More from the Moon

As they struggle to get the U.S. moon program back on schedule, scientists are anxiously seeking the cause of Apollo 13's brush with disaster. At the same time, they are still analyzing the findings of earlier lunar missions. Both efforts are paying off handsomely:

> After six weeks of investigation, NASA's high-level review board proposed an explanation for the explosion of Apollo 13's oxygen tank. The blast was apparently caused by the failure of two thumbnail-sized automatic switches that are designed to shut off the oxygen tank's internal heater if its temperature rises above 80DEG F. Tests showed that the temperature, if unchecked, could soar as high as 1,000DEG and cause the electrical insulating material to flake off. The arcing that results can ignite the insulation. Heat from the fire expands the compressed semiliquid oxygen, and its pressure eventually increases enough to burst the tank. The safety switches were apparently damaged when the heater was used during a test before the launch.

> The small, lemon-sized rock from the Ocean of Storms resembled an ordinary piece of granite, but it was, in fact, unlike any earthly specimen--or any of the other lunar material brought back by Apollo 12. It contained 20 times as much radioactive uranium, thorium and potassium as comparable amounts of other moon material and was the oldest lunar specimen yet obtained. Radioactive dating tests made by Caltech Geologist Gerald Wasserburg indicated that the rock was formed 4.6 billion years ago--around the time that the moon and the planets arc believed to have been created. Scientists hope that further examination of the rock will provide new insight into the formation of the solar system.

> As Apollo 11 sped back to earth last July, Astronaut Buzz Aldrin kept seeing strange flashes of light in the darkened spacecraft, even though his eyes were closed. "I think I'm going out of my mind," Aldrin told Neil Armstrong. While Armstrong and other astronauts confirmed the mysterious flashes, NASA scientists were at first inclined to attribute them to an optical quirk. Now they have proposed a more plausible explanation: cosmic rays. Though only some of these high-speed particles--mostly protons--manage to break through the shield of the earth's magnetic field, they can easily penetrate the eyelids of a space traveler, pass through the eye fluid and strike the retina. At times, they may even hit the brain's optic nerve. Such bombardment causes no serious damage during a short lunar mission. But since the effect of cosmic rays on the body is cumulative--like that of X rays--they could present a greater peril on prolonged space voyages.

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