Documentation is presented which is to be used in conjunction with the deposition in the National Space Science Data Center of the unfiltered data obtained during laser ranging operations between the McDonald Observatory and the reflector at Tranquility Base during the interval September 1969 through June 1970

Mulholland, J. D.

English

NASA Technical Reports Server

N 7 2- 25 486 '
Lunar Laser Ranging Data Deposited in the
National Space Science Data Center:
Unfiltered Photon Detections for 1969 September
i through 1970 June
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J. Derral Mulholland
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University of Texas at Austin
Research Memorandum in Astronomy
No. 71-001
1971 September
https://ntrs.nasa.gov/search.jsp?R=19720017836 2020-03-11T18:12:23+00:00Z
I. Introduction
A revolution is occurring in astrometry. Perhaps the
most striking example is the technique of laser ranging to
a reflector fixed on a celestial object, partly because
the attainable precision is so high that the data can tell
us as much about Earth as about the observed object. The
Apollo astronants have now placed three widely separated
reflector arrays on the Moon as a part of the Lunar Laser
Ranging Experiment (LURE), the participants in which are
listed in the Acknowledgements.
Although the groundwork in the experiment began much
earlier, the data-taking process did not begin, of course,
until 1969 July, when the Apollo 11 mission was flown.
Success in recognizing returns from the reflector was not
achieved until the following month. For many months there-
after, various causes contributed to a very low data rate.
It was not until 1970 April that regular successes became
common. ^
From the experiment's inception, the LURE Team has
recognized the obligation to make these data available
in a reasonably usable form, and we have agreed upon a
time-schedule that strives for a fair compromise between
timely release and priority of the members of the LURE
Team. Because of the unforseeable but unsurprising start-
up difficulties in an experiment of this nature, the normal
course of data release is not expected to be proceeding
on this schedule until early 1972. Nonetheless, it seems
desirable to make a preliminary data release at this time.
This report is the documentation to be used in conjunc-
tion with the deposition in the National Space Science
Data Center (NSSDC) of the unfiltered data obtained during
laser ranging operations between the McDonald Observatory
and the reflector at Tranquility Base during the interval
1969 September through 1970 June. It is most important
that the potential user observe.the designation "unfiltered",
By this, we mean that the real data are heavily interspersed
with noise photons from any of the various sources of stray
light. Any attempt to use these data in a simple Gaussian
application would probably result in a solution closely
adhering to the prediction ephemeris used to control the
detector range gating. Some filtering process needs to
be applied to these data before effective use can be made
of them. Such filtering is now underway at the University
of Texas at Austin, and the filtered data will also be
. deposited with NSSDC, but the unfiltered data may be of
direct utility or interest to those potential users who
may wish to replace our filter criteria with their own.
II. Observatory and Reflector
The laser ranging equipment is mounted on the 272 cm
reflector at the McDonald Observatory, Fort Davis, Texas.
The physical installation has been so thoroughly described
in the literature (e.g. Silverberg and Currie 1971) that
it seems unnecessary to dwell on it here. The nominal
coordinates presently recommended for this instrument, based
on high-order land survey ties to the SAO Organ Pass Tracking
Station, are
geocentric radius p = 6374.671 km
east longitude \ = +255.97776 degrees
I geocentric latitude 0T= +30.50316 degrees
!
These refer to the intersection of the polar and transverse
axes of the telescope. The center of the primary mirror,
as the telescope tracks across the sky, describes a circle
of radius 305 cm whose plane is normal to the polar axis.
The present data all refer to the reflector at Tranquility
Base, whose nominal coordinates are
selenpcentric radius p = 1735.567 km
east longitude X = +23.485 degrees
latitude 0 = +0.642 degrees
as supplied by NASA/MSC during tracking operations during the
Apollo 11 mission.
Ill. Data Description and Card Formats
The data are contained on a magnetic tape written in
card image format, through F0RTRAN, using a CDC 6600 computer.
It is written with even parity at 800 bpi. The formats
have been chosen to conform with a currently-proposed
standard (Mulholland 1971) . Two types of cards are present,
distinguished by an alphabetic character in column 1:
The letter Z designates a "run" card, giving environmental
and operational parameters for a series of shots. These
will not customarily be required for application of the
range data, but serve to provide information on the observing
conditions and the state of the equipment. Most users will
find them helpful only as separators between observing
sessions. The letter J^ in column 1 represents a "shot"
card, containing the result of a single laser firing. The
two formats are described below.
Run card
Read a run card with, for example, the F0RTRAN statements
READ (x,l) (A(J),J=1,22)
1 FJ0RMAT(A1,3I,D10.3,1X,I7,I3,3I2,3X, 13,15, 513, AS, 213, 214, 212)
ignoring for the moment that we have mixed our variable modes.
Then the variables A will contain the following information:
A(l) =Z
A (2) =7.11 (3-digit observatory code)
A (3) Julian date of beginning of run
A(4) Clock epoch error, sec x 1Q6
A(5) Ambient temperature, °C
A(6) Ambient relative humidity, % saturation
A(7) Wind speed, km/hr
A (8) Atmospheric seeing, arc sec x 10
A(9) laser energy, joules x 10
A (10) laser frequency, Hg x
A (11) pulse length, sec x
A (12) observational resolution, sec x
A(13) photomultiplier dark count, kHe
A(14) Moon count rate, kHg
A (15) Star count rate, kH«
A (16) Calibration star identification
A(17) Filter spectral width, A x 10
A(18) Filter spatial width, arc sec x 10
A(19) Number of shots fired this run
A(20) Year
A (21) Month
A (2 2) Day
The sense of the clock error is that it is to be subtracted
from the clock time to give the true UTC time. This correction
has not been applied to the observation epochs on the
shot cards.
Shot card
Similarly, again ignoring variable mode questions for the
sake of illustration, read a shot card with
READ (X, 2) (B(J), J=l,17)
2 -F0RMAT (A1,I3,D17.10,15,1X,I1,A1,I1,D12.10,15,16,15,
MX,14,II,15,14,212)
Then the variables B will contain the following information
B(l) =P
B(2) =011 (body identifier)
B (3) Julian date of observation
B(4) =71110 (observatory code)
B(5) =0 (reflector code for Tranquility)
B(6) =L (observation type) -
B (7) =1 (epoch time base is UTC)
B (8) Observed time delay, seconds
B (9) Observational uncertainty, seconds x
B (10) Electronic calibration delay, seconds x
B(ll) Geometric delay, seconds x 1010
B(12) Clock frequency offset from UTC, parts in 1010
B(13) =1 (time delay time base is UTC)
B (14) Ambient pressure, mbar x 10
B(15) Year
B(16) Month . - "
B(17) Day
The electronic and geometric delays refer to the equipment
response times and the reduction to the geometric fixed
point, respectively, and are to be subtracted from the observed
time delay.
A word of warning is in order to the unwary users.
During the report interval, many of the specified data
items discussed above are not available. In the card
images, a blank field is a "no information" indicator.
Actual null values will be represented by zero punches.
This is particularly important for clock epoch error. No
clock data are presently available, although Currie (1970)
estimates that the "actual epoch should be known to the
order of 10 (Jsec or better."
The observational uncertainties are estimates based on
internal consistency and a_ posteriori determination of the
operating characteristics of the electronic systems.
IV. Acknowledgements
The data described herein were generated at the
McDonald Observatory through the collective efforts of the
LURE Team and numerous supporting personnel at their
several institutions. The Team is composed of C.O. Alley
and D.G. Ciirrie (Univ. of Maryland), P.L. Bender (JILA),
R.H. Dicke and D.T. Wilkinson (Princeton Univ.), J.E. Faller
(Wesleyan Univ.), W.M. Kaula (UCLA), G.J.F. MacDonald
(Council on Environmental Quality), J.D. Mulholland and
E.G. Silverberg (McDonald Observatory, Univ. of Texas),
H.H. Plotkin (NASA/GSFC). During the subject interval,
the author's institution was the Jet Propulsion Laboratory.
Preliminary processing of the data described here was done
at the University of Maryland and provided by D.G. Currie
to the author for this purpose. This report and the data
tapes described herein were prepared under NASA Grant
NCR "44-012-219.
V. References
Currie, D.G. 1970, "Report on Lunar Ranging at McDonald
Observatory for the Period December 15, 1969-February
15, 1970': Univ. of Maryland Technical Report 70-090.
Mulholland, J.D. 1971, "Proposed Standards for Distribution
and Documentation of Lunar Laser Ranging Data"
To be published in COSPAR Bulletin.
I
Silverberg, E.G., and Currie, D.G. 1971 "A Description of
, the Lunar Ranging Station at McDonald Observatory"
Space Research XII (in press).


Lunar laser ranging data deposited in the National Space Science Data Center: Unfiltered photon detections for September 1969 through June 1970

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