Lunar Blindness

If the Russians know why their space ship Luna 7 cracked up in its effort to make a soft landing on the moon last month, they are not telling. But Dr.

Anthony Barringer, a Canadian geophysicist, is unbothered by Soviet se crecy. At a symposium on remote sensing in Huntsville, Ala., last week, he theorized that Luna 7's radar may have failed to "see" a top porous layer of the moon's crust. As a result, the space ship crashed on its way to a landing on the hard lunar rock below.

When he heard that Luna 7 had successfully fired its braking retrorockets and had transmitted signals for three seconds after hitting the moon, Barringer became convinced that the craft was not demolished upon impact. The tardy retrorocket firing that probably made the difference between success and failure, Barringer decided, could have been caused by an altimeter error of as little as 30 ft. -- which some scientists believe is the approximate depth of a layer of porous rock or partially compacted dust that covers the moon. Barringer's conclusion: Russian radar penetrated the moon's top layer, reflected back from the bedrock below and reported an incorrect altitude.

Sophisticated Conjecture. Such lunar theorizing is based largely on earthly experience. Barringer has already designed effective radar systems to measure the thickness of antarctic ice, which is largely transparent to many low-frequency radars and radio altimeters, a phenomenon that results in incorrect altitude readings and has caused several plane crashes. Barringer is also conducting laboratory experiments for NASA to study the possibility of designing a radar system that would measure the thickness of the moon's surface layer from an orbiting vehicle. He has bounced radar pulses off simulated lunar crusts made of porous lava and compressed lava dust, and found that both are highly radar transparent.

Scientists at both NASA and Caltech's Jet Propulsion Laboratory, which is building Surveyor, the first U.S. lunar soft-landing vehicle, remain skeptical of Barringer's theory. They say it is still largely conjecture. But it is conjecture that has made the problems of radar transparency a vital concern in the design of a sophisticated Surveyor altimeter that should have no trouble distinguishing the true surface of the moon.

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