“No; we have found several, very similar in structure, along this cliff, and there are probably others with no openings into them. I suppose they could be located by echo-sounders if we really wanted to find them.”
“It might be a good idea to try that,” Ken pointed out. “A cave whose only entrance was one we had drilled would be a lot easier to keep airtight than this thing.” Feth and Lee grunted assent to that. The latter added a. thought of his own. “It might be good if we could find one well down; we could be a lot freer in drilling — there’d be no risk of a crack running to the surface.”
“Just one trouble,” put in Feth. “Do we have an echo-sounder? Like Ken on his soil analysis, I have my doubts about being able to make one.” Nobody answered that for some moments.
“I guess I’d better show you some of the other caves we’ve found already,” Lee said at last. No one objected to this, and they retraced their steps to daylight. In the next four hours they looked at seven more caves, ranging from a mere hemispherical hollow in the very face of the cliff to a gloomy, frighteningly deep bubble reached by a passageway just barely negotiable for a space-suited Sarrian. This last, in spite of the terrors of its approach and relative smallness, was evidently the best for their purpose out of those examined; and Lee made a remark to that effect as they doffed space suits back in the Karella.
“I suppose you’re right,” Ken admitted, “but I’d still like to poke deeper. Blast it, Feth, are you sure you couldn’t put a sounder together? You never had any trouble with the gadgets we used in the torpedoes.”
“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.”
“It’s easier to work in the shop; and anyway, if we go as far underground as this idea should let us — supposing it works — we might as well scout areas closer to the base, for everyone’s convenience.” Ordon Lee contributed the thought without looking from his controls.
“Do you think you can do it?” Ken asked the mechanic.
“It doesn’t seem too hard,” the latter answered. “Still, I don’t want to make any promises just yet.”
“There’s a while yet before that suit comes back. We can probably find out before then, and really have some material for Drai to digest. Let’s call him now — maybe he’ll have some ideas about soil.”
The eyes of the other two met for a brief moment; then Lee gestured to the radio controls,
“Go ahead; only we’ll be there before you can say much.”
“He told me you were going to manufacture soil,” reminded Feth.
“I know. That’s why I want to talk to him — we left in too much of a hurry before.” Ken switched on the radio while the others tried to decide whether or not he was suspicious about that hasty departure. Neither dared speak, with Ken in the same room, but once again their eyes met, and the glances were heavy with meaning.
Drai eventually came to the microphone at the other end and Ken began talking with little preliminary.
“We’ve made measurements of the smallest cave we can find, so far at least, and figured out roughly how much air you’re going to need to fill it. I can tell you how much soil you’ll need to cover the bottom, too, if you plan to use all of it. The trouble is, even if I can analyze the soil — even as roughly as I did the air — you’re facing a supply problem that runs into tons. I can’t make that much in the laboratory in any reasonable time. You’re going to have to get it ready-made.”
“How? We can’t land a person on Planet Three, let alone a freighter.”
“That we’ll see presently. But that’s not the suggestion I wanted to make — I see we’re nearly there, so we can finish this chat in person. Think this over while we’re going in: whatever sort of atmosphere a planet may have, I don’t see how the soils can be too different — at least in their principal constituents. Why don’t you get a shipload of Sarrian soil?” Drai gaped for a moment.
“But — bacteria—”
“Don’t be silly; nothing Sarrian could live at that temperature. I admit it would be safer to use soil from Planet Three, and we may be able to. But if we can’t, then you have my advice, if you’re interested in speed — even if I knew the composition, it would take me a lot longer than a week to make a hundred tons of dirt!” He broke the connection as the Karella settled to the ground.