1958 Alpha

Even while on its Florida launching pad, the Army's satellite Explorer (official scientific name: 1958 Alpha) insistently broadcast its hoarse radio cry. Ten minutes after takeoff, Antigua in the British West Indies heard it soar triumphantly overhead. Fifteen minutes later it was radio-tracked over Ghana on the west coast of Africa. Around the earth it swept, but not until it passed homebound over California--nearly two hours after it left the ground--were the scientists sure that their bird was in a stable orbit.

The launching vehicle that put it there was a special, four-stage version of the Army's test rocket, the Jupiter-C. Its first stage, which contributed most of the push into space, was the familiar, well-tested Redstone, fitted for the occasion with slightly longer fuel tanks, and burning a hydrazine-based, exotic fuel called Hydyne, which gave more thrust than its motor's usual diet of alcohol. Stuck on its nose was an awkward-looking, cylindrical "bucket" mounted on a bearing so that it could be spun, and containing a cluster of 14 small, solid-fuel rockets, 40 in. long and 6 in. in diameter. Atop the bucket was a single, 80-in., solid-fuel rocket with the satellite proper forming its forward part.

As firing time approached, the bucket, driven by a small electric motor, began to rotate. This motion had the same purpose as the spin of a rifle bullet: to "spin-stabilize" the upper stages of the rocket. It would also check any tendency to veer off course if any of the small rockets in the bucket should ignite later than the others, or burn erratically.

Bird at Peak. When ready for firing, the whole assembly weighed 65,000 lbs., so the 83,000-lb. thrust of the first-stage rocket motor lifted it off the ground at a fairly fast clip. The first stage burned for 150 seconds. When its fuel was gone, about 60 miles above the earth, most of the Redstone dropped away, leaving only a short section of the nose attached to the spinning bucket. As it zoomed upward at several thousand miles per hour, a gyroscopically controlled device turned the missile's attitude toward the horizontal by blowing jets of compressed air through nozzles. This process took about 240 seconds. By that time the bird was at the peak of its first-stage flight, and pointing in the direction of its intended orbit.

All the while, it was being tracked from the ground in four different electronic ways, and Dr. Ernst Stuhlinger, German-born rocket expert, was waiting for a complicated instrumental setup to tell him the exact time to ignite the second stage and "inject" the satellite into its orbit. When the shortened assembly reached about 200 miles altitude and was pointing in the right direction, he pressed a button.

Obeying his electronic command, eleven of the small rockets in the bucket fired, blasting away the nose of the Redstone. They burned for six seconds. Two seconds after that, three more rockets fired, pushing free the empty shells of the first eleven. The central rocket carrying the satellite fired last. It spurted ahead and alone, and reached orbital velocity of more than 18,000 m.p.h.

That was it. Everything worked perfectly without the slightest hitch, and the first U.S. satellite was in orbit.

Southerly Swing. Unlike the Russian Sputniks, which sweep close to the Arctic and Antarctic Circles, the Explorer follows a sinuous orbit around the earth's middle, crossing the equator at an angle of about 34DEG and coming only as far north as Atlanta. At its highest point (apogee), the orbit rises to 1,700 miles above the earth, descending to about 200 miles (perigee). The round trip takes 114 minutes. This is a "safe" orbit, above nearly all the drag of the atmosphere, and higher than the orbits of the Russian satellites.

None of the scientists wants to predict how long the Explorer will cling to space, but Major General John B. Medaris, head of the Army Ballistic Missile Agency, thinks it may stay up for as long as ten years.

Dr. William H. Pickering, director of the Army's Jet Propulsion Laboratory in Pasadena, which developed the upper stages of the launching vehicle, says that the orbit is almost exactly the intended one. The only deviation is that the satellite goes a little higher than was expected. "A splendid orbit," says Dr. James Van Allen of the University of Iowa, who designed the instrument package for the satellite. "We are delighted with it." He points out that the principal scientific purpose of the Explorer is to study cosmic rays at various distances from the earth, and it could not do this so well if its orbit were more nearly circular.

The chances are that only people with very good eyesight, who live in favorable places, will ever see the Explorer with the naked eye. It is too small. In any case, says Dr. Fred Whipple, head of the Smithsonian Astrophysical Observatory at Cambridge, it will only be visible while its elliptical orbit is carrying it over the U.S. at low altitude. When the high part of the orbit has shifted over the U.S. the satellite will be too faint to be seen without instruments.

Those who do see it as a faint, speeding star will notice that it does not wax and wane like the conspicuous rocket that accompanied Sputnik I. This is because its spin stabilization keeps it from tumbling. Its direction, like that of a free gyroscope, is fixed in space. As it rounds the earth, its axis points at the same distant star.

Sophisticated Instruments. The orbiting body, including the burned-out rocket, is 80 in. long, 6 in. in diameter, and weighs 30.8 lbs. The satellite proper weighs 18.13 lbs.; of this, its steel outer skin weighs 7.5 lbs., and the rest, nearly 11 lbs., is the payload of instruments. These weights do not compare with Sputnik I (184 lbs. without its rocket) or Sputnik II (1,120 lbs. with dog and rocket), but the Explorer's instruments are so light and sophisticated that they may send as much information from space as their Russian rivals.

The "Van Allen package" of instruments assembled by the Jet Propulsion Laboratory is designed to measure three things: cosmic rays, micrometeorites, and the temperature of the satellite itself. The cosmic-ray counter is a Geiger-Mueller tube that gives a signal whenever 32 rays have passed through it. It began performing normally as soon as the bird was launched.

Micrometeorites, the tiny specks of high-velocity dust that infest space, are detected in two ways. A delicate microphone listens for vibrations set up in the satellite's steel skin when it is hit by a micrometeorite. The strength of the vibration is a measure of the impact. The other detector, on the outside of the satellite, is a set of twelve grids, wound with extremely fine wire. When one of the wires is hit by a particle more than 5 microms (one five-thousandth of an inch) in diameter, it will break and tell about the damage. This set of instruments was designed and supplied by the Air Force Cambridge Research Center.

Sensing devices (small, highbrow thermometers) take the temperature of the satellite at four places as it orbits in and out of the cold shadow of the earth and the blazing glare of the sun. Two of them are in the skin, fore and aft. One is in the instrument section, and the fourth is inside the nose cone. The reports from the four sensing devices will help design space vehicles that men can live in without too much temperature trouble.

Information from the instruments is sent to earth over two tiny radio transmitters, which weigh 2 lbs. each with their batteries. The more powerful one, which radiates sixty-thousandths of a watt on 108.03 megacycles, is expected to stay on the air for two to three weeks. The low-power transmitter (twenty-thousandths of a watt on 108 megacycles) draws less current, so it will probably broadcast for two or three months.

Microlock. This is feeble power indeed, but the signals, which are not Sputnik-style beep-beeps but continuous tones only slightly modulated, have been picked up widely by radio amateurs as well as by the official satellite tracking stations. Instructions on how to receive them and how to interpret the information that they carry were given freely in advance to all interested parties. The U.S. satellite, unlike the Soviet Sputniks, will talk to all the world.

The frequency of the signals is rather high for most radio hams, but it was picked because it can give more accurate data on the satellite's position than the Sputnik frequencies on the 20-and 40-megacycle bands. Special "Microlock" detecting stations designed by the Jet Propulsion Lab have been set up at the Florida launching site and Earthquake Valley near San Diego. Two more, operated by the British, are at Ibadan in Nigeria and at Singapore.

Since the Explorer moves at 18,000 m.p.h. or better, the Doppler effect makes the frequency of its signals change considerably as it approaches and recedes: when it is approaching a listening point, its frequency is higher; when it is moving away, its frequency is lower. The new Microlock receivers freeze to the signal, measure the shift of its frequency, and use it to estimate the satellite's speed. Their wide directional antennas pinpoint its position. After this system has been in operation for a while, the Explorer's orbit should be known more accurately than the Russians know the orbits of their now-silent Sputniks.

If the Explorer stays up as long as expected, the slow shift of its orbit will give information about irregularities in the earth's gravitational field. Its radio signals, coming down through the atmosphere, by their fading and bending will describe ionized layers of air they have passed through. As the satellite spirals toward earth, very slowly at first, it will measure by its loss of energy the density of the air at the top of the atmosphere. It may even tell, merely by crossing the oceans at a known speed, how far the continents really are from each other--a question that still defies the more meticulous mapmakers. If the measurements are accurate enough, i.e., down to the last foot, it may answer in time the old geological argument about whether North America and Europe are slowly drifting apart. It would also give more accurate firing data to intercontinental ballistic missilemen.

Tomorrow the Moon. Perhaps the most remarkable thing about the Army's satellite is that its success was not due to new or startling equipment. The Redstone, which has long been in production, is essentially an improved German V2. The Jupiter-C version, with its spinning bucket of small rockets, is not new, either. Neither are its internal guidance instruments, its attitude-control device or its tracking systems. Nearly everything except the satellite itself and perhaps the rocket attached to it was "off the shelf."

According to Dr. Wernher von Braun, the same equipment plus a few more tricks can put 50% more weight on orbit. But he and other Army men point out that the Redstone is a comparatively small rocket, not nearly so powerful as the ones that launched the Russian Sputniks, or as military rockets--Atlas, Thor, etc.--now being tested in the U.S. Dr. Jack E. Froelich of the Jet Propulsion Laboratory says that the Army's Jupiter rocket (not to be confused with the Jupiter-C) could boost a much bigger satellite into an orbit, or even send it around the moon.

Projects of this sort are apparently in the works. A spokesman for the Army announced plans for a 500-lb. space vehicle that can be used for military reconnaissance, presumably taking pictures of the terrain that it passes over and sending them back to earth by radio or TV. Another announced Army project is a rocket motor with 1,000,000 lbs. of thrust, twelve times the power of the souped-up Redstone. Meanwhile, said Dr. von Braun, a second Jupiter-C is being made into a satellite launcher. Some time between now and April it will toss another small satellite, probably equipped with different instruments, into its round-the-world orbit.

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