As I began my walk this morning, just after six a.m., I looked up and saw a beautiful full moon hanging low in the early morning sky. A great sadness swept over me as I reflected that it was now forty-five years, half a lifetime and more, since the last human had walked on the surface of the moon. Those below middle age have never known the thrill of following reports that one of our species was walking on the moon. Since then, we have spent hundreds of billions of dollars in fruitless, destructive wars, the inequality of our society has grown ever more grotesque, and yet it has not proved possible to mount one more manned space flight to our nearest solar system neighbors. Had we devoted a tenth of the resources we have wasted killing, we could by now have sent men and women to Mars, and brought them back.