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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 Third Orbiter
Mission
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- [259] The third
mission differed slightly from the first two because it
concentrated its photography on Apollo and Surveyor site
confirmation instead of site search. To permit confirmation
photography of sites both north and south of the lunar equator the
spacecraft's orbital inclination was increased to 21°. The
convergent stereo photography of Mission II had proved successful
and potentially useful to the Apollo and Surveyor programs. It
consisted of making two "footprints" of the same area on two
successive orbits. To accomplish this at the higher orbital
inclination, the camera would necessarily be tilted during one of
the two sequences. Resolution of a convergent stereo picture pair
was slightly degraded because of the camera tilt, and a loss of
one-meter to two-and-one-half-meter, or perhaps three-meter,
resolution resulted.55
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- The Air Force Aeronautical Chart and
Information Center (ACIC) and the Army Map Service bad evaluated
the Mission II convergent stereo photography and had concluded
that "this type of photography increases the topographic knowledge
that can be obtained concerning potential landing
sites."56 [260] The Lunar Orbiter Project Office at Langley
planned to include more convergent stereo coverage on Mission III
as a result of the ACIC and Army Map Service (since January 1970,
U.S. Army TOPOCOM) evaluations.
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- On November 15, 1966,a technical
interchange meeting convened at the Jet Propulsion Laboratory to
assess the various methods of calibrating the Lunar Orbiter's 610
mm high-resolution camera for the new photographic tasks. Precise
geometric calibration was mandatory if stereo photography was to
be conducted successfully on the three remaining missions. The
calibration was to be done at the photographic subsystem level,
and the members of the meeting determined the method to
use.57 Leon J. Kosofsky coordinated the calibration
activities.
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- Although primarily a reconnaissance
photographic system, rather than a mapping system, the Lunar
Orbiter photo subsystem was upgraded after Mission I. The
Aeronautical Chart and Information Center and the Army Map Service
had previously argued that the use of reseau marks on the camera
film or a grid on the camera lens would greatly facilitate the
utilization of photographic data for purposes of lunar mapping.
Langley accepted the idea of pre-exposing reseau marks on the
camera film for Mission II and all subsequent [261] missions.
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- On January 5 the photo subsystem for
Spacecraft 6 (the third flight spacecraft) was installed, and
Boeing conducted the functional check-out with the Deep Space
Instrumentation Facility. The spacecraft's inertial reference unit
(IRU) was taken out, tested, and reinstalled and the actuator for
solar panel 3 was replaced. Retesting at Hangar S was accomplished
by January 13 in preparation for mating with the launch
vehicle.58
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- Meanwhile, on January 5 the Ad Hoc
Surveyor/Orbiter Utilization Committee of OSSA bad approved the
plan for the third Lunar Orbiter mission:
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- Mission III is primarily designed to
photograph promising areas that have been identified by screening
Lunar Orbiter I and II photographs and for which additional data
is needed to confirm their adequacy as Apollo and/or Surveyor
landing sites. In addition Mission III will provide photography of
broad scientific interest as did Missions I and
II.59
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- The mission would also obtain precision
trajectory information to be used in improving the definition of
the lunar gravitational field and measurements of micrometeoroid
flux and of radiation dosage levels in near-lunar environment for
use in evaluating the spacecraft's performance. [262] Finally
Lunar Orbiter III would serve as a target for the Manned Space Flight
Tracking Network and the Orbit Determination
Program.60
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- The Launch Readiness Review for
Lunar Orbiter III and for the back-up (Spacecraft 7) was held at the
Eastern Test Range facilities on January 17. Both Orbiters were
found to be ready for launch, and personnel working with
Spacecraft 6 proceeded with the preparations for that event. The
tentative date for launch was February 3.61
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- Boeing and Eastman Kodak were attempting
to resolve the problems which had caused minor film processing
defects on the first two Missions. Manufacturing irregularities
and bubbles in the Bimat bad been the chief causes of these
defects. As it turned out, localized Bimat processing defects
continued to appear on some photographs from all five missions,
despite attempts to correct the condition. Still unresolved as the
third launch approached was the failure of the TWTA aboard Lunar
Orbiter II. However, Boeing engineers were modifying this
component so that excess heat build-up could be removed during the
flight, thus prolonging the tube's lifetime. Readout times would
also be reduced in the event of a heat build-up, and flight
controllers would [263] monitor the flow
of electrical current through the traveling wave-tube amplifier,
since program scientists considered any irregularities in the flow
to be an indication of pending trouble in it.62
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- Lunar Orbiter III lifted off of Pad 13 at the Eastern Test Range at
01:17 Greenwich Mean Time on February 5, 1967. (The February 3
launch window had been canceled because of problems encountered in
the ground power-supply system at Launch Complex 13.) Despite
numerous pre-launch problems the liftoff was successfully
accomplished on a flight azimuth of 80.8° at the start of the
February 5 launch window. Ground control placed the
Agena-spacecraft combination in a parking orbit for approximately
ten minutes before injecting it into a cislunar
trajectory.63
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- Following injection the spacecraft
separated from the Agena, deployed its solar panels and antennas,
and acquired the Sun as an attitude reference. Seven hours into
the mission flight controllers commanded Lunar Orbiter III to
turn on its Canopus star tracker and give a star map before
Canopus acquisition. It executed this command successfully. On
Monday, February 6, at 37 hours into the mission [264] the Space Flight
Operations Facility tracking Lunar
Orbiter III commanded a midcourse
correction maneuver to adjust the spacecraft's cislunar trajectory
in order to hit the preplanned aiming point for deboost into lunar
orbit, As on previous missions, the midcourse maneuver was so
accurate that no second maneuver was required.64
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- At 4:54.p.m. Eastern Standard Time on
February 8 Lunar Orbiter
III fired its 100-pound-thrust
rocket engine for 9 minutes, 2.5 seconds to decelerate the
spacecraft into its initial orbit. The parameters were: apolune,
1,801.9 kilometers; perilune, 210.2 kilometers; inclination,
20.93°; period of orbit, 3 hours 25
minutes.65 Ground control tracked the spacecraft in the
initial orbit for approximately four days (25 orbits) to obtain
data for analysis of the lunar gravitational effect. Following
this the spacecraft was transferred to a new orbit with a low
perilune of 55 kilometers and an apolune of 1,847
kilometers.66 Inclination to the lunar equator was
20.9°.67
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- As Lunar
Orbiter III had executed its
deboost maneuver Lunar Orbiter
II was still in orbit around the
Moon. On February 6 ground control began tracking both spacecraft
[265]
simultaneously, thus demonstrating its ability to track two
spacecraft in different orbits around the Moon at the same time.
This exercise greatly extended the usefulness of each mission by
providing simultaneous telemetry on the two orbiting spacecraft.
Monitoring showed that all Lunar
Orbiter II subsystems were
operating normally.68
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- Lunar Orbiter III began its photographic mission on February 15 over
primary Site III P-1 at 35°15" east longitude, 2°5"
north latitude, near the crater Maskelyne F in the southeastern
region of Mare Tranquillitatis. The first readout in the primary
mode revealed photographs of excellent quality. A solar flare
occurred at 12:54 p.m. EST on February 13. Though it had a high
amount of optical activity, there was little of the proton
activity that could have presented a danger to the film on board
the spacecraft.69 The first readout revealed no fogging of the film
and indicated that all subsystems were working normally.
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- The film advance mechanism in the readout
section of the photo subsystem of Lunar Orbiter III
began to show erratic behavior even during the mission's
photographic phase. Because of this, program officials decided to
begin final readout earlier than planned. Ground control at the
[266]
DSN decided not to photograph secondary Site S-32, an oblique shot
of the Grimaldi crater area. A total of 211 out of 212 planned
frames had been exposed when, at 1:36 a.m. EST on February 23,
flight controllers commanded the spacecraft to cut the Bimat,
closing out the photographic portion of the third mission. By
March 1, readout had been completed for 114 frames of photography,
or 54% of the total. Film advance through the readout gate was
intermittently hampered during this time, but no no photography
was lost.70
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- Then suddenly on March 4 readout ceased.
Of the 211 frames, 72 still remained to be read out, but the worst
had happened. The film advance motor had burned out, and the 72
frames remained on the take-up reel. Program engineers concluded
that an inexplicable electrical transient had scrambled the photo
system's logic, causing the motor to run out of control.
Nonetheless, 75% of the photographic data bad been transmitted to
Earth before this failure. The decision to begin readout earlier
than planned had proved very prudent indeed.71
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- Mission III photography displayed the
finest overall quality thus far obtained in the program. The
quality was due in [267] part to the use
of more diversified photographic procedures, including the use of
precisely oriented camera axis over a wide range of tilt angles
and azimuth. The exposure sequencing modes were varied and used
more extensively. Relaxation of earlier photographic constraints,
higher orbit inclination and extended stereoscopic photography
resulted in greater coverage over a wider range-of latitude and
successful photography under extreme illumination
conditions.72
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- Among other important sites Lunar Orbiter
III photographed the Surveyor
I landing area, permitting the
location and identification of the spacecraft on the Moon's
surface in Telephoto Frame 194 of Site III
Pl2a.73 This and other accomplishments proved the
reliability, accuracy, and versatility of the spacecraft in its
lunar exploration mission and gave program officials the
confidence to attempt more complex precision photography on the
two remaining missions.
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