ON the 25th anniversary of humanity's first extraterrestrial footfall, it's worth revisiting a great space flight prophet.
The late Krafft A. Ehricke was one of the German rocket scientists who helped put the American space program into orbit after World War II. He wasn't well known to the general public. Yet he was the expert to whom other Western experts most often turned for an overarching, but technically sound, vision of how manned space flight might unfold.
To Ehricke, that unfoldment was nothing less than the next crucial phase in the evolution of life in our solar system. And the exploration and settlement of the moon was logically the first stage of that development. He detailed that vision in his last major public address, given at the National Academy of Sciences in Washington, D.C., ten years ago. He called it ``the extraterrestrial imperative.''
In Ehricke's view, Earth is not merely an oasis in an otherwise lifeless solar system. It is a cradle - a home base - for organic life that is surrounded by a wealth of extraterrestrial resources. To survive and evolve, life that arose on Earth must tap those resources.
The first crisis that forced this outreach occurred three to four billion years ago. That's when Earth's primitive life forms could no longer thrive by gobbling up goodies from the ``primordial soup'' from which they arose or by eating each other.
Earthly life ``learned'' how to use the abundant extraterrestrial energy of sunshine to make needed chemicals from carbon dioxide and water. Since then, virtually all life on Earth -
including human life - has been based ultimately on photosynthesis.
Ehricke saw the next crisis that would force an extraterrestrial outreach as the leading challenge of our own time.
He noted that the biosphere generally uses about two dozen of the hundred plus chemical elements and continuously recycles them. Humans have learned to use the whole periodic table of elements and can't recycle all of them.
The pressure humans are putting on Earth's resources is more than the planet can bear.
Ehricke believed humans must begin to use the energy, mineral, and living-space resources of the larger solar system to continue to grow and evolve.
The key to doing this - the analogue to photosynthesis - he called ``information metabolism,'' which is the ability to gain knowledge and to use that knowledge to acquire and develop resources.
This ability has brought humanity to its present point in history. It will, in Ehricke's view, now enable humans to develop resources beyond Earth.
He saw the moon as the training ground for doing this. It's on our doorstep. It has resources for rocket fuel and building materials. The moon has little or no water. But it has plenty of oxygen which, together with hydrogen, forms water. Carrying hydrogen - the lightest element - from Earth to make water or rocket fuel would be relatively cheap.
Using lunar materials to build the infrastructure for space development would be cheaper than bringing them from Earth. That's because the moon's gravity is only a sixth of that of Earth so it takes much less energy to move material off the moon than it does to escape Earth's gravity. Lunar orbiting satellites would capture solar energy and beam it to the surface to power lunar development.
Ehricke summed up his vision in a sentence. ``If God had wanted a species, such as this, to become a space-faring species, he would have given them a moon.'' That's not a bad motto for space planners of the 21st century.