The technique of laser ranging to a reflector fixed on the lunar surface is discussed. The causes for initial low rate of data acquisition are explained. The documentation to be used in conjunction with the deposition of the filtered data in the National Space Science Data Center are documented. Filtered data obtained during laser operations between the McDonald Observatory and the reflector at Tranquility Base during the interval September 1969 through June 1970 are presented. The unfiltered photon detections for the succeeding six months are examined

Mulholland, J. D.

Shelus, P. J.

Terrell, K.

English

NASA Technical Reports Server

Lunar Laser Ranging Data Deposited in the
National Space Science Data Center:
Filtered Observations for 1969 September through 1970 June
and
Unfiltered Photon Detections for 1970 July through December
J. Derral Mulholland
JPeter J. Shelus
Karen Terrell
University of Texas at Austin
Research Memorandum in Astronomy
No. 72-003
1972 January
https://ntrs.nasa.gov/search.jsp?R=19720022795 2020-03-11T19:33:52+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 preci-
sion 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 present
submission is the first to achieve the normal schedule. This
report is the documentation to be used in conjunction with the
deposition in the National Space Science Data Center (NSSDC) of
the filtered data obtained during laser ranging operations between
the McDonald Observatory and the reflector at Tranquility Base during
the interval 1969 September through 1970 June and the unfiltered
photon detections for the succeeding six months. These two blocks
will be discussed in more detail in subsequent sections of this
memorandum.
II. Observatory and Reflector
The laser ranging equipment is mounted on the 272 cm reflector
at the McDonald Observatory, Fort Davis, Texas. The physical instal-
lation 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 A.=+255 .97776 degrees
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
selenocentric radius p=1735.567 km
east longitude X=+23.485 degrees
latitude 3=+0.6M-2 degrees
as supplied by NASA/MSC during tracking operations during the
Apollo 11 mission.
III. Filtered Data
The photon detections for 1969 September through 1970 June have
been submitted to a data filtering procedure developed at the
University of Texas. This process is based on the assumption of
the linearity of 0-C residuals over a relatively short time interval
and relies on Poisson statistics for establishing a level of con-
fidence in a collection identified by the filter. Application of
the process resulted in the identification of 120 observations
during the subject interval. Additional points may be added to
this set later, as some of the early operations were recorded on
paper tape, and the corresponding photon detections are not yet
available to us.
The potential user should be aware that the laser cannot be
relied upon to produce a simple pulse shape. There sometimes is
a complex and/or biased structure within the pulse. Therefore,
residuals derived from signal photons are not necessarily expected
to show a Gaussian distribution.
The observational uncertainties for data prior to 1970 March
16 are arbitrarily degraded to a high level, reflecting the discovery
of severe electronic problems that caused apparently irrecoverable
timing errors during this period. The uncertainties assigned
subsequent to that date are based on the sum of the pulse half-
width and the measured uncertainty in calibrating the electronic
system. The calibrations were performed by E.G. Silverberg.
IV. Unfiltered Photon Detections
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 in 1972
July, 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.
V. Data Description and Card Formats
The data are contained on a magnetic tape written in card
image format, through FJ0RTRAN, 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 Fj0RmT(Al,3I,D10.3,lX, I7,I3,3I2,3X, I3,I5,5I3,A5,2I3,2I4, 212)
ignoring for the moment that we have mixed our variable modes.
Then the variables A will contain the following information:
A CD =z
A (2) =711 (3-digit observatory code)
A (3) Julian date of beginning of run
A (4) Clock epoch error, sec x 106
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, Ha x lO^-O
A (11) pulse length, sec x IQlO
A (12) observational resolution, sec x
A (13) photomultiplier dark count, kite
A (14) Moon count rate, kHe (Gross)
A (15) Star count rate, kHe (Net)
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 (22) 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)
3X IS"
2 F0RMAT (Al, I3,D17 .10, 15, IX, II, Al, I1,D12 .10, 15,16, 15,
11,15,14,212)
Then the variables B will contain the following information:
BOO =P
B(2) =011 (body identifier)
B(3) Julian date of observation
B (4) =71.1.10 (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 10-10
B(10) Electronic calibration delay, seconds x lfll-0
B (1.1) Geometric delay, seconds x 10-10
 lt
B(12) Clock frequency offset from UTC, parts in 10*8
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 (asec or better."
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. Currie (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). Preliminary processing of
the data described here was done at the University of Maryland
and provided by D.G. Currie to the authors 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" COSPAR
Bulletin, No. 6.1 (in press) .
Silverberg, E.C., and Currie, D.G. 197.1 "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: Filtered observations for September 1969 through June 1970 and unfiltered photon detections for July through December 1970

Lunar laser ranging data deposited in the National Space Science Data Center: Filtered observations for September 1969 through June 1970 and unfiltered photon detections for July through December 1970

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