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DESTINATION MOON: A History of the
Lunar Orbiter Program
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- CHAPTER X: MISSIONS IV AND V: THE
LUNAR SURFACE EXPLORED
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- Preparing for the Fourth
Mission
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- [269] As approved by
the Ad Hoc Surveyor/Orbiter Utilization Committee on May 1, 1967,
Mission IV would attempt to accomplish some of the objectives not
directed towards fulfilling Apollo needs. Specifically it would
"perform a broad systematic photographic survey of lunar surface
features in order to increase the scientific knowledge of their
nature, origin, and processes, and to serve as a basis for
selecting sites for more detailed scientific study by subsequent
orbital and landing missions."1
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- This mission, unlike the first three,
required that Lunar Orbiter
IV fly a nearly polar orbit. In
such an orbit [270] the spacecraft would acquire contiguous
photographic coverage of a minimum of 80% of the front side at 50
to 100 meters resolution. It would photograph as much of the
Moon's far side as possible at the best possible resolution. The
spacecraft's photographic subsystem would carry enough film for
212 frames, and ground control planned to read out all photography
in the priority mode immediately after processing as a precaution
against any mechanical failure in the subsystem. A final readout
would be available if necessary.2
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- In preparation for the fourth mission the
Lunar Orbiter Project and Program Offices conducted a flight
readiness review on April 13, 1967. On March 13, Spacecraft 7 (the
fourth flight spacecraft, or Lunar
Orbiter IV) had been removed from
storage at the Kennedy Space Center to begin Hangar S integration
and checkout tests. Launch readiness was scheduled for May 4. and
no problems were encountered during the Hangar S
activities.3 The flight readiness review found Lunar Orbiter IV and
the backup (Spacecraft 3) ready for launch.4
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- Because the fourth Orbiter would fly a
high polar orbit, it would be exposed to the Sun almost the entire
[271]
mission, necessitating certain changes on the spacecraft. A
modified charge-controller component was installed to reduce the
rate of charge in the power system. Boeing engineers covered about
20% of the exterior of the equipment deck with mirrors to increase
its heat rejection capability. A damaged micrometeoroid detector
was removed and another unit installed. Finally the Inertial
Reference Unit was removed for replacement of a failed capacitor.
After reinstallation it successfully completed two attitude
control system tests.5
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- During the weeks before the fourth launch
the Program Manager showed some concern over the failure of NASA's
Applications Technology Satellite (ATS II) to achieve its planned
circular orbit around the Earth on April 6.6 NASA officials
attributed the improper orbit to failure of the Agena rocket to
reignite in orbit. Unofficially ATS program management said the
cause for the reignition failure was failure of the Agena's
Propellant Isolation Valve (PIV) to close after the first burn.
Scherer hoped the PIV for the Lunar Orbiter IV Agena
would test out successfully before April 27, the planned date for
the mating of the Agena with the Atlas [272]
booster.7 Lewis Research Center personnel responsible for the
Agena took corrective actions and installed a reworked valve in
time for the launch. The reinstallation took less than one month
to complete, and it did not jeopardize the launch date.
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- Two areas involving previous mission and
ground test problems also pertained to the successful performance
of the fourth and fifth missions. The traveling-wave-tube
amplifier aboard Lunar Orbiter
II had experienced high helix
current. Ultimately it had failed to turn on during the final
readout phase, and some data were lost. The TWTA onboard
Lunar Orbiter III had also experienced overheating from high helix
current and power output variations from temperature changes.
Worse yet, the TWTA in the ground spacecraft for the Mission D
Simulation Test failed to perform successfully under mission
conditions. The component was undergoing close examinations to
determine the mode of failure. A delay of the fourth mission would
hinge upon the seriousness of the test findings and the difficulty
in resolving the problem.8
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- Failure in the photographic subsystem
presented the other area of questionable spacecraft performance.
Readout [273] problems had marred the success of Lunar Orbiter III
with unwanted repetition in readout and the inability of the film
transport system to move film. Program investigators had not
pinpointed the causes of these failures. However, the ten-day
Mission D Simulation Test, just completed on April 12, partially
compensated for these failures. During the test no problems
involving readout had occurred, increasing the likelihood of a
successful fourth mission.
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