“Now you’re the one who doesn’t realize the problem,” the mechanic replied. “We were using heating coils, thermometers, pressure gauges, and photocells for the other stuff. Those come ready made. All I did was hook them up to a regular achronic transmitter — we couldn’t use ordinary radio because the waves would have taken ten or twelve minutes for the round trip. I didn’t make anything — just strung wires.”
“I suppose you’re right,” Ken admitted. “In that case, we may as well go back to the station and lay plans for sealing off that last cavern.” He kept a sharp look on his two companions as he said this, and succeeded in catching the glance Feth sent at the clock before his reply. It almost pleased him.
“Hadn’t we better get some photographs and measurements of the cave first?” Ordon Lee cut in. “We’ll need them for estimates on how much gas and soil will be needed, regardless of how it’s to be obtained.” Ken made no objection to this; there was no point in raising active suspicion, and he had substantiated his own idea. He was being kept away from the station intentionally. He helped with the photography, and subsequently with the direct measurement of the cave. He had some trouble refraining from laughter; affairs were so managed that the party had returned to the ship and doffed space suits each time before the next activity was proposed. It was very efficient, from one point of view. Just to keep his end up, he proposed a rest before returning to the base, and was enthusiastically seconded by the others. Then he decided to compute the volume of the cave from their measurements, and contrived to spend a good deal of time at that — legitimately, as the cave was far from being a perfect sphere. Then he suggested getting some samples of local rock to permit an estimate of digging difficulties, and bit back a grin when Feth suggested rather impatiently that that could wait. Apparently he had outdone the precious pair at their own game — though why Feth should care whether or not they stayed longer than necessary was hard to see.
“It’s going to take quite a lot of gas,” he said as the Karella lunged into the black sky. “There’s about two million cubic feet of volume there, and even the lower pressure we need won’t help much. I’d like to find out if we can get oxygen from those rocks; we should have picked up a few samples, as I suggested. We’re going to have to look over the upper area for small cracks, too— we have no idea how airtight the darn thing is. I wish we could — say, Feth, aren’t there a lot of radar units of one sort or another around here?”
“Yes, of course. What do you want them for? Their beams won’t penetrate rock.”
“I know. But can’t the pulse-interval on at least some of them be altered?”
“Of course. You’d have to use a different set every time your range scale changed, otherwise. So what?”
“Why couldn’t we — or you, anyway — set one up with the impulse actuating a sounder of some sort which could be put in contact with the rock, and time that return-echo picked up by a contact-mike? I know the impulse rate would be slower, but we could calibrate it easily enough.”
“One trouble might be that radar units are usually not very portable. Certainly none of the warning devices in this ship are.”
“Well, dismantle a torpedo, then. They have radar altimeters, and there are certainly enough of them so one can be spared. We could have called base and had them send one out to us — I bet it would have taken you only a few hours. Let’s do that anyway — we’re still a lot closer to the caves than to the base.”