A few days ago I had e-mail from a stranger who asked a great question. He was tired, he said, of pyramid conspiracy freaks who insist that human beings could not have built, or even contemplated building, the great pyramids without assistance from extra-terrestrials. What were the costs of the pyramids in terms of the Gross National Product of ancient Egypt?

I did not, and do not, know the GNP of Egypt four and a half thousand years ago, which is about when the Great Pyramid of Giza was built. However, we have current information on what went into that pyramid: more than two million blocks of stone, weighing an average of two and a half tons each. The Greek historian Herodotus stated that the construction was done by a hundred thousand men working for twenty years, but he wrote two thousand years after the pyramid was finished and there is no reason to give his words special validity. More recent and probably much better estimates can be found in L. Sprague de Camp's book, "The Ancient Engineers" (1960, reprinted 1990) which I strongly recommend. De Camp suggests a permanent staff of four thousand, supplemented during the flood season by forced labor who were farmers for the rest of the year. If the twenty-year estimate is anywhere close, building the Great Pyramid needed maybe one hundred and fifty thousand man-years of effort.

There is no evidence that the work drove the nation to bankruptcy, though proof that this can be done was offered more recently by King Louis II (or Ludwig II) of Bavaria. From about 1865 to 1885, Louis scattered extraordinary and beautiful castles about his realm. He didn't worry about cost. When he was finally declared insane in 1886, the country was at the edge of financial ruin.

Louis really was crazy. Less than a week after he was deposed, he drowned himself and his doctor, who had made the fatal mistake of going for a walk alone with his patient. Louis was succeeded by his brother Otto, who was unfortunately equally and incurably mad. On the other hand, the castles remain as one of the wonders of Bavaria, while most monarchs of the time are not remembered for anything. Maybe Louis was not as crazy as he seemed.

As you can see, I never did provide my correspondent with an actual answer. That is not too surprising, since I can't claim ancient Egypt as an area of expertise. I am, however, very interested in space development and possible space colonization, and his question led me to one of my own: What do different space projects, past, present, and future, cost in terms of GNP or GWP (Gross World Product)?

The Apollo Project offers one data point. At its absolute peak, NASA's costs approached five percent of GNP. The Hoover dam, by comparison, was built with one percent of the GNP of its day. The International Space Station, cost overruns and all, currently absorbs maybe one-twentieth of one percent of GWP.

However, neither the politically driven Apollo program nor the financially floundering space station looks like a precursor to space colonization. Colonization calls for something substantial, permanent and ultimately self-sustaining. Something, perhaps, like the "L-5 colonies" that I wrote about a few months ago. These colonies, so named because they would sit at certain points known as the L-4 and L-5 points in the Earth-Moon system, were envisaged as large rotating cylinders, complete and self-contained worlds with their own water, air, soil, and plant and animal life. The animal life would include ten thousand human colonists.

Could such colonies be built, now or maybe in the next half-century? Before the recent daunting experience of the space station, most people would have said yes - but at a price. If the people of the United States were willing to spend five percent of the GNP for twenty years, and things went well, an L-5 colony might be built. There is no evidence that people would stand for any such thing. They would, quite rightly, ask the question: Who will benefit from the colony's existence? The answer, the ten thousand colonists, is hardly good enough. The answer, possibly the whole human race, if anything happens to kill off everyone on the Earth's surface, is more disturbing than satisfactory.

So, let's give up on L-5 colonies. How about a colony on Mars? As I pointed out in a column two years ago, Mars was (and is) high on NASA's list of priorities. Although estimates by Mars enthusiasts have quoted prices as "low" as twenty billion dollars for a first manned trip to Mars and back, for a permanent colony I would be skeptical of any number less than a few trillion dollars. Once again, we would be asking for a commitment of a substantial fraction of the GNP, although it would logically be spread over fifty or a hundred years. Unlike the L-5 colony, our Mars colony has plenty of room to expand and grow in population, and it might indeed offer humanity a second chance, were utter disaster to strike here at home. Even so, I see no chance at all that the people of this country, or of the whole world, would support such a project.

Am I, then, pessimistic about the prospects for any human colony on Mars, or in the Asteroid Belt? I am not, because two factors so far unmentioned will help. First the Gross National Product and the Gross World Product, despite short-term recessions or longer-term depressions, have risen steadily for the past three hundred years. It is reasonable to expect that they will continue to do so. Second, the technology that you can buy for a fixed amount of money, even with inflation, has increased much more rapidly than the growth in GNP and GWP. If those trends continue, the cost of space colonies in absolute terms will go down, and the cost of the colonies as a fraction of GNP will go down even faster.

Can we, then, answer the question, when will people be willing to build a permanent space colony, no matter where - the Moon, Mars, Europa, the Asteroid Belt - that colony may prove to be?

I think so, and the answer is remarkably simple: We will build a colony when the cost appears small enough, relative to total government expenditures, to raise no more public outcry than farm subsidies, corporate tax breaks, and congressional pork barrels.

"Borderlands of Science" is syndicated by: