Although the lunar work environment is extreme by any terrestrial
standards,
with the exception of major solar particle events, it is
highly predictable.
Because the Moon has no appreciable atmosphere and, necessarily, no
clouds, the amount of sunlight falling on a given spot is
determined solely by the site latitude, the Moon's orbital motion
around the Earth, and the Earth's motion around the Sun.
Temperature
cycles can be predicted with high accuracy far into the future, which
can greatly simplify the thermal design of equipment
and structures.
Most of the lunar surface is covered with a layer of impact
debris, called the regolith, which is usually several meters
thick and most of it very fine. During future lunar operations,
the regolith can be a
curse - in the form of fine, invasive, troublesome dust particles. It
can also be a
blessing as a firm foundation for construction projects and
as a source of some construction materials and of shielding material
for protection against solar
energetic particle events.
The lunar surface is littered with impact craters. For the most
part, the craters are randomly distributed. Larger craters are
much less numerous than smaller ones. Because of the large number of
craters and the frequency of overlap, Lunar Rover crews found the
driving to be "sporty". Although any particular patch of ground
has been hit many times over the course of lunar history, on
human timescales impacts are infrequent.
The Moon's surface gravity is 1/6th that of
Earth. Weaker surface gravity means that vehicles and structures
need not be as solidly built as on Earth. During Apollo, although
the astronauts
had to wear pressure suits when they were outside the Lunar Module,
they
found that (1) running and many other forms of physical activity were
easier than on Earth, (2) they could take advantage
of objects falling much more slowly than they do on Earth;
and (3), unlike the weightless environment of a
spacecraft in free
flight, they could put an object down on a flat surface and know that
it
would stay put. Above all, the Apollo astronauts thought 1/6th
gravity was great fun.
Shadows on the Moon can be darker than on Earth but, in most
circumstances there is enough light scattered off the lunar surface to
give good visibility, particularly with protective visors raised.
The Rover-mounted, auto-irised TV camera had no trouble seeing into
shadows,
provided that sufficient zoom was available to keep sunlight surfaces
out of the field-of-view. All of the landings occurred early in
the local morning and looking toward the east was difficult when the
Sun was too low to be blocked by the top sunshade of the visor
assembly. When the Sun
was low in the east, the view to the west was washed out because of a
combination of factors: (1) strong reflections back toward the
Sun by the numerous small rock fragments; (2) the uniform grey color;
and (3) the fact that shadows were hidden by the rocks that cast
them. Visibility perpendicular to the sunline was excellent.
Because the Moon has no appreciable magnetic field, energetic solar
particles and galactic cosmic rays reach the surface unimpeded. Excluding major solar particle events, exposure to the normal background from galactic cosmic rays during a six-month lunar stay represents a risk of a fatal cancer later in life that is comparable to the risk of fatal accidents inherent in space flight.
Major solar events are relatively rare - at most, a few per solar cycle
- but could be severely debilitating or even fatal to anyone who is not
adequately protected, preferably in a buried shelter. Warning
times may be as short as 30 minutes. During all of Apollo, the
only such events occurred on 4 August 1972, which was four months after
Apollo 16 and four months before Apollo 17.
________
Some aspects of the lunar work environment are covered in more detail
in the subpages that follow. Comprehensive discussions of these
and other topics can be found the
authoritative
Lunar
Sourcebook: A User's Guide to the Moon,
edited by
Grant H. Heiken, David T. Vaniman, and Bevan M. French, Cambridge
University Press, 1991 and in the references it contains.