Toward the Moon

Precision was hardly a precise enough word to describe what would be required of the rocketing spacecraft Ranger 6 as it reached for the moon. To begin with, said the Jet Propulsion Laboratory men who sent it on its way, Ranger would have to hit the imaginary opening at the lower end of an imaginary pipe curving through space--a ten-mile circle 115 miles above the earth. Only if it scored a bull's-eye at just the right orbital speed would Ranger have a chance of getting where it was supposed to go. And even then it would have a whole succession of difficult tricks to perform before it arrived on the proper part of the moon's surface.

Nestled in the nose of a two-stage Atlas-Agena rocket, the spidery, gold and silvery Ranger took off from Cape Kennedy and arced neatly into a perfect orbit. When it had coasted for 19.5 minutes, the Agena second-stage rocket fired again, pushing it right through the end of the imaginary pipe. On the ground, giant antennas followed its course, measured its speed. Computers analyzed the data furiously. JPL announced confidently that Ranger 6 was on a course that would miss the moon by only a piddling 600 miles. The error was comfortably within Ranger's powers of mid-course self-correction.

On Course. The spacecraft's 15-ft. wings, studded with solar cells, were open now, and freshly generated electricity was coursing through its metallic arteries. Ranger had rolled and pitched correctly by spurting tiny jets of gas, and its sensors were locked on the sun and the earth. Its dish-shaped high-gain antenna had craned its neck and pointed toward the earth; a stream of coded information was throbbing along its narrow radio beam.

But the spacecraft still had much to do before it could focus its close-up TV cameras on the hostile surface of the moon. JPL's tracking antenna at Goldstone in the Mojave Desert followed Ranger through space, collecting radioed reports about the functions of its intricate apparatus. All seemed to be going well, but JPL engineers had to wait anxiously until Ranger 6 had cruised for 17 hours and was nearly halfway to the moon. Then they sent a signal that put the spacecraft into a flurry of activity. Its little gas jets spurted measured amounts of thrust, making its axis turn in the exact direction computed at faraway Goldstone. Its directional antenna turned prudently to one side to get out of the hot blast of the course-correction rocket.

Impact on Tranquillity. Reports came back to Goldstone over the nondirectional antenna that all this had been done. Then, on signal, the hydrazine-burning correction rocket fired for 69 seconds, increasing Ranger's speed by 92 m.p.h., putting it on a trajectory designed to hit the slant-lit center of the waning moon. The spacecraft then returned to its cruise position, with its sensors locked to earth and sun and its directional antenna aiming its beam at the earth. Just 13 hours after the midcourse maneuver, JPL announced that Ranger 6 would hit the Sea of Tranquillity on the moon.

Slowed by earth's gravitation and not yet accelerated by the pull of the moon, the spacecraft would have to cruise for hours more, exposed to all the known and unknown hazards of space. One hour before impact, according to the plan, when it is about 4,000 miles from the moon, Goldstone would tell it to turn again, pointing its six TV cameras at the approaching lunar surface. With the moon 900 miles away and Ranger approaching at 4,000 m.p.h., the six cameras would start taking pictures--more than five per second. Radioed back to earth, those pictures would have helped pick a site for future manned moon landings. But in its final dive, Ranger 6 made its first failure. Its TV cameras did not warm up to full power and no pictures came back to earth. Goldstone scientists could console themselves that they had made a remarkably accurate shot--and that they had three Rangers left to give them their longed-for look at the moon.

This file is automatically generated by a robot program, so reader's discretion is required.