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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 Plan for Mission
II
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- [248] While Boeing
reworked the camera thermal door, the Lunar Orbiter Project Office
at Langley continued to formulate plans for the second mission.
Original planning for Mission B had only photographic data from
Earth-based telescopes and Ranger spacecraft to rely upon because
Lunar Orbiter I had not yet flown. On May 6, 1966, representatives
[249]
from Bellcomm and the Apollo, Surveyor, and Lunar Orbiter Program
offices convened at Langley for the Mission B Planning Meeting.
The information and requests which they provided enabled Langley
mission planners to set up the following guidelines for Lunar
Orbiter Mission B:
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- 1. Distributed sampling with a string of
sites in the northern part of the Apollo zone.
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- 2. Sampling of both mare and highland with
greatest number of samples in the mare.
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- 3. Sites spaced consistent with the
lighting of LEM landing constraints. (Present value of sun
elevation of 7 to 20 degrees would be used, resulting in optimum
spacing equaling 11 degrees, plus or minus 2 degrees.)
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- 4. One of the mare sites to be the
Ranger VIII impact point.
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- 5. The availability of a landed Surveyor
or any new data to necessitate a review of any mission
design.
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- 6. Mission B sites to be selected whose
terrain to the east appeared to be consistent with the Apollo
landing approach constraints, where possible.39
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- The members of the several organizations
at the meeting aided Langley officials in producing a Mission B
plan which the Lunar Orbiter Program Office in Washington
presented to the Surveyor/Orbiter Utilization Committee on June 1.
The plan had three primary goals based upon Ranger and
[250]
Earth-telescope data and performance evaluations of the Lunar
Orbiter spacecraft subsystems:
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- A. Photographic-To obtain detailed lunar
topographic and geologic information of various lunar areas to
assess their suitability for use as Apollo landing sites.
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- B. Selenodetic-To provide trajectory
information which will improve the definition of the lunar
gravitational field.
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- C. Environmental-To provide measurements
of micrometeoroid and radiation flux in the lunar environment for
spacecraft performance analysis.40
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- Apollo requirements had priority as on the
first mission. The area to be covered was a swath along the front
side of the Moon ranging from +5° to -5° latitude and
+45° to -45° longitude. Topographic considerations
affecting the mission plan dictated that Lunar Orbiter B
(Lunar Orbiter II) look for areas smooth enough for the Apollo Lunar
Module to land on. The approaches to these areas had to be free of
obstacles over a certain height to allow satisfactory performance
of the Lunar Module landing radar.41 Because the Apollo missions would operate in a
retrograde lunar orbit instead of the posigrade orbit of the Lunar
Orbiter missions, the landing approach zone would be east of the
[251]
landing site.42
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- The Lunar Orbiter Project Office at
Langley selected eleven sites pertaining to Apollo missions to be
photographed on the second Orbiter mission. In order to keep the
mission simple the spacecraft would execute a minimum number of
attitude maneuvers. There would be one photographic pass per site,
and high orbit photography would be eliminated. Lunar Orbiter II
would carry out contiguous high-resolution vertical photographic
coverage between adjacent orbits. This called for an inclination
of 11° to 12° to the lunar equator. Surface lighting
conditions had to be such that photography could detect cones of
two-meter diameter and one-half meter height and slopes of 7°
in an area of seven meters square.43
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- On September 29 the tentative Mission B
plan was amended. The photography and spacecraft performance
evaluations of Lunar Orbiter
I-in addition to further inputs
from Bellcomm, the U.S.. Geological Survey, the Army Map Service,
the Manned Spacecraft Center (Houston), NASA Headquarters Office
of Manned Space Flight, and the Surveyor Project Office-confirmed
tentative mission objectives for the second Lunar Orbiter flight
more than they altered them. As of October [252] 26 these
objectives were:
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- Primary
- To obtain, from lunar orbit, detailed photographic information
of various lunar areas, to assess their suitability as landing
sites for Apollo and Surveyor spacecraft, and to improve our
knowledge of the Moon.
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- Secondary - To provide precision trajectory information for
use in improving the definition of the lunar gravitational
field.44
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- To provide measurements of micrometeoroid
flux and radiation dose in the lunar environment, primarily for
spacecraft performance analysis.
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- During the process of site selection for
the second Orbiter mission a hypothesis based upon Earth-telescope
photography and the very useful Ranger VII pictures
exerted a particular influence on the choice of sites. Data from
these two earlier sources tended to show that bright rays
extending from younger craters were actually heavily cratered,
making landings very hazardous or impossible in such areas. To
test this, Lunar Orbiter
I had photographed sections in
lightly rayed areas. Specifically, photographs of Site A-3 in Mare
Tranquillitatis revealed smooth areas where a Lunar Module could
land. Orbiter I Frame M-100 of Site A-3 showed an area in a light
ray where cratering was insufficient to rule it out as a landing
site. The ray in this photograph was faint and probably had its
origins in [253] the crater Theophilus but had subsequently been
filled in.45
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- Planners concluded from Orbiter I photography
that some ray areas were possibly smooth. Moreover, photography
from the first Orbiter had actually previewed certain targets in
the second mission. Thus planners decided to change several sites
in Mission B and to have Lunar
Orbiter II look at the ray areas
between the lunar craters Copernicus and Kepler, extending north
of the western Apollo zone. The Mission B plan was thus
substantially revised as a result of the divergences between
Ranger VII and Lunar Orbiter
I photographs of crater
rays.46
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