One for the Scientists

NASA's $350 million Surveyor program has already tested the bearing strength of the lunar surface and scouted all the proposed flatland target sites for the U.S.'s first manned moon mission. This was accomplished spectacularly in four out of six shots; Surveyor's budget authorized seven. What to do with the last moon robot? As a sort of job-end bonus for a mission brilliantly accomplished, NASA left it up to a panel of lunar experts. They decided to gamble on an exploratory shot to one of the moon's unknown upland regions: the rock-strewn ridges just north of the crater Tycho, in the moon's southwestern quadrant.

Even with luck, mission controllers at Pasadena's Jet Propulsion Laboratory gave themselves only a 40% chance of a successful landing. If one of Surveyor 7's three feet landed on a high rock, the craft would tip over, rendering its cameras and testing equipment useless. Or the feet might straddle a rock, which would then smash into the spacecraft's delicate underbelly. In an almost shoot-the-works mood, therefore, Surveyor 7's controllers fired the retrorockets at the end of the 66-hour, 225,000-mile journey last week. The craft obediently braked from 6,000 m.p.h. to less than 7 m.p.h., fell freely for the final 13 feet, narrowly missed a field of jagged boulders and landed two miles from its designated bull's-eye. Back in Pasadena, there were cheers and handshakes all around.

Jewel-Box Glitch. Tycho's significance lies in the fact that it is one of the moon's youngest and major craters. From its 15,000-foot depths, a pattern of grooves or ridges spokes out over hundreds of miles of the moon's pock-marked surface. The scientists hoped to compare the composition of this terrain with that of the low-lying basically basaltic equatorial "seas," studied by earlier Surveyors. Since Tycho is believed to have been formed by the impact of a giant meteorite, and by the intense volcanic activity that followed, a look at ejected material surrounding the crater might provide the best clues yet to the internal composition and geological history of the moon.

To do the job, the plan was to lower a "golden jewel box" to the moon's surface, dig an 18-inch hole with the spacecraft's mechanical arm and claw, then use the arm to put the jewel box in the hole. By bombarding the claw-dug moon material with alpha particles and measuring the speed and number of the rebounding particles, the 8-in.-sq. box could identify the chemical composition of substances beneath the moon's surface. Contamination by material from other parts of the moon and from meteorites would be avoided.

The plan ran afoul of Surveyor 7's first glitch. After firing a small explosive charge to free the box, the scientists began lowering it on a nylon cord. Halfway down, the box stuck. Using the spacecraft's TV camera to hunt for the source of the trouble and working with duplicate models, JPL scientists and engineers from JPL and Hughes Aircraft, designer of the moon robot, struggled to set it free. Twice they nudged it with the digger arm. No luck. All it did was swing a bit. Then they tried again, using the arm to steady the box against Surveyor and simultaneously pressing down. This time, success. The box descended to the lunar surface, and the crucial, drawn-out process of testing began. This week JPL will be sifting the first results relayed to earth from the box.

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