A Fall of Moondust

He squatted down on the little metal platform, the size and shape of a manhole cover, and examined it carefully. The trapdoor valve that had been open during the piston's descent through the dust was leaking very slightly, and a trickle of gray powder was creeping round the seal. It was nothing to worry about, but Lawrence could not help wondering what would happen if the valve opened under the pressure from beneath. How fast would the dust rise up the shaft, like water in a well? Not as fast, he was quite certain, as he could go up that ladder.

Beneath his feet now, only centimeters away, was the roof of the cruiser, sloping down into the dust at that maddening thirty degrees. His problem was to mate the horizontal end of the shaft with the sloping roof of the cruiser—and to do it so well that the coupling would be dust-tight.

He could see no flaw in the plan; nor did he expect to, for it had been devised by the best engineering brains on Earth and Moon. It even allowed for the possibility that Selene might shift again, by a few centimeters, while he was working here. But theory was one thing—and, as he knew all too well, practice was another.

There were six large thumbscrews spaced around the circumference of the metal disc on which Lawrence was sitting, and he started to turn them one by one, like a drummer tuning his instrument. Connected to the lower side of the platform was a short piece of concertina-like tubing, almost as wide as the caisson, and now folded flat. It formed a flexible coupling large enough for a man to crawl through, and was now slowly opening as Lawrence turned the screws.

One side of the corrugated tube had to stretch through forty centimeters to reach the sloping roof; the other had to move scarcely at all. Lawrence 's chief worry had been that the resistance of the dust would prevent the concertina from opening, but the screws were easily overcoming the pressure.

Now none of them could be tightened any further; the lower end of the coupling must be flush against Selene's roof, and sealed to it, he hoped, by the rubber gasket around its rim. How tight that seal was, he would very soon know.

Automatically checking his escape route, Lawrence glanced up the shaft. He could see nothing past the glare of the floodlight hanging two meters above his head, but the rope ladder stretching past it was extremely reassuring.

“I've let down the connector,” he shouted to his invisible colleagues. “It seems to be flush against the roof. Now I'm going to open the valve.”

Any mistake now, and the whole shaft would be flooded, perhaps beyond possibility of further use. Slowly and gently, Lawrence released the trap door which had allowed the dust to pass through the piston while it was descending. There was no sudden upwelling; the corrugated tube beneath his feet was holding back the Sea.

Lawrence reached through the valve-and his fingers felt the roof of Selene, still invisible beneath the dust but now only a handsbreath away. Few achievements in all his life had ever given him such a sense of satisfaction. The job was still far from finished—but he had reached the cruiser. For a moment he crouched in his little pit, feeling as some old-time miner must have when the first nugget of gold gleamed in the lamplight.

He banged three times on the roof. Immediately, his signal was returned. There was no point in striking up a Morse conversation, for, if he wished, he could talk directly through the microphone circuit, but he knew the psychological effect that his tapping would have. It would prove to the men and women in Selene that rescue was now only centimeters away.

Yet there were still major obstacles to be demolished, and the next one was the manhole cover on which he was sitting-the face of the piston itself. It had served its purpose, holding back the dust while the caisson was being emptied, but now it had to be removed before anyone could escape from Selene. This had to be done, however, without disturbing the flexible coupling that it had helped to place in position.

To make this possible, the circular face of the piston had been built so that it could be lifted out, like a saucepan lid, when eight large bolts were unscrewed. It took Lawrence only a few minutes to deal with these and to attach a rope to the new loose metal disc; then he shouted, “Haul away!”

A fatter man would have had to climb the shaft while the circular lid came up after him, but Lawrence was able to squeeze against the wall while the metal plate, moving edgeways, was hoisted past him There goes the last line of dofense, he told himself, as the disc vanished overhead. Now it would be impossible to seal the shaft again if the coupling failed and the dust started to pour in.

“Bucket!” he shouted. It was already on its way down.