The Lunar Environment

The differences between the Earth and Moon appear clearly in comparisons of their physical characteristics (Table 3.1). The Moon is indeed an alien environment. While these differences may appear to be of only academic interest, as a measure of the Moon’s “abnormality,” it is important to keep in mind that some of the differences also provide unique opportunities for using the lunar environment and its resources in future space exploration. Despite these differences, there are strong bonds between the Earth and Moon. Tidal resonance between Earth and Moon locks the Moon’s rotation with one face (the “nearside”) always toward Earth, the other (the “farside”) always hidden from Earth. The lunar farside is therefore totally shielded from the Earth’s electromagnetic noise and is—electromagnetically at least—probably the quietest location in our part of the solar system. The Moon has also been moving away from Earth over time, because the dissipation of tidal energy by bottom friction in the Earth’s seas (especially in shallow seas) has gradually slowed the Earth’s rotation (e.g., Lambeck, 1975). To keep the angular momentum of the Earth-Moon system constant, the Moon has been moving slowly outward at a rate of a few centimeters per year. The relationships between the Earth and Moon in origin, composition, and orbital dynamics are as important for the basing of people and equipment on the Moon as they are for scientific understanding. However, in considering routine terrestrial processes transplanted to the Moon, it is primarily the many differences in Table 3.1 that stand out. On the Moon the most obvious environmental factors that concern people are extreme temperature fluctuations, low gravity, and the virtual absence of any atmosphere. Other environmental factors are not so evident. Of these the most important is ionizing radiation, and much of this chapter is devoted to the details of solar and cosmic radiation that constantly bombard the Moon. Of lesser importance, but necessary to evaluate, are the hazards from micrometeoroid bombardment, the nuisance of electrostatically charged lunar dust, and alien lighting conditions without familiar visual clues. To introduce these problems, it is appropriate to begin with a human viewpoint—the Apollo astronauts’ impressions of environmental factors that govern the sensations of working on the Moon.