provide ideas and technical knowledge; it was his private brain trust.
Only half of its dozen members were physically present; the rest were scattered over Moon, Earth, and space. The soilphysics expert on Earth was at a disadvantage, for owing to the finite speed of radio waves, he would always be a second and a half in arrears, and by the time his comments could get to the Moon, almost three seconds would have passed. He had accordingly been asked to make notes and to save his views until the end, only interrupting if it was absolutely necessary. As many people had discovered, after setting up lunar conference calls at great expense, nothing hamstrung a brisk discussion more effectively than that three-second time lag.
"For the benefit of the newcomers," said Lawrence, when the roll call had been completed, "I'll brief you on the situation. Selene is fifteen meters down, on a level keel. She's undamaged, with all her equipment functioning, and the twentytwo people inside her are still in good spirits. They have enough oxygen for ninety hours - that's the deadline we have to keep in mind.
"For those of you who don't know what Selene looks like, here's a one-in-twenty scale model." He lifted the model from the table, and turned it slowly in front of the camera. "She's just like a bus, or a small aircraft; the only thing unique is her propulsion system, which employs these wide-bladed, variable-pitch fans.
"Our great problem, of course, is the dust. If you've never seen it, you can't imagine what it's like. Any ideas you may have about sand or other materials on Earth won't apply here; this stuff is more like a liquid. Here's a sample of it."
Lawrence picked up a tall vertical cylinder, the lower third of which was filled with an amorphous gray substance. He tilted it, and the stuff began to flow. It moved more quickly than syrup, more slowly than water, and it took a few seconds for its surface to become horizontal again after it had been disturbed. No one could ever have guessed, by looking at it, that it was not a fluid.
"This cylinder is sealed," explained Lawrence, "with a vacuum inside, so the dust is showing its normal behavior. In air, it's quite different; it's much stickier, and behaves rather like very fine sand or talcum powder. I'd better warn you-it's impossible to make a synthetic sample that has the properties of the real thing. It takes a few billion years of desiccation to produce the genuine article. If you want to do some experimenting, we'll ship you as much dust as you like; heaven knows, we can spare it.
"A few other points. Selene is three kilometers from the nearest solid land - the Mountains of Inaccessibility. There may be several hundred meters of dust beneath her, though we're not sure of that. Nor can we be quite sure that there will be no more cave-ins, though the geologists think it's very unlikely.
"The only way we can reach the site is by dust-ski. We've two units, and another one is being shipped round from Farside. They can carry or tow up to five tons of equipment; the largest single item we could put on a sledge would be about two tons. So we can't bring any really heavy gear to the site.
"Well, that's the position. We have ninety hours. Any suggestion? I've some ideas of my own, but I'd like to hear yours first."
There was a long silence while the members of the committee, scattered over a volume of space almost four hundred thousand kilometers across, brought their various talents to bear on the problem. Then the Chief Engineer, Farside, spoke from somewhere in the neighborhood of Joliot-Curie.
"It's my hunch that we can't do anything effective in ninety hours; we'll have to build special equipment, and that always takes time. So - we have to get an air line down to Selene. Where's her umbilical connection?"
"Behind the main entrance, at the rear. I don't see how you can get a line there and couple it up, fifteen meters down. Besides, everything will be clogged with dust."
"I've a better idea," someone interjected. "Drive a pipe down through the roof."
"You'll need two pipes," pointed out another speaker. "One to pump in oxygen, the other to suck out the foul air."
"That means using a complete air purifier. And we won't even need it if we can get those people out inside the ninety hours."
"Too big a gamble. Once