The yellow gauge clicked with a tiny sound, and the oxygen tank went dry. The relay ratchetted slowly, automatically coupled on the next tank, and the needle on the gauge climbed to high-pressure again. Bart Caxton watched the needle swing, and beads of perspiration rode high on his cheekbones. He twisted the metal mug in his hands, and his voice was ragged with welling emotion. "Three weeks," he said viciously. "And we're five weeks from the shipping lanes. There isn't enough oxygen to carry us