Back from Space

It was the autumn of 1954, and the U.S. was hard-crashing a life-or-death program: the development of a rocket that could bellow into space, span oceans and continents, plunge down through the atmosphere and deliver an H-bomb payload anywhere on the earth.

The difficulties were staggering. Every aspect of the project called for prodigies of technology. But the most formidable problem of all was one that should have been familiar to anyone who ever saw a meteor turn into a trail of fire in the night sky. It was the problem of "re-entry": how to get an ICBM warhead, with its protective nose cone, back through the earth's atmosphere without its being burned into sky-streaking embers. As history may one day note, it was at an Ithaca, N.Y. cocktail party that one of the most significant early steps toward success was taken.

The Someone. Among the guests at that party was a trustee of Ithaca's Cornell University named Victor Emanuel. Emanuel was also board chairman of Avco Corp., which was already deeply interested in the U.S. ICBM program. He fell into conversation about the project's difficulties--particularly that of testing re-entry techniques in earthly laboratories. Said one of the group, pointing to a heavy-shouldered man: "I believe we have someone right here who can help you."

The someone was Dr. Arthur Kantrowitz, a Cornell professor of aeronautical engineering. Within minutes, Emanuel and Kantrowitz were deep in conversation. Soon Kantrowitz was heading up a staff at Avco's newly established research laboratory at Everett, Mass.

What Kantrowitz, who perhaps more than anyone else rates the title of "Mr. Nose Cone," had to offer was experience and expertness in a testing device known as the shock tube. The problems of nose-cone re-entry were fearsome enough on paper. It was understood all too well that an ICBM re-entry body of cone and warhead would have to crash back into the earth's atmosphere at near-meteor speed of 15,000 m.p.h., with enough motion of energy to vaporize five times its weight of iron. Piling up ahead of the re-entry body would be a high-pressure air layer reaching up to 15,000DEG F.--about 1 1/2 times as hot as the sun's surface. But beyond that, the physical properties of air at such speeds and temperatures were almost entirely unknown, and no existing wind tunnel was fast enough to furnish the necessary data. Kantrowitz' shock tube supplied crucial answers.

The Violent Instrument. Essentially, a shock tube is a strong-walled metal pipe, a few inches in diameter, from which the air can be pumped. At one end, a section is walled off by a copper diaphragm: that section is filled with an explosive mixture of oxygen and hydrogen. At the other end is a vacuum tank, and just ahead of it is a tiny nose-cone test model. When an electric spark explodes the oxygen-hydrogen, it bursts through the diaphragm and into the vacuum. Ahead of it rushes a hot shock wave that hits the test model at actual re-entry speed and temperature. The flow lasts no more than one-thousandth of a second, but it is enough to yield volumes of scientific information. After only six months of work with this violent instrument. Kantrowitz was able to send the Air Force the first firm data about heat and air conditions around a nose cone at its moment of crisis.

From that point on, real progress could be made, and both Avco and its respected competitor. General Electric Co., went to work along paths that at times diverged and at times converged.

Snub Nose. The easiest, fastest cone to develop was the "heat-sink"' type, made of thick copper. Since copper is an excellent conductor of heat, the cone's front surface could stay solid until the whole mass was near the melting point. To many, it seemed obvious that a nose cone should be made slim and sharp-pointed, capable of piercing the atmosphere with low resistance. But the contrary proved to be the case. Dr. H. Julian Allen of the National Advisory Committee for Aeronautics argued conclusively that a blunt nose was better for the heat-sink cone. The snub nose, said Allen, would help pile up in front of the cone a high-pressure layer of air that would itself act as a potent insulator. That way, most of the immense heat would be swept off the edge of the cone into a long tunnel of air.

Along such relatively simple lines. General Electric built most of the early nose cones and, considering the state of the art, they were successful enough in the first Thor and Atlas missiles. But they were heavy--and in an ICBM, every ounce of nose cone takes away from the warhead which is the rocket's real reason for being. And the blunt-nosed cones began slowing down while still high in the atmosphere, making them more vulnerable to antimissile missiles as they descended toward earth.

Flaming Arc. Thus, even while the heat-sink cones were still being tested, both G.E. and Avco started work on a new kind of cone. It was deliberately designed so that some of its material would be "ablated"--vaporized and blown away into nothingness by the intensely hot air through which it raced. Ablating cones promised a weight advantage, but not even the shock tube was adequate to test them at the research level. Therefore a new testing device, the arc wind tunnel, was tailored for the job.

In the arc wind tunnel, air is first pumped out of a big vacuum chamber. Then a valve is opened and new air rushes in. On its way, it passes through a flaming arc using kilowatts enough to light a city. The air's temperature soars to 14,000DEG F., and it whams into samples of ablating material that behave as if they were part of a real nose cone.

The ablating nose cone is the design of the present. It is longer and more pointed than its heat-sink predecessor. It can slice more deeply through the atmosphere before it slows down, giving it greater protection against defensive missiles fired from the ground. Better still, it is comparatively light: the G.E. ablating nose cone used on the "longfellow'' Atlas fired May 20 from Florida to the Indian Ocean probably played an important part in the missile's being light enough to attain its 9,000-mile range.

Point of Light. Much work remains to be done. Nose cones can be made still lighter, thus adding to the missile's payload. This is particularly important to the solid-fuel, second-generation Minuteman, a fine but small missile with definite payload limitations. Already in the works are plans to make re-entry bodies maneuver so that their courses will be unpredictable and hard to intercept. To do this, the re-entering bodies must have controls and some sort of wings to give them lift, or to make them plunge steeply, or to let them dodge from side to side.

Also in the visible future is the manned spacecraft that, with techniques based on military nose-cone research, will bring its human travelers safely down from orbit or from an interplanetary journey. Strangely, the manned spacecraft in some ways presents fewer problems than the ICBM. Where an ICBM enters the atmosphere at about a 20DEG angle with a sudden, explosive shock, a space vehicle can come into the atmosphere flat, keeping its deceleration and temperature comparatively low.

The future is filled with exciting problems. But the present is reality. On many a night, the inhabitants of Ascension Island in the South Atlantic can see a point of light darting through the heavens. It hurtles closer and grows bigger than any star or planet before crashing into the sea 100 miles away. It is another U.S. missile, fired from far-away Florida, that has soared 600 miles into space and successfully returned through the atmosphere. It means that the basic re-entry problem has been licked.

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