period from 6 36m to 8 12m universal time during which they were
The best-fitting straight line through the residuals from the counter readings had
a slope of +0. 35 ns/min with a standard deviation of 3.1 ns. The best line through
212—002
the residuals of the six oscilloscope readings had a slope of +0.18 ns/min with a
standard deviation of 2. 5 ns. The differences in the results from the two sets of data
are not significant.
The slope of the straight line through the residuals is related to the error in the
station's geocentric coordinates. If one assumes the error to be entirely in latitude,
the local hour angle of these observations implies that a slope of 1 ns/min corresponds
to 1 arcsec, ~or"23 m at the"station's"42?5~latitude.~ Hence; the slopes"are consistent
with an error of about 15 m expected in the conversion of the station's coordinates
from the North American Datum to a geocentric system.
The configuration of the transportable laser system, which can be used with other
large telescopes, has been described previously (2). The exceptionally high radiance
of the system's neodymium-glass laser permits the use of a transmitting telescope
whose aperture diameter is only 0 .2m. It also increases the probability that each
return generates at least one photo electron. The system's pulse repetition rate is
0. 2/min. A further report on its operation is in preparation (3).
This work was supported in part by contract NASW-2014 and grant NCR 44-012-219
from the National Aeronautics and Space Administration.
C. G. Lehr, S. J. Criswell, J. P. Ouellette, P. W. Sozanski
Smithsonian Astrophysical Observatory
Cambridge, Massachusetts 02138
J. D. Mulholland, P. J. Shelus
Department of Astronomy, The University
of Texas, Austin, Texas 78712
References and Notes
1. This ephemeris, not yet described in the literature, is a numerical integration
fit to both optical and laser data. It was developed by J. D. Mulholland and
P. L. Bender (JILA) as a part of the Apollo Lunar-Laser Ranging Experiment.
2. C. G. Lehr, M. R. Pearlman, J. A. Monjes, W. F. Hagen, Appl. Opt. 11,
300 (1972).
3. C. G. Lehr, J. P. Ouellette, P. W. Sozanski, J. T. Williams, S. J. Criswell,
and M. Mattei, Appl. Opt., Letter to the Editor, in preparation.
The authors acknowledge with appreciation and thanks the cooperation and efforts
of the following persons: L. DiPalma, J. T. Williams, and J. Wohn (Smithsonian
Astrophysical Observatory); W. Liller and M. Mattei (Harvard College Observatory);
D. H- Eckhardt (Air Force Cambridge Research Laboratory); J. G. Williams (Jet
Propulsion Laboratory); E. C. Silverberg (McDonald Observatory); and C. O. Alley
(University of Maryland).


Laser transit-time measurements between earth and moon with a transportable system

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