The easiest way to irritate a space exploration advocate is to ask the question, "Moon, or Mars?" The best way to make amends is to answer the question yourself, "Moon, and Mars!" In a world of staggering financial resources, why should humanity be forced to pick one or the other?
Each destination has its appeals. If you want to live in space, how should you decide where to park your space-trailer?
The foolish way would be to rank each destination according to how easy it is to reach. Using this criteria (and leaving out the Earth), the proper order would be the Moon, near-Earth asteroids, and then Mars.
Yet how many people decide where they want to live based solely upon proximity to where they already live? If people thought like this, no one would ever move at all. The easiest destination would always be your current house, apartment, or park bench!
Obviously, we need a way to make a smarter decision. How about choosing a destination based upon where you want to live, what you want to do there, or the cost of living there? Using any of these criteria, the proper order of destinations in the inner solar system for most space-immigrants would be: Mars, near-Earth asteroids, and the Moon.
Let's take a closer look at the distance argument. The Moon is the closest destination, and that proximity is its greatest advantage. It only takes three days for a cargo of humans or supplies to reach the Moon. Near-Earth asteroid missions would take weeks to months (depending upon which asteroid is chosen), and Mars would take six to nine months.
The close proximity of the Moon is also its greatest disadvantage. The Apollo program was conveniently canceled because we had no need to establish any infrastructure or permanent residence on the Moon. Imagine President Nixon trying to cancel the Apollo program if it would take a crew of twenty researchers two years and mega-space-bucks to return home! If we want a permanent space exploration program, rather than a flag-and-footprints program that meets the whims of whatever politician has the most clout, then the proximity of the Moon is a huge liability.
Still, that proximity exists, so we might as well use the Moon as a way-point, a college-dorm, or some other place of temporary residence until we're able to live someplace nicer. The biggest disadvantage to living on Mars is that our high-tech space-habitat might break. If we can use the Moon as a test-bed for developing habitats durable enough to survive for years on the Moon, then we'll be better prepared for living on Mars. This argument assumes that we are not willing to accept any personal risk when we move to Mars, which is a shaky proposition at best.
NASA's current Vision for Space Exploration (VSE) uses the above argument as a motivation for exploring the Moon and returning human explorers there. The VSE is under constant attack, however, from people who want to twist the argument to their own purposes. The most-vocal twisters are people who want the Moon to be humanity's final destination. Many Lunatics (as Moon-worshipers like to call themselves) would like to construct massive lunar bases, energy production facilities, mining camps, telescopes, mass-driver facilities, roads, spaceports, hotels, etc, etc, etc.
To be honest, there are some strong arguments in favor of taking this approach. For example, producing energy on the Moon has the potential to solve many difficult terrestrial problems, like global warming and fossil-fuel depletion. These are extremely worthy goals... but not for NASA! If we expect NASA to warp their VSE to include these things, the cost of the program will skyrocket, and we'll never reach Mars or the asteroid belt. A far better solution is for NASA to research the basic equipment and procedures, learning the craft of living on the Moon. Then they should get out of the way of private industry. The Moon should become an extention of the Earth, with corporations responsible for energy production, mining, telescopes, hotels, etc.
The real issue with NASA's getting bogged down on the Moon is cost, as is mentioned above. Cost is always driven by complexity. A base on the Moon will be far, far more complex to run and supply than a base on Mars. The Moon is an amazingly harsh place. Extreme day/night temperature swings, a hard-vacuum surface, razor-sharp dust particles, scarcity of carbon, hydrogen, and nitrogen, two-week day/night light cycles, and constant hard-radiation bombardment are among the lengthy list of complex environmental factors that home-builders will need to overcome.
Each lunar environmental factor poses a formidable challenge. For example, the two-week day/night cycle will make local crop growth extremely difficult. As a result, a Moonbase will need a constant influx of expensive supplies (food, plastics, organics, etc) from Earth. With this Achilles Heel, the base will be one major accident away from total failure for decades after settlement, or longer.
A base on Mars will suffer from some of the environmental complexities listed above, but to a lesser extent. Small, weathered dust grains will be a nuisance, as will be the low atmospheric pressure, relatively minor day/night temperature swings, reduced sunlight (but Earth-like light cycles), and possible radiation bombardment during rare solar flares. The Earth-like day/night cycles will make local crop growth feasible. Plastics, other building materials, or other processed goods can be refined from local in-situ elements. Requirements for resupply from the Earth should be an order of magnitude less than for a Moonbase.
But what about the greater cost of sending initial supplies to Mars? It turns out that pound-for-pound, sending a box of Twinkies to Mars is cheaper than sending it to the Moon. A Mars Twinkie-ferry can be equipped with an aeroshell that allows it to use the atmosphere of Mars for braking and descent. In contrast, expensive, heavy rocket fuel is needed for braking and descent on the Moon. As long as a Twinkie can survive the six month journey, junk food will always be a greater luxury on the Moon than on Mars.
The economics of Moon/Mars bases can be debated ad-nausium, with adjustments made for more-efficient bases near the lunar poles, discovery of polar ice on the Moon or equatorial ice on Mars (or lack there-of), Earth-Moon or Earth-Mars "cycler" supply ferries, space elevators, etc. However, the basic, undeniable fact for you to take away from this whole discussion is the following:
The local resources that make Mars an attractive place to explore (water, atmosphere, etc) are the same resources that make living on Mars safer and cheaper.
Or, put another way, the Moon is a slag heap, and it always will be. I don't know many people who want to live atop a slag heap, but you can't beat the view. Mars is a living, breathing, dripping planet, where life will soon flourish (if it doesn't already).
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"From the darkness, a voice whispered, "You should not be here." "
Chapter 1