Other than that, they were mathematically safe--if they depended on the laws of chance. No ship moving through the Asteroid Belt would dare to move at any decent velocity without using radar, so the people on this particular lump of planetary flotsam would be able to spot a ship's approach easily, long before their own weak detection system would register on the pick-ups of the approaching ship. The power and range needed by a given detector depends on the relative velocity--the greater that velocity, the more power, the greater range needed. At one mile per second, a ship needs a range of only thirty miles to spot an obstacle thirty seconds away; at ten miles per second, it needs a range of three hundred miles. The man who called himself Stanley Martin had carefully plotted the orbit of this particular planetoid and then let his spaceboat coast in without using any detection equipment except the visual. It had been necessary, but very risky. Had the people here seen his boat? If so, had they recognized it, in spite of the heavy camouflage? And, even if they only suspected, what would be their reaction? He waited. It takes nerve and patience to wait for thirteen solid hours without moving more than an occasional flexure of muscles, but he managed that long before the instrument case waggled a meter needle at him. The one relieving factor was the low gravity; on an asteroid, the problem of sleeping on a bed of nails is caused by the likelihood of accidentally throwing oneself off the bed. The probability of puncture or discomfort from the points is almost negligible. When the needle on the instrument panel flickered, he got to his feet and began moving. He was almost certain that he had not been detected. Walking was out of the question. This was a silicate-alumina rock, not a nickel-iron one. The group that occupied it had deliberately chosen it that way, so that there would be no chance of its being picked out for slicing by one of the mining teams in the Asteroid Belt. Granted, the chance of any given metallic planetoid's being selected was very small, they had not even wanted to take that chance. Therefore, without any magnetic field to hold him down, and only a very tiny gravitic field, the man had to use different tactics. It was more like mountain climbing than anything else, except that there was no danger of falling. He crawled over the surface in the same way that an Alpine climber might crawl up the side of a steep slope--seeking handholds and toeholds and using them to propel himself onward. The only difference was that he covered distance a great deal more rapidly than a mountain climber could. When he reached the spot he wanted, he carefully concealed himself beneath a craggy overhang. It took a little searching to find exactly the right spot, but when he did, he settled himself into place in a small pit and began more elaborate preparations.