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DESTINATION MOON: A History of the
Lunar Orbiter Program
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- CHAPTER IX: MISSIONS I, II, III:
APOLLO SITE SEARCH AND VERIFICATION
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- The First Launch
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- [228] The launch of
Surveyor I on May 31, 1966, and its need of the Deep Space
Network, together with delivery problems of the photographic
subsystem for the first flight Lunar Orbiter at Eastman Kodak,
caused the tentative July 11 launch date to be slipped to August
9. By August 1 the photo subsystem had arrived and had been
installed on board Lunar Orbiter
I. On August 2 the spacecraft was
transferred to Launch Pad 13 and mated with the Atlas-Agena launch
vehicle. Following the mating, project personnel tested the
compatibility of the spacecraft with the DSIF Station 71 at the
Cape.4
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- On August 9 the Boeing-Lockheed-NASA team
at the Eastern Test Range Launch Complex 13 and at support
facilities near Hangar S counted the spacecraft down to T minus
seven minutes. Then, with the launch only a short time away, an
anomaly in the Atlas Propellent Utilization System caused a
postponement of the mission until the launch window of the
following day.5
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- Lunar Orbiter I, weighing 853 pounds, roared into space atop the
Atlas-Agena D launch vehicle at 19:26 Greenwich Mean Time on
August 10. Launch operations personnel injected the Agena and the
spacecraft into a parking orbit [229] at 19:31 GMT,
and at 20:04 the Agena fired its rocket once more to inject the
Lunar Orbiter into a trajectory toward the
Moon.6 Lunar Orbiter I
deployed its solar panels and
antennas as planned and acquired the Sun (the first celestial
reference for establishing cruise attitude). The mission continued
exactly according to the preflight plan until the time of initial
acquisition of the second celestial reference, the star
Canopus.7
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- The Canopus star tracker sensor proved to
be one of two major problems during the Earth-Moon transit of the
spacecraft. On August 11 at 02:14:57 GMT, flight operations
personnel at the Deep Space Network facilities at JPL commanded
the Canopus sensor to turn on. When it did, it indicated excess
voltage 1.5 times stronger than the preflight calculated signal
voltage. Acquisition of Canopus failed. The reason for the failure
was thought to be excess light reflected from some part of the
spacecraft's structure, stimulating undue response from the
sensitive sensor. This problem should have been detected during
system testing, but it had not been. However, flight operations
attempted a number [230] of tests and
experiments to correct or circumvent the anomaly.
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- The necessity for an attitude-stabilized
spacecraft like Lunar Orbiter to acquire proper stabilization in
reference to the Sun and the star Canopus cannot be overstressed.
Unlike a spin-stabilized spacecraft, Lunar Orbiter I
depended on proper orientation along its yaws pitch, and roll axes
to arrive in the Moon's vicinity in the correct attitude to be
injected into lunar orbit. After the failure of the Canopus sensor
to acquire a fix on Canopus, flight operators were able to save
Lunar Orbiter I's mission by developing an alternate procedure. At
the time of the midcourse maneuver, they commanded the spacecraft
to establish a roll reference by pointing the Canopus sensor at
the Moon.8
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- This maneuver was executed successfully
and after the sensor locked on the Moon, the flight controllers
were reasonably sure that it was operating correctly. They
developed a procedure that used the Canopus sensor during periods
of occultation of the Sun to verify or correct the spacecraft's
orientation.9
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- The other major problem encountered during
the cislunar journey was overheating of the spacecraft. This did
not [231] become serious until after the
midcourse maneuver. To perform this manuever despite the
trouble with the Canopus star tracker, Lunar Orbiter flight
operators used the Moon as the roll reference. The midcourse
maneuver was executed to correct the spacecraft's translunar
trajectory in preparation for deboosting it into orbit around the
Moon. A second manuever was executed to orient the spacecraft
36° off-Sun for a period of 8.5 hours.10 The purpose of this move was to lower the
spacecraft's temperature on the equipment-mounting deck during
transit.
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- The coating on the exterior of the deck
was degrading under solar radiation at the expected rate, and no
acute overheating was experienced until Lunar Orbiter I was
already in orbit around the Moon. Nevertheless, the planned heat
dissipation period when the spacecraft was flown 36° off-Sun
did not seem to retard overall degradation of the thermal coating
on the exterior of the equipment deck.
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- The need to regulate the spacecraft's
temperature and to investigate the Canopus sensor anomaly
necessitated pitch and yaw manuevers every few hours. These added
small accelerations to the spacecraft, all approximately in the
same direction. Their effect on the prediction of the spacecraft's
position at the time of deboost was minimal, and the flight
operators successfully worked around the effects of the
[232]
perturbations resulting from the off-Sun maneuvers. The position
of Lunar Orbiter I at the time of the deboost maneuver into
initial orbit around the Moon was estimated to be less than ten
kilometers off the planned insertion point and presented little
difficulty for flight controllers.11
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- Controllers began a series of commands at
15:22:56 GMT on August 14 to place the spacecraft in orbit. Before
insertion the spacecraft executed another thermal relief maneuver,
which lasted 7.5 hours. The maneuver provided the optimum
temperature conditions before the critical insertion. The final
sequence of commands for insertion was carried out without any
problems, and Lunar Orbiter I was ready to begin the major work of
its mission.12
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- The photographic mission of Lunar Orbiter
I was entirely Apollo-oriented.13 Once the spacecraft had been placed in its initial
orbit, with an apolune of 1,866.8 kilometers and a perilune of
189.1 kilometers, ground control checked out the subsystems. The
necessity to fly off-Sun and the extra number of maneuvers
required because of the Canopus sensor problem had affected the
interrelationships of the spacecraft [233] subsystems, and
flight controllers had to make compensations, especially in the
power system to avoid overtaxing the batteries.
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- On August 15, during the sixth orbit,
ground control successfully commanded Lunar Orbiter I to
read out the Goldstone test film. This film, being the leader on
the supply of film for the mission, had been pre-exposed and
checked out through tests of the readout subsystem at the DSIF
station in Goldstone, California, before the mission. The same
data were now read out again and compared to the known results of
the Goldstone tests in order to check the performance of the
readout and communications subsystems on board the
spacecraft.
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- At the time of the Goldstone test film
readout the thermal problem became acute. The coating on the
exterior of the equipment deck was supposed to radiate excess beat
during periods of solar occultation. It did this approximately as
predicted, but beat levels continued to rises probably because of
more rapid degradation in the pigment Of the coating than had been
expected. However, on August 18, during the twentieth orbit, a
power transistor in the shunt regulator array failed, with a
compensating effect on battery temperatures. The failure placed an
extra load of 1.2 to 1.5 amperes on the power system, increasing
the battery discharge rate during occultation of the Sun. The
extra load meant that the off-Sun angle of 36° could
[234]
be reduced slightly at the time when sufficient power for readout
was required of the power system.14 The analysis and compensatory action for this
problem reflected outstanding flight operations.
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- After orbiting the Moon for four days and
twenty-three hours Lunar Orbiter
I began the first operation of its
photo subsystem since the readout of the Goldstone test film.
Eleven frames were advanced and processed during the twenty-fifth
orbit at 12:12:13 GMT on August 18, bringing the unexposed film
into position for the first photographic sequence, which was to
begin on orbit 26.
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- The photographic subsystem, which Eastman
Kodak had designed and built, was put together with the precision
of a Swiss watch. Every component of the subsystem was tightly
housed in an aluminum "bath tub" a little larger than a large
round watermelon. A precision instrument with a very complex task
to perform, the photo subsystem operated like a thrashing machine.
The film, which had to go through three plane changes, was drawn
from the supply spool, clamped in a movable platten, moved and
exposed simultaneously, and advanced farther to make room for a
new film-all in a matter of a few seconds.15
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- [235] The first site
to be photographed, Site I-O (a portion of Mare Smythii),
was covered by the Orbiter's dual lens camera as planned. Photo
subsystem telemetry to Earth appeared to be normal. The photos
were taken as follows. Ground control commanded the spacecraft to
open the camera thermal door. Two photo sequences were then
executed: one of sixteen frames in the high-resolution mode and
one of four frames in the medium-resolution mode. They were made
at an altitude of 246 kilometers above the Moon while the
spacecraft's velocity relative to the lunar surface was 6,400
kilometers an hour. Exposure time for each shutter was 1/50 of a
second, and simultaneous medium- and high-resolution pictures were
made every ten seconds. After the sequences, the thermal door was
closed and the film was processed.16
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- Five hours later the readout process
began, at 19:50:52 GMT on August 18. All the medium-resolution
frames were of excellent quality, but reconstruction of four
high-resolution frames revealed severe image
smearing. The first high-resolution frame contained some
unsmeared data, but George Hage, the Boeing Lunar Orbiter Program
Engineer, recognized it to be a double exposure. The first
exposure [236] of the frame contained unsmeared data and proved
to have been taken prematurely of a feature east of the planned
target area when the V/H sensor was turned on.17 Apparently the shutter of the 610 mm lens was out
of synchronization with the V/H sensor; further investigation
demonstrated that this supposition was true.18
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- Flight operators in charge of mission
photography set up an experiment to examine the possible causes of
the smearing. After completion of the Site I-O photography ten
more exposures were made with the 610 mm lens for purposes of
evaluating exposure 26, the first picture of the four-frame
sequence after photographing. Site I-O. One test involved the use
of different exposure rates with and without the V/H sensor turned
on. A second test was used to determine if, in fact, the V/H
sensor was causing abnormal shutter operations. It consisted of
three steps:
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- 1) The camera thermal door was opened and
the V/H sensor was turned on.
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- 2) The sensor was left on for
approximately 2 minutes and then turned off.
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- 3) The camera thermal door was then closed
and the camera shutter was commanded to take a picture with the
door closed and to move fresh film into the camera for the next
photograph.19
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- [237] The second test
confirmed that the abnormal operation occurred when the V/H sensor
was on; a high-resolution exposure was made with the thermal door
open and no shutter command, but no medium-resolution picture was
taken when the shutter command was given. Despite the problem,
flight controllers made no deviations from the flight plan, and
the spacecraft was transferred to its lower, final orbit at
09:49:58 GMT on August 21.20 The new orbital parameters were: apolune, 1,855
kilometers; perilune, 58 kilometers; inclination to the lunar
equator, 12-32°.21
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- Just before the orbit transfer,
Lunar Orbiter I took two frames of medium- and high-resolution
pictures of the Moon's far side at an altitude of l,497
kilometers. The V/H sensor was off, because there was no need for
image-motion compensation at such a high altitude. After the
frames were read out, they revealed high-quality pictures of the
lunar surface in both medium- and high-resolution modes, without
smearing.22
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- Another problem occurred before the final
orbit transfer, requiring the photo subsystem to take additional
unplanned photographs. The Bimat apparently was sticking.
[238]
The original plan had called for fresh Bimat to be placed on the
processing drum at least every 15 hours. This meant that two
frames would be processed every four orbits. However, evidence of
Bimat stick in the early frames precipitated the decision to use
additional film which would permit processing during every orbit.
Eight extra pictures were to be taken.23 This change and the extra diagnostic pictures taken
to evaluate the high-resolution shutter problem forced a revision
in the planned photographic coverage of the remaining sites. The
result was that only eight exposures would be taken of Sites 4, 6,
and 8 while the 24 other sites would receive the original 16-frame
coverage.24
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- The trouble in the high-resolution camera
lens shutter continued to plague photography when the V/H sensor
was operating, despite the increase in output voltage which
Eastman Kodak technicians bad recommended during analysis of the
problem. Further analysis revealed that the logic-control
circuitry of the 610-mm-lens focal-plane shutter was susceptible
to electromagnetic interferences which caused it to trip at the
wrong part of the image-motion compensation cycle. It was not
possible to solve this problem by modifying procedures, and
low-altitude high-resolution [239] photography on
the first mission proved a failure despite further attempts to
correct the problem.
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- Nitrogen gas, used by the attitude control
subsystem to manuever the spacecraft, had been expended in greater
amounts than originally planned because of the difficulties in the
Canopus star tracker and alterations of planned photography caused
by the shutter problems and the evidence of Bimat sticking.
Moreover, thermal relief maneuvers and excess attitude update
maneuvers, together with the failure of a gas regulator, increased
the rate of nitrogen usage. Between August 23 and 31 an average of
0.17 kilograms of nitrogen was expended per day. Flight
controllers tried an economizing procedure. They commanded the
spacecraft to fly off-Sun on its pitch axis and to update its
attitude on the pitch and yaw axes using the coarse Sun sensors
and on its roll axis using the Canopus sensor. This change
resulted in an expenditure of 0.04 kilograms per day between
September 1 and 14.25
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- From the final orbit perilune of 58
kilometer, Lunar Orbiter
I was deboosted successfully to a
lower altitude of 40.5 kilometers for further photography on
August 25. This move was the result of an analysis of the V/H
sensor in a duplicate Lunar Orbiter photo subsystem on the ground
[240]
by Eastman Kodak engineers on August 24. They had concluded that
there was a possibility that the camera would operate normally
below an altitude of 51 kilometers.26 They reasoned that, since the ratio of velocity to
height would be higher in the new, lower orbit, the image-motion
compensation mechanism might be forced into synchronization with
the 610 mm lens's focal-plane shutter. Synchronization was,
unfortunately, never attained, but there was some reduction in
smearing because a higher solar lighting angle permitted a change
in shutter speed from 1/50 to 1/100 second.27
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- By August 29 Lunar Orbiter I had completed
its photographic acquisition, with a total of 205 exposed frames.
Of these, 38 frames had been taken in the initial orbit; 167 were
made in the lower orbits. The spacecraft photographed all nine
potential Apollo landing sites. Pictures of eleven sites on the
far side of the Moon and two Earth-Moon pictures were also taken.
The complete readout of the 28 photographs began on August
30.28
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- Despite the malfunctions in the
photographic subsystem the spacecraft succeeded in taking many
historic pictures. Command and maneuver requirements were
developed to take, [241] in near
real-time, such pictures as those of the morning and evening
terminator on the lunar surface, the Earth as seen from the Moon's
vicinity, numerous farside pictures, and additional photographs of
sites of interest on the near side. Lunar Orbiter I
photographed such areas as potential targets for Mission B, major
craters, and mare and upland areas useful as Apollo navigation
landmarks and was mostly able to satisfy the requirements to take
these photographs.29
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- Of all the pictures which Lunar Orbiter I made,
one of the most spectacular was the first photograph of the Earth
taken from the vicinity of the Moon. This picture was not included
in the original mission plan, and it required that the
spacecraft's attitude in relation to the lunar surface be changed
so that the camera's lenses were pointing away from the Moon. Such
maneuvering meant a calculated risk and, coming early in the
flight, the unplanned photograph of Earth raised some doubts among
Boeing management about the safety of the spacecraft.
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- Robert J. Helberg, Boeing's Program
Manager for Lunar Orbiter, opposed such a hazardous unnecessary
risk. The spacecraft would be pointed away from the Moon so that
[242]
the camera's lenses could catch a quick view of Earth tangential
to the lunar surface. Then, once the pictures were made (flight
controllers would execute two photo sequences on two different
orbits), Lunar Orbiter
I would disappear behind the Moon
where it would not be in communication with ground control. If,
for some reason ground control failed to reestablish
communications with it, the Apollo-oriented mission photography
would probably remain undone, Moreover, Boeing had an incentive
riding on the performance of the spacecraft, and Heiberg did not
think it prudent to commit the spacecraft to a series of maneuvers
for which no plans had been made.30
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- The understandably conservative Boeing
stance was changed through a series of meetings between top NASA
program officials, including Dr. Floyd L. Thompson, Clifford H.
Nelson, and Lee R. Scherer. They convinced Heiberg that the
picture was worth the risk and that NASA would make compensation
in the event of an unexpected mishap with the spacecraft. After
agreement had been reached, Lunar Orbiter flight controllers
executed the necessary maneuvers to point the spacecraft's camera
away from the lunar surface, and on two different orbits (16 and
26) it recorded two unprecedented, very useful photographs.
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- [243] The Earth-Moon
pictures proved valuable for their oblique perspective of the
lunar surface. Until these two photographs, all pictures had been
taken along axes perpendicular or nearly perpendicular to the
Moon's surface. On subsequent Lunar Orbiter missions oblique
photography was planned and used more often.31
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- Lunar Orbiter I began its extended mission on September 16 after
completion of photographic readout. During this period
non-photographic data was telemetered to Earth at regular, planned
intervals. Flight controllers monitored the orbital behavior of
the spacecraft, the micrometeroid detectors, and the condition of
the power, attitude control, and communications subsystems.
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- By October 28 the condition of
Lunar Orbiter I had deteriorated significantly. Scherer issued a
status report which pointed out the following: 1) very little gas
remained for attitude control (0.4 kilograms at 7 kilograms per
square centimeter-100 psi.-pressure); 2) estimated stabilized life
of spacecraft was two to five weeks; 3) the battery was losing
power because of prolonged overheating, and if it fell below 15
volts, the onboard flight programmer would lose essential
[244]
parts of its memory, 4) the transponder was responding
erractically, and the inertial reference unit was losing its
ability to keep the spacecraft stable. The program manager and his
staff realized that loss of control over communication
transmission from Orbiter
I could jeopardize the mission of
the second Lunar Orbiter. They conferred with members of the
Langley Lunar Orbiter Project Office who, in turn, decided to
command the spacecraft to impact on the far side of the Moon
during its 577th orbit on October 29. This maneuver, successfully
executed, brought the first mission to an end.32
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