Mapping the Moon

Second of the week's big shots sent a smaller bird aloft, but the flight of the Ranger VIII moon probe was an even greater achievement. After a 66-hour, 234,300-mile trip, the spacecraft's six cameras panned across the luminous lunar surface taking thousands of snapshots of the great craters and dusty plains that U.S. astronauts hope to explore. Before the automated voyager crashed within 15 miles of its preselected impact point, the exquisite accuracy of all its maneuvers testified to the growing skill of U.S. spacemen.

Hitting the moon at all with a man-made missile is a prodigy of calculation and performance, and Ranger's builders have learned to turn the trick only after profiting from the experience of heartbreaking failures. Their first five shots fizzled. The sixth was on target, but its TV cameras failed to function. Ranger VII did everything right; its radioed photographs may have told little to amateurs, but they made professionals more familiar than ever with the planet they plan to visit. Then came Ranger VIII, and man got his clearest look yet at his closest planetary neighbor.

Correct Correction. The first step toward a precision Ranger shot is to put the spacecraft on a parking orbit around the earth. That orbit is then analyzed by computers; the spacecraft's altitude, speed and direction must be measured with infinite care, for the next burst of power must boost the spacecraft through an imaginary target 120 miles above the earth and only ten miles in diameter. Only then can a mid-course correction of trajectory put the spacecraft inside the selected area.

Ranger VIII hit the ten-mile target at the correct speed, set itself at the proper angle to the sun and the earth, and kept in tight communication with its ground-control stations. About 17 hours after launch, the command came from its masters at Pasadena's Jet Propulsion Laboratory to prepare for the critical mid-course maneuver. Dutifully Ranger writhed in space, turning its gleaming golden body as it was told. It fired its small rocket engine for 59 seconds, and when it had writhed back again to cruising attitude, JPL scientists predicted that it would hit inside an "ellipse of probability" 40 miles wide and 75 miles long in the southwest corner of the Sea of Tranquillity. "Those trajectory guys are getting good," said a JPL spokesman. "It looks as if Ranger VIII will be even more accurate than Ranger VII."

The Sea of Tranquillity was the target picked before the launch. Ranger VII had photographed a fairly smooth-looking place now called the Mare Cognitum (Known Sea) and found it to be pocked with small pits apparently made by chunks of rock tossed out of the crater Copernicus. A lunar landing vehicle might have serious trouble with such pits, and the hope was that the Sea of Tranquillity would prove to be smoother.

Ambitious Voyage. For 50 hours, Ranger VIII cruised through space, its speed gradually slowing under the backward pull of the earth's gravitation. Then it felt the forward pull of the moon's gravitation and began to gain speed. As the spacecraft curved into its final dive, it swept across the face of the moon at a lower altitude than its predecessor. In 23 minutes it sent back 7,000 pictures, nearly twice the number returned by Ranger VII, over a five-minute longer span.

The first pictures covered a rectangular area 200 miles wide and 400 miles long. In the final second before Ranger collided with the onrushing moon its cameras were snapping closeups of moon segments no larger than a city block. Even so, after scanning the lunar snapshots, scientists were still undecided whether the moon's surface would support a spacecraft. A "personal guess" by Dr. Gerard Kuiper, head of the scientific team analyzing the evidence, was that the moon is coated with a frothy substance that "may hide many treacherous things." The University of California's Dr. Harold Urey argued on the other hand that photographs of several craters showed "a whitish button on the bot tom," suggesting that there is "very hard material underneath."

The final verdict will not be in until the scientists have analyzed their bountiful crop of pictures. Meanwhile, there will be still more unmanned shots at the moon. Man's most intricate machines will peer at the moon from all angles, prod its surface and map its contours with cautious patience before man himself essays that ambitious voyage across space.

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