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Overview of the Lunar Work Environment

Copyright © 2007 by the Editors of Working on the Moon.
Last revised 18 February 2008.

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, particuarly 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, the normal background from galactic cosmic rays produces equivalent doses of about 2 rem/month at solar maximum and 4 rem/month at solar minimum.  These are comparable with US limits of 5 rem/yr for people who regularly work with radiation sources.  Careful attention to shielding can reduce exposures.  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, perferably 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 monhts 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.  The Sourcebook is available on DVD from the Lunar and Planetary Institute.



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