So they had cause to be loyal nationals, each to his own. And each took care, as he had all his life, that no breath of suspicion sully his name or place in doubt (by a wary government) his suitability for the work he had to do. And if on rare and most private occasions, either one of them thought briefly, wistfully, of the advantages of a united approach to the Dream--he knew well enough that for _other_ men, Space was no dream at all, but a prize enhanced--if not created--by competition. The isolation, security measures, and endless duplication of research and planning were, _realistically_, necessary. This attitude was of course easier to maintain on the Moon than on Earth. Fifteen hundred miles of rugged lunar terrain, and the exigencies of rocket fuel economy, kept physical contact between the domes down to a minimum. Two hundred fifty thousand miles of empty space, and the economics of human existence on the Moon, kept political contact with the home governments down to a minimum too: on the Moon, a really rigid security could be sustained with almost no worry about infiltration, no possible worry about associations, and no pettyfogging annoyances from suspicious, ambitious policemen or politicians. The prevailing state of by-mutual-consent _laissez-faire_ isolation was such an inherent fabric that Dr. Chen and Dr. Christensen had never even met personally. There had simply been no occasion. For that matter, up till the day of Johnny Wendt’s return, the men on either staff who had even _seen_ the other dome could be counted on two hands; none had ever been further inside the other than the landing lock--and that only on the occasions of the inevitable minor emergencies that called for humane sharing of survival (_not_ scientific) equipment. With the exception of these instances, USAA ships made it a point not even to fly inside a line-of-sight of Plato Crater, and Red pilots stayed equally clear of Playfair. The only modification of this “natural security” status that had occurred between the times that the two domes went up, in ’69, and the orbiting of the _Moon Messenger_ in ’74, was when an outraged AA Congress learned that the Reds had succeeded in sending a ship to Mars without any previous knowledge at Dollars Dome. But even then, no real attempt was made at an Intelligence network operating directly between the domes; it just wasn’t worth the waste of oxygen on a Dome resident doing less than a full-time job of research or development. The money authorized as a result of the indignant Congressional Investigation went into tightening and improving existing infiltrations on Relay Station, the 400-mile Earth satellite, and at World Dome.