Venus Observed

Some time in mid-December, if all goes well, the spacecraft Mariner II will skim within a scant 10,000 miles of Venus. Like a great mechanical bug, it will point its electronic eyes at the cloud-covered planet; and then, after a brief, 30-minute look, it will soar past to lose itself in orbit around the sun. But before it cruises beyond radio range of earth. Mariner should report back to its human creators and tell them more than man has ever known before about his planetary neighbor, the heavenly body that most resembles earth in orbit, size and mass.

Mariner is only a distant relative to the manned Mercury capsules and the Russian Vostoks that have already orbited the earth. It is a remote-controlled robot, and it is traveling toward the far reaches of space--far beyond man's still limited reach. But it is carrying the most sophisticated scientific cargo yet sent aloft. Its complex instrumentation is a U.S. triumph.

Merely getting Mariner aloft was a frustrating task. Last month Mariner I was blown up by a range safety officer when it wandered erratically off course.

Last week, on Cape Canaveral's Launch Pad No. 12, Mariner II also seemed doomed. The countdown was halted three times to allow technicians to examine malfunctions. When the spacecraft finally rose above its flaming tail and disappeared into the warm darkness, preliminary tracking data from Johannesburg indicated that Mariner might miss Venus by some 600,000 mile's--too large an error to be corrected by its mid-course steering motor.

But it was Johannesburg, not Mariner, that had made the big mistake. The start of the flight had been almost perfect. The Atlas booster shoved the spacecraft up to a height of 112 miles before its engines cut off and it separated from the rest of the vehicle as planned. Next, the second-stage Agena B rocket fired Mariner II into an 18,000-m.p.h. "parking" orbit. Cutting off its engine, Agena B then coasted until it reached the precise point for another firing, which nudged Mariner II toward outer space at an earth-escape velocity of 25,526 m.p.h.* Command to Jets. Mariner II was now under radio command from California Institute of Technology's Jet Propulsion Laboratory. The first order was received and obeyed: large, flat solar panels (see diagram) sprang into position. In a series of maneuvers, Mariner's ten tiny nitrogen jets swiveled the spacecraft until its long axis pointed at the sun. So positioned, the solar panels could absorb the sun's energy, power the spacecraft's electrical system without draining its silver-zinc battery.

After seven days, Mariner will be given another command. Its high-gain directional antenna, needed for radio transmissions over the millions of miles that will soon separate Mariner from earth, will be ordered to focus on the earth. Then, if all goes well, Mariner will be stabilized on two axes--one pointing at the sun, the other at the earth.

With Mariner so oriented, scientists will be able to order its steering rocket to make speed and directional changes in midcourse. Such changes will probably be necessary some time this week, because tracking data indicate that Mariner will pass some 250,000 miles from Venus instead of the 10,000 miles required for scientific experiments--an error that is well within Mariner's power of correction.

Pass at Venus. Shooting a space vehicle so close to Venus is vaguely comparable to trying to shoot a bird on the wing from a speeding boat. Both Venus and Earth are racing on orbits around the sun.

Manner, in order to make a pass at Venus, must travel more than 180 million miles in a curving trajectory (see diagram), even though Earth and Venus are only 69 million miles apart at time of launch.

Not until Dec. 13 or 14 will Mariner pass close to Venus. But along the way it will conduct four experiments that are expected to tell scientists much about the conditions in interplanetary space. A magnetometer in the 447-lb. spacecraft will measure the magnetic fields of space and Venus. An ionization chamber and a group of three Geiger-Miiller tubes will measure the number and intensity of such high-energy particles as protons, electrons and the nuclei of atoms, in an effort to gather more knowledge about the hazards of manned space flights. One instrument will determine the flow and density of the charged particles (the solar wind) that are constantly streaming outward from the sun. Another will detect cosmic dust that might prove dangerous for future astronauts traveling through interstellar space.

An End to Argument. But the major purpose of Mariner II is to settle some old scientific arguments. Although Venus is Earth's nearest planetary neighbor, scientists have been able to learn very little about it. Venus is covered with a dense layer of clouds that hides its surface. Scientists have variously estimated its temperatures from 38DEG below zero in its upper atmosphere to 615DEGF. near its surface.

Some have theorized that the planet is nothing but a baked desert; others that it is covered with oceans. Still others have concluded that Venus' atmosphere is mostly carbon dioxide and nitrogen; they argue that there is neither enough water nor enough oxygen there to support life.

When Mariner comes close to Venus, a radiometer will scan the planet's surface to detect the microwave emissions that would indicate the presence of water in the atmosphere and the temperature at the planet's surface. In a companion experiment, an infra-red radiometer will also scan Venus to get readings on temperature and atmospheric conditions.

From Mariner's radioed reports, scientists hope to put together information that will help them decide about the possibility of Venusian life. But even if they decide that Venus is a lifeless lump in space, Mariner II may still provide the basic data that will some day help man to plan his first voyage to the nearest planet.

* Soviet scientists had attempted a similar feat two days earlier, failed. Last week tracking stations picked up three of the Russian rocket components orbiting the earth; the fourth burned up in the atmosphere. The previous Soviet Venus probe in 1961 suffered a radio communications blackout after 18 days.

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