I agree with Kevin J. Sweeney that the proposed half-trillion-dollar-plus manned mission to Mars "might anger rather than inspire" and that the greatest challenge facing us today "centers around environmental issues". However, the key to our "down to Earth" problems lies in space.

As generally recognized, the greatest threat to our environment comes from our energy problems. Burning fossil fuels, limited in supply, is the primary source of our urban air pollution and also of the carbon dioxide that is exaggerating the atmosphere's Greenhouse Effect, threatening global warming and catastrophic climatic change. Nuclear power plants are potentially explosive in the short-run, and nuclear waste is lethally toxic for the long-run. The one and only virtually unlimited, clean, and safe source of power for our planet is solar energy -- the same sunlight that, through photosynthesis, has ultimately powered virtually all life on Earth from the beginning.

As outlined in the Times (March 7, 1989) by Gerard K. O'Neill, of the National Commission on Space, the most effective way to harness solar power is to construct (from materials lifted almost "weightlessly" from the moon) solar-energy satellites -- orbiting the planet and converting the unblocked light from our star, the Sun, into electricity, radio-waved down to Earth.

In addition to inestimable environmental savings, trillions of dollars' worth of energy sales await the masters of this high-orbit technology; and the undoubtedly formidable initial investment, creating countless down-to-Earth jobs, would require multi-national co-operation -- even greater than for a mission to Mars (with a mineralogical payoff, from asteroids, still farther off in space).

And perhaps that would be a greater objective to achieve than even the economic and environmental rewards -- people around our world striving together for a peaceful, practical international purpose.