5.0 INFLIGHT SCIENCE AND PHOTOGRAPHY
The inflight experiments and photographic tasks conducted during the
Apollo 15 mission are discussed in this section. The discussion is concerned
primarily with experiment hardware performance and data acquisition
operations. In instances where preliminary scientific findings were available
at the time of report preparation, they are included, but more complete
information on scientific results will be found in reference 2.
The experiments located in the scientific instrument module bay of the
consisted of a gamma ray spectrometer, an X-ray
spectrometer, an alpha-particle spectrometer, a mass spectrometer; and a
subsatellite which is the vehicle for a particle shadows/boundary layer
experiment, an S-band transponder experiment, and a magnetometer
experiment. The subsatellite
was launched successfully just
prior to transearth injection on August 4 at approximately 2100 G.m.t., and
was inserted into a 76.3-by-55.1-mile lunar orbit with an inclination of
minus 28.7 degrees. The three subsatellite experiments are expected to
acquire data for a period exceeding 1 year. At the time of launch, the moon
was in the magnetosheath (transition) region of the earth's magnetosphere
one of several data collecting regions of scientific interest.
All subsatellite experiments are turned off while the battery is being
recharged after each tracking revolution. Both the magnetometer and
particle shadows/boundary layer experiments are acquiring data on all
revolutions except those when the battery is being charged.
Other inflight experiments consisted of ultraviolet photography of
the earth and moon, photography of the Gegenschein from lunar orbit, an
S-band transponder experiment using the command and service module and
lunar module S-band communication systems, a down-link bistatic radar
experiment using both the S-band and VHF communications systems of the
command and service module and an Apollo window meteroid experiment.
Photographic tasks that were designated as detailed objectives rather
than experiments are also discussed. They are the service module orbital
photography employing the panoramic camera, the mapping camera, and the
laser altimeter; and command module photography of lunar surface areas and
astronomical subjects. A brief description of the equipment used for these
experiments and photographic tasks is given in appendix A.
5.1 GAMMA-RAY SPECTROMETER EXPERIMENT
The gamma-ray spectrometer was operated in lunar orbit for over 90 hours.
The instrument was operated in the minimum-background mode for prime data
collection approximately 65 percent of the time.
The remaining of the time it was operated in various non-minimum-background modes
to determine the effects of background radiation sources on the prime data.
The instrument was also operated for approximately 50 hours during
transearth flight obtaining background data necessary for analysis of the
lunar data, and to acquire data from galactic sources.
The instrument as well as the deployment boom performed well throughout
the mission. However, two anomalous conditions occurred which affected
instrument calibration. First, a downward drift in the linear gain of the
photomultiplier or pulse analyzer was detected after the first boom extension
(prior to undocking in lunar orbit) when several lines in the spectrum of the
Apollo lunar surface experiment package fuel capsule were used for
calibrations. The drift decreased in magnitude from an initial rate of 1
percent per hour to 0.4 percent per day and, eventually, reached a fairly
stable state. The second anomalous condition was noted about 2-3/4 hours
after transearth injection, when spectrum zero shifted eight channels,
causing loss of the 0.279-million-electron-volt calibration reference.
Commencing at 246:56, the problem disappeared for approximately 25
hours, returning at 271:47 and remaining for the rest of transearth flight.
These problems are discussed further in section 14.3.4.
The preliminary data indicates variations in radioactivity as the
spacecraft passed over different kinds of terrain. The western mare areas
are generally the highest in radioactivity, with the eastern maria being
somewhat lower. The highlands are the lowest in activity with a slightly
lower level in the far-side highlands. The data further indicate a continuum
level comparable to that predicted from Ranger 3 and Luna 10 data. Peaks
due to potassium, thorium, oxygen, silicon, and iron have been identified.
Detailed analysis is expected to show the presence and distribution of
uranium, magnesium, aluminum, and titanium.
5.2 X-RAY FLUORESCENCE EXPERIMENT
All X-ray spectrometer objectives were achieved and no hardware
problems were noted. About 90 hours of data were obtained from operation of
the instrument in lunar orbit, and approximately 26 hours of data were
acquired while in transearth flight. During this latter period, the
instrument was pointed at six preselected locations to acquire data on
possible variations in X-ray intensity. Two observations were coordinated
with simultaneous ground-based observations. After 276 hours, the
instrument was left on to obtain data for use in the search for new sources
of X-ray emission and to improve spectral information on known sources.
Near the end of transearth flight, an engineering test was conducted
to determine if the gas-filled proportional counters Would be damaged by
direct impingement of solar X-rays. The experiment continued to operate
satisfactorily after the test.
The preliminary data shows that the fluorescent X-ray flux was more
intense than predicted; that the concentration of aluminum in the highlands
is about 50 percent greater than in the maria; and that the ratio of
magnesium-to-aluminum in Mare Smithii and Mare Chrisium is about 50 percent
greater than in the highlands between, and to the east and west of, the two
maria. Analysis of the X-ray astronomy observations made enroute to the earth
has shown that the intensity in X-ray output of Scorpius X-1 and Cygnus X-1
fluctuates with periods of several minutes.
5.3 ALPHA-PARTICLE SPECTROMETER EXPERIMENT
All primary objectives of the alpha-particle experiment were achieved.
The spectrometer was operated for approximately 80 hours in lunar orbit to
acquire prime data, and approximately 50 hours during transearth coast to
acquire background data.
Two of the ten detectors were intermittently noisy. The noise was at a
very low rate (approximately 0.5 count per second) with occasional bursts at
higher rates. Since the noise was generally restricted to one detector at a
time, the loss of data is not expected to have a significant effect on the
validity of the analysis.
An engineering test was performed near the end of transearth flight
(in conjunction with the test on the X-ray spectrometer). The open
experiment covers, which permitted direct sunlight impingement on the
instrument, resulted in three of the ten detectors (including the two noisy
detectors) showing some evidence of photosensitivity.
The planned coverage of the lunar surface was obtained. The alpha
particle spectrometer did not detect any local areas of radon enhancement (An objective
of the experiment was to locate craters or fissures
by detecting alpha particles emitted by radon isotopes - daughter products
of uranium and thorium).
The general radon evolution rate of the moon is three orders of magnitude
less than that of earth. A refinement of the data, in which summation of
counts from successive orbital passes over the same area is made, will be
required to make more definitive statements about the lunar distribution of
5.4 MASS SPECTROMETER EXPERIMENT
Thirty-three hours of prime lunar orbit data were collected with the
command and service module minus X axis in the direction of travel, and 7
hours of background data with the command and service module pointed in the
opposite direction. During transearth coast, approximately 48
hours of data were gathered, including waste water dumps, oxygen purges, and boom-
The mass spectrometer boom retract mechanism in the scientific
instrument module stalled during five of twelve cycles. Data, supported by
the Command Module Pilot's observations during extravehicular activity,
confirmed that the boom had retracted to within 1 inch of full retraction.
Each of the five cycles in which the boom did not fully retract was preceded
by a period of cold soaking of the boom. In each instance, the boom would
retract fully after warm-up. The boom was fully retracted for command
module/service module separation. This anomaly is discussed further in
The instrument operated well, providing good data. Even though the
boom retraction problem resulted in failure to collect prime data during
one scheduled period, and real-time scheduling problems prevented
instrument operation for another scheduled period, an adequate amount of
data was acquired.
The mass spectrometer measured an unexpectedly large amount of gas at
orbital altitude around the moon. This amount was an order of magnitude
greater than that seen during transearth coast. Many gases were detected,
including water vapor, carbon dioxide, and a variety of hydrocarbons. Data
obtained during transearth coast indicate that a gaseous contamination cloud
existed up to a distance of 4 feet from the command and service module, but
contamination was not detected at the maximum extension of the mass
spectrometer (24 feet).
5.5 PARTICLE SHADOWS /BOUNDARY LAYER EXPERIMENT
The charged-particle telescope detectors were turned on immediately
after subsatellite launch and are operating normally. Proper operation of
the proton detection system was indicated when a large flux of protons in
the 35 000- to 100 000-electron-volt range were observed near the
magnetopause (fig. 5-3). Twenty-four hours after subsatellite launch, the
electrostatic analyzer detectors were turned on, and have operated normally
with no evidence of high-voltage corona or arcing.
When the moon is not in the earth's geomagnetic tail, the effect of
the moon's shadow on the solar wind electrons is clearly detected. The
variation in the shadow shape is rather large. With the moon in the earth's
tail, a very tenuous plasma is seen. Within the plasma sheet, intensities
increase with some flow of plasma from the earth's direction.
5.6 SUBSATELLITE MAGNETOMETER EXPERIMENT
The magnetometer was turned on when telemetry from the subsatellite
was acquired, and the instrument has performed satisfactorily. The
experiment has operated continuously except for an 18-hour period after the
lunar eclipse of August 6, and periods when the power is turned off to
enable the batteries to return to full charge.
The magnetometer is returning better-than-expected information in
relation to detecting surface anomalies. The principal investigator is
carrying out hand calculations on far-side data that indicate excellent
repetitive information over the craters Gagarin, Korolev, and Van de
Graaff. While in the solar wind, the magnetometer is mapping the signature
of the diamagnetic cavity behind the moon. As the subsatellite crosses the
terminator, variations in the solar magnetic field by factors of two to
three are detected by the magnetometer. These may be caused by interaction
of the solar wind with local magnetic regions near the limb. More careful
long-term analysis is required to confirm this preliminary finding.
5.7 S-BAND TRANSPONDER EXPERIMENT
5.7.1 Command and Service Module/Lunar Module
Good gravitational profile data along the spacecraft lunar ground
tracks were obtained. The anticipated degradation of the data caused by
changes in spacecraft position from uncoupled attitude control engine firings
was not significant. Indications are that the gross shapes of mascons in
Serenitatis, Crisium, and Smythii can be established. This complements the
Apollo 14 results on Nectaris. Detailed gravity profiles of the Apennines and
Procellarum regions were also obtained.
The initial data contained a high level of noise caused by a wobble
about the spin axis. The wobble was inherent in the subsatellite deployment
and was subsequently removed by the onboard wobble damper.
The subsatellite S-band transponder is working well, and is being
operated every twelfth lunar revolution. The tracking data shows that the
perilune variation is following preflight predictions and is expected to
confirm the predicted orbital lifetime (greater than 1 year). The
subsatellite transponder has shown at least one new mascon in the region of
the crater Humboldt on the eastern lunar near side. Repeated overflights of
the lunar near side from varying altitudes as the subsatellite orbit decays
will be necessary before an accurate gravitational map can be made and large
5.8 DOWN-LINK BISTATIC RADAR OBSERVATIONS OF THE MOON
The experiment data consists of records of both frequencies (S-band
and VHF) during the front-side passes on lunar revolutions 17 and 28.
During these dual-frequency periods, signals were bounced off the moon and
received at Goldstone (210-ft dish antenna for S-band) and at Stanford
University (150-ft dish antenna for VHF). On revolutions 53 through 57 (the
crew sleep period), only the VHF frequency was reflected from the moon to
The experiment results will require considerable data processing.
Determination of the bulk dielectric constant and near-surface roughness
along the spacecraft track appears possible with the present data. S-band
data from revolution 17 are not usable because of incorrect spacecraft
attitude. However, VHF data from revolution 17 appear to be of high quality.
The attitude error was discovered and corrected in time for revolution 28,
and all the data for that revolution are of excellent quality. The VHF
experiment conducted during revolutions 53 through 57 provided high quality
data. Apollo 15 data may be correlated with data obtained from the Apollo 14
bistatic radar experiment since the spacecraft groundtracks of
Apollo 15 during both S-band/VHF operation and VHF-only operation intersect the
Apollo 14 groundtrack during S-band/VHF operation.
5.9 APOLLO WINDOW METEOROID EXPERIMENT
The command module side and hatch windows were scanned at a
magnification of 20X prior to flight to determine the general background of
chips, scratches and other defects. Postflight, the windows will again be
scanned at 20X (and higher magnifications for areas of interest) to map all
visible defects. Possible meteoroid craters will be identified to determine
the meteoroid cratering flux of particles responsible for the degradation of
glass surfaces exposed to the space environment.
5.10 ULTRAVIOLET PHOTOGRAPHY - EARTH AND MOON
Ultraviolet photographs were obtained while in earth and lunar orbit,
and during translunar and transearth coast. The following table lists the
ultraviolet photography sequences performed on Apollo 15. Each sequence
consisted of two exposures without the use of a filter and two exposures
each with a 2600-angstrom filter, a 3750-angstrom filter, and a 4000- to 6000-
angstrom visual-range filter. In addition, some color-film exposures were
obtained, as planned, with the visual-range filter. These are noted in the
last column of table 5-1. Preliminary examination shows that the exposures
Table 5-I.- ULTRAVILOT PHOTOGRAPHY
5-11 GEGENSCHEIN FROM LUNAR ORBIT
Photography of the Gegenschein and Moulton Point regions from lunar
orbit was performed twice, as planned, during revolutions 46 and 60, and
at least six exposures were obtained during each sequence. However, the
photographs are unusable because incorrect signs were used in premission
calculations of spacecraft attitudes. Ground-based photography in support
of the inflight photography was performed during the mission at the Haleakala
Observatory, Maui, Hawaii, and after the mission at the McDonald Observatory,
Fort Davis, Texas.
The camera system used for the Gegenschein experiment and other astronomy tasks
performed well. A comparison of preflight and postflight
calibration exposures with the faintest brightness observed in the Apollo
15 exposures (of the Milky Way) demonstrates that this camera system is
very satisfactory for the Gegenschein experiment, now scheduled for the
Apollo 16 mission.
5.12 SERVICE MODULE ORBITAL PHOTOGRAPHY
5.12.1 Panoramic Camera
The panoramic camera was carried on Apollo 15 to obtain high-resolution
panoramic photographs of the lunar surface. The areas photographed included
the Hadley Rille landing sites (fig. 4-1 and 4-2), several areas being considered
as the Apollo 17 landing site, the Apollo 15 lunar module ascent stage impact
point, near-terminator areas, and other areas of general coverage. Anomalous
operation of the velocity/altitude sensor (section 14.3.1) was indicated on the
first panoramic camera pass on revolution 4 and subsequent passes; however,
good photography was obtained over all critical areas.
The delay in lunar module jettison caused cancellation of photographic passes
planned for revolutions 58 and 59. These passes were rescheduled for revolutions
60 and 63, but sidelap with adjacent areas photographed on revolutions 33 and 38
All imagery is of very high quality. Examination of the film shows that less than one
percent of the total film exposed was seriously degraded by the velocity/altitude sensor
5.12.2 Mapping Camera
The mapping camera was carried aboard the Apollo 15 service module to
obtain high-quality metric photographs of the lunar surface. Mapping camera
operation was desired during all panoramic camera passes and on selected
dark-side passes to assist in analysis of data from the laser altimeter. The
camera functioned normally and, essentially, the entire area overflown in
daylight was photographed. However, the laser altimeter failed (see the
following section) and all scheduled dark-side mapping activities subsequent
to revolution 38 were deleted. A problem with the mapping camera deployment
mechanism was also experienced. The camera extension and retraction cycles
varied from 2 to 4 minutes as compared to about 1 1/2 minutes required prior
to flight. After the last deployment, the camera did not completely retract.
This anomaly is discussed further in section 14.3.3.
The mapping camera was turned off during the panoramic camera pass
over the landing site on revolution 50 in a test to determine if the
velocity/altitude sensor anomaly might be related to the mapping camera
operation. This resulted in a minor loss of coverage. Also, the
photographic pass planned for revolution 58 was deferred until revolution
60 because of the delay in lunar module jettison. The consequence of this
was a decrease in sidelap below the desired 55 percent.
Approximately 6 hours of mapping camera operating time remained at
transearth injection. About 1 1/2 hours of this were expended
photographing the receding moon, and 3 1/2 hours were used photographing
selected star fields with the stellar camera associated with the mapping
Image quality is excellent throughout the entire sequence of 3400
frames. The entire portion of the lunar surface which was overflown by
Apollo 15 in daylight has been covered by excellent stereoscopic photography
which is as well suited to detailed analysis and geologic interpretation as
it is to mapping.
5.12.3 Laser Altimeter
The laser altimeter was flown to accurately measure lunar topographic
elevations in support of mapping and panoramic camera photography, and
inflight experiments. The altimeter was designed to supply a synchronized
altitude measurement for each mapping camera exposure on light-side
photography, and independent altitude measurements on the dark side to
permit correlation of topographic profiles with gravity anomalies obtained
from spacecraft tracking data.
Operation of the altimeter was nominal through revolution 24, but improper
operation was noted on the next operation (revolution 27). The performance of
the altimeter became progressively worse until, on revolution 38, the altimeter
ceased to operate (sec. 14.3.2). Consequently, the altimeter was not operated
on subsequent dark-side passes, although operation on lightside mapping camera
passes was continued. On revolution 63, an attempt was made to revive the
altimeter through a switching operation by the Command Module Pilot, but the
effort was not successful.
Approximately 50 percent of the planned altimeter telemetry data were
actually obtained before the instrument failed. The data from the early
orbits have been correlated with S-band transponder data for the frontside
pass, and show the shape of the gravity anomalies as related to mare basins.
The complete circumlunar laser altimeter data show that, relative to the
mean lunar radius, the average lunar far side is about 2 kilometers (1.1
mile) high and the average near side is about 2 kilometers low.
5.13 COMMAND MODULE PHOTOGRAPHY
While in lunar orbit, photographs were taken from the command module
of lunar surface sites of scientific interest, and of specific portions of
the lunar surface in earthshine and near the terminator. Also, while in
lunar orbit, photographs were taken of low-light-level astronomical
subjects including the solar corona, the zodiacal light, lunar libration
point L4, and of the moon as it entered and exited the earth's umbra during
lunar eclipse. During translunar and transearth coast, photographs were
taken of a contamination test and star fields were photographed through the
command module sextant.
In accomplishing some of the tasks, the crewman obtained extra frames
and some with longer exposures than required. This will enhance the value
of the total data desired. The only 16-mm data acquisition camera magazine
containing very-high-speed black-and-white film was lost. About 35 percent of
the magazine had been exposed during lunar orbital flight and transearth
coast for solar corona and sextant star field photography. The most
probable cause of the loss of the magazine was that it floated through the
hatch during the Command Module Pilot's extravehicular activity. This
required a substitution of a slower black-and-white film magazine for the
final sextant star field photography and real-time update for contamination
photography but, because premission-planned exposure settings were used
with the much slower film, the sextant star field photographs are not
Photographs were obtained of 21 of 23 specific lunar surface targets,
the solar corona, the moon during lunar eclipse as it entered and exited the
earth's umbra, star fields through the command module sextant, lunar
libration region L4, and specific areas of the lunar surface in earthshine
and in low light levels near the terminator. Near-terminator strip
photography scheduled on revolution 58, and 2 of the 23 lunar surface
targets scheduled on revolutions 58 and 59 were deleted because of the
delay in lunar module jettison due to problems during tunnel venting
operations and subsequent extension of the crew's sleep period. Based on
preliminary examination of the dim-light photography, it appears that
excellent quality imagery was obtained of the solar corona, the zodiacal
light and the lunar surface in earthshine.
5.14 VISUAL OBSERVATIONS FROM LUNAR ORBIT
Visual observations from lunar orbit was an objective implemented for
the first time on this mission. The Command module Pilot was asked to make
and record observations of special lunar surface areas. Emphasis was to be
placed on characteristics difficult to record on film, but which could be
delineated by the eye, such as subtle color differences between surface
units. All of the scheduled targets were observed and the results relayed.
These results are documented in reference 2. Significant observations were
a. Fields of cinder cones were discovered on the southeast rim of
Mare Serenitatis (Littrow area) and the southwest rim of the same mare
basin (Sulpicius; Gallos area).
b. A landslide or rock glacier was delineated on the northwest rim
of the crater Tsiolkovsky on the lunar farside (fig. 4-5).
c. A ray-excluded zone around the crater Proclus on the west rim of
Mare Crisium was interpreted as being caused by the presence of a fault
system at the west rim of the crater.
d. Layers on the interior walls of several craters were found and
were interpreted as volcanic collapse craters, or "caldera", in the maria.