Walt looked up from his slide rule. "Fifty-two thousand, two hundred and twenty-four miles," he said. "Just what I was about to say," grinned Don. "But why do you always get there second with your genius?" complained Walt with a pseudo-hurt whine. "So how to establish it?" "Can't use space radar for range," grunted Channing. "That would louse up the receiver. We've got everything shut off tight, you know. How about some visual loran?" "Yipe!" exploded Walt. "How?" "I'd suggest an optical range finder excepting that the base-line of three miles--the length of Venus Equilateral--isn't long enough to triangulate for that fifty-two thousand--" "Two hundred and twenty-four miles," finished Walt with a grin. "Proceed, genius, with caution." "So we mount a couple of mirrors at either end of the station, and key a beam of light from the center, heading each way. When the pulses arrive at the space flitter at the same time, he's in position. We'll establish original range by radar, of course, but once the proper interval or range is established, the pilot can maintain his own position by watching the pulsed-arrival of the twin-flickers of light. Just like loran, excepting that we'll use light, and we can key it so it will run alternately, top and bottom. To maintain the proper angle, all the pilot will have to do is to keep the light alternating--fluently. Any overlapping will show him that he's drifted." "Fine!" glowed Walt. "Now, how the devil long will it take?" "Ask the boys, Walt," suggested Don. Walt made a canvass of the machine shop gang, and came back, saying: "Couple of hours, God willing." The mounting of the mirrors at either end of the station took little time. It was the amount of detailed work that took time; the devising of the interrupting mechanism; and the truing-up of the mirrors that took the time. Then it became evident that there was more. There were several hundred doorways centered on the axis of Venus Equilateral that must be opened, the space cleared of packing cases, supplies, and in a few cases machinery had to be partially dismantled to clear the way. A good portion of Venus Equilateral's personnel of three thousand were taken off their jobs, haled out of bed for the emergency, or made to work through their play period, depending upon which shift they worked. The machinery could be replaced, the central storage places could be refilled, and the many doors closed again. But the central room containing the air plant was no small matter. Channing took a sad look at the lush growth of Martian saw grass and sighed. It was growing nicely now, they had nurtured it into lusty growth from mere sprouts in trays and it was as valuable--precisely--as the lives of the three thousand-odd that lived, loved, and pursued happiness on Venus Equilateral. It was a youthful plant, a replacement brought in a tearing hurry from Mars to replace the former plant that was heaved out by the well-meaning Burbank.