Geoscience Reference
In-Depth Information
equally successful and proved that the surface of the Moon would bear a heavy
weight. Moon dust proved no more real than manbats. This life-and-death question
answered, mission planners could program
Surveyor V
and beyond for science.
The purpose of the missions was to learn about the geology and chemistry of the
Moon. But how to do so before it was possible to return a sample to Earth? The
NASA team invented an instrument called an “alpha-scattering surface analyzer.”
It irradiated the surface beneath
Surveyor
with the alpha particles that Rutherford
had long ago discovered, a use that even he could not have imagined. A detect-
or in
Surveyor
measured the energy spectrum induced by the alphas and continu-
ously transmitted the data back to Earth. From the details of the spectrum, scient-
ists could estimate the abundances of the major elements in the lunar soil, which
would be good enough to tell whether it had come from volcanic basalt.
Surveyor V
had landed, and not by accident, in Mare Tranquillitatis, only
twenty-five kilometers from what in July 1969 would become Tranquility Base.
No sooner were the first results of the chemical analysis in than cold-mooner Urey
reflected unhappily, “It's basalt, isn't it?” He knew that basalt is not a primordi-
al rock but forms when the interior of a body melts and differentiates. Thus the
presence of basalt meant that the Moon had once been hot enough to melt. A few
dayslater,Ureyhadrecoveredhisequanimityandgoodhumor,remarking,“maybe
Mother Nature knows best.”
5
Surveyor and subsequent missions found that over billions of years, myriad im-
pacts large and small had churned—or gardened, in Urey's phrase—the surface of
the Moon into a hodgepodge of debris. Even so, the surface appeared firm enough
to support a spacecraft and its precious cargo. A manned landing thus appeared
feasible, but the question remained as to the best place to make it. To answer re-
quired a much higher photographic resolution and a more comprehensive view of
the Moon than could be provided by spacecraft crashing into it or landing on it.
“
Surveyor
had to land 'blind' . . . no one was willing to take a similar chance with
Apollo
,” as Don Wilhelms recalled (153).
Along with Ranger and Surveyor, NASA had planned Lunar Orbiter missions
to provide the needed eyesight by placing a spacecraft in continuous orbit around
the Moon and photographing the entire surface with a resolution, clarity, and cov-
erage that gave a better view of the Moon than anyone had ever had of the Earth.
The first three Orbiter missions succeeded in thoroughly photographing thirty-two
possible Apollo landing sites, allowing the planners toprogram the last twomainly
for broad coverage and for science.
Lunar Orbiters 4
and
5
photographed almost
the entire surface of the Moon, in the process discovering the gigantic Orientale
basin, a bull's-eye nearly a thousand kilometers wide on the far western edge. But
