The Disobedient Rocket

One fine afternoon a huge Atlas rocket took off from Cape Canaveral carrying an Agena B as its second stage. On the nose of the Agena perched Ranger III, a 727-lb., $7,000,000 marvel of precision and ingenuity that U.S. spacemen hoped last week would send back closeup TV pictures of the moon, and land a small, tough seismograph on the lunar surface.

Ranger I and Ranger II had been flops because of bad propulsion; Ranger III's launch was apparently O.K. The Atlas fired its three motors, then plopped back into the ocean as planned. The Agena fired and soared into a "parking orbit," circling 105 miles above the earth. At the proper point on this orbit, Agena fired again to sling itself into a collision course with the moon. Ranger IIIs radio went on the air, and its reports were favorable.

Then from radio monitor stations strung around the girth of the earth came bad news. One of the rockets had given too much push, and Ranger III was moving too fast. Instead of streaking toward the moon at the proper speed of 24,500 m.p.h., it was moving at more than 25,000 m.p.h. It would slice through the moon's orbit in 55 hours instead of 66 as planned. And at that time, the moon would not be there; Ranger III would miss by nearly 25,000 miles (see diagram).

Locked on the Sun. But the shot was not a total flop. Ranger III was as crammed with electronic tricks as a barrel of transistor radios. Even though its launching had been faulty, it was cruising undamaged through space, its intricate apparatus still in working condition. Just 27 minutes after launch, Ranger's C.C. & S. (Central Computer and Sequencer) began issuing commands that had been stored in its electronic brain. Explosive pin-pullers released solar battery panels, which unfolded like the wings of a butterfly. At the same time, Ranger's dish-shaped, long distance radio antenna swung out into position. A few minutes later the C.C. & S. commanded six light sensors to find the direction of the sun. Then an attitude control system of gyros and small nitrogen gas jets went into action, turning Ranger III until it locked on the still-distant sun, its broad butterfly wings absorbing maximum power from the sunlight. Some three hours later, C.C. & S. started another series of actions that turned the Ranger's rotatable dish antenna toward the receding earth. Radio signals reported success loudly and clearly over the antenna's strong, narrow beam.

There was no chance that Ranger could hit the moon, but it could curve its course closer to its target. Happily, its C.C. & S. could listen as well as command. Half a day after launch, when Ranger III was nearly 100,000 miles away from the earth, scientists from Pasadena's Jet Propulsion Laboratory, where Ranger had been built, began sending new orders that C.C. & S. acknowledged and "memorized." After the command to "execute" went out, Ranger III started a complicated series of maneuvers. Its little gas jets turned it to a new attitude. Then its large midcourse rocket motor burned hydrazine for a specified number of seconds. After the motor shut off, Ranger III locked itself to the sun again and turned its dish antenna toward the earth. Finally it reported, detail by detail, that it had obeyed its orders. But the last-minute midcourse correction was too small. Because of its errant launch, Ranger III still could not score a bull's-eye.

Find the Moon. Next day another series of commands streamed out across space. C.C. & S. listened, acknowledged and memorized. When the "execute" command came, Ranger turned the lens of its TV camera toward the approaching moon. The lid that protected the lens from micrometeorites was swung away; the camera was turned on and given 30 minutes to warm up. At another memorized command from C.C. & S., it started shooting video pictures of the moon about 30,000 miles away. At this point Ranger III made its first error: it did not hold its dish antenna pointed steadily at the earth; the pictures that it sent to earth were an almost meaningless blur, no use at all to the stay-at-home scientists.

By week's end, Ranger III had swept far past the moon, missing its moving target by 22,862 miles. Now it is in orbit around the sun. J.P.L. scientists have two more Rangers nearly built--and they can now be sure that a good launch is all that stands between them and the moon.

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