Tracking the Man-Made Satellite
July 1957 Radio & TV News

July 1957 Radio & TV News [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged.

Here is a great look inside the planning and operation of the "Minitrack" systems used for Project Vanguard to track the Sputnik, Echo, Explorer, and other early Earth artificial satellites during the International Geophysical Year (IGY) activities. From a 1957 issue of Radio & TV News magazine: "Essentially, the [IBM 704's] storage function works by means of doughnut-shaped cores, about the size of pinheads, which are strung on a complex of wires in such a way that several wires pass through each core. Combinations of electrical impulses on these wires alter the magnetic states of the cores. A line of cores, some magnetized and some neutral, represents a number or other collection of symbols in much the same way as a combination of dots and dashes stands for a word in Morse code. Up to 32,768 of these 'words' can be stored in the 704's high-speed magnetic core memory. Additional 'words' can be held in auxiliary storage by attaching magnetic drum units."

Tracking the Man-Made Satellite

A complex and elaborate "recording" system" will be used to keep track of the tiny sphere after it is launched in space.

Some time during the International Geophysical Year that begins July 1, 1957, there will culminate one of the most ambitious experiments - and certainly the best-publicized - in all scientific history. From the Patrick Air Force Missile Test Center on Cape Canaveral, Florida, a tiny, man-made moon will be launched. It will be carried by rocket to a height of 200 to 300 miles, then pushed horizontally to a speed of 17,000 to 18,000 miles an hour. If all goes well, it will then settle itself in an elliptical orbit around the earth, there to stay for several weeks, or perhaps a year, or perhaps even longer. Science will have taken its first major step into outer space.

Nobody has ever tried anything like this before; hundreds of uncontrollable variables make the outcome of the experiment impossible to predict. One of the largest imponderables is the path that the satellite will take. At this stage of the moon-making art, it is impossible to control or foretell the exact speed of the satellite, its height above the earth's surface, the inclination of its orbit to the equator, or the orbit's shape. Thus, the tiny globe, measuring less than two feet in diameter, could easily become lost to view in the sky like a toy boat misplaced in the Atlantic Ocean.

To forestall any such comi-tragic ending to the experiment, scientists plan to make wide use of electronic tracking and computing equipment. At the heart of all satellite-watching operations will be the fastest large-scale digital computer manufactured by International Business Machines Corporation - the "704" Electronic Data Processing Machine.

The 704 computer installation will be housed in Washington, D. C., in a large building already beginning to fill up with equipment. This equipment will include not only a central data-processing or calculation unit, but also a platoon of subsidiary units to handle such functions as printing, reading, recording, and conversion from one form of data-input (such as punch cards) to another (for example, magnetic tape). This high-powered installation will be served by its own power supply. It will also have its own air-conditioning system to carry off the heat it generates in operation.

Dr. John P. Hagen, director of "Project Vanguard," is shown here with a full-scale cutaway model of the earth satellite designed by scientists working under his direction at the Naval Research Laboratory in Washington. D.C. The instrumentation shown inside includes telemetering equipment which will transmit a radio signal to earth after satellite has been sent into space. Information is then relayed to computer.

Heading the staff of the computer installation will be Dr. Paul Herget, noted astronomer who is director of the Cincinnati Observatory and a consultant to the Naval Research Laboratory. Dr. Herget is familiar with IBM equipment, having used the 704 computer's forerunner, the 701, in a widely applauded planet-tracking operation two years ago. By carefully computing the orbit of a minor planet named "Athalia," which had been discovered by astronomers and subsequently lost again, Dr. Herget and the 701 pointed to the precise spot in the sky where "Athalia" ought to be. It was.

To understand how the Vanguard Computing Center will operate, it is useful to know exactly where it fits into the satellite program as a whole. Like numerous other International Geophysical Year (IGY) programs, the satellite experiment is designed for the specific purpose of expanding scientific knowledge of the earth. Scholars and scientists in many fields will observe the satellite, gleaning information from it on such subjects as solar radiation, cosmic rays, meteors, the earth's gravitational field and atmosphere. The actual launching of the moon, a task dubbed "Project Vanguard" because it must precede all other parts of the satellite program, will be carried out by the U. S. Army, Navy, and Air Force, under general Navy management. The launching has been made a military responsibility simply because the military services have had more practice than anyone else in building and firing rockets.

Three rocket stages with a length of 72 feet and a maximum diameter of 45 inches are expected to put the man-made moon in its orbit. The first stage, a Viking-like rocket carrying several tons of liquid fuel, will push the satellite up to a height of 35 to 40 miles. The second stage, also a liquid-fueled rocket and probably - like the first stage - controlled from the ground, will blast upward to 130 or 140 miles, reaching a speed of more than 10,000 miles an hour. After the second-stage fuel burns out, the momentum of the assembly is expected to carry it somewhere between 200 and 300 miles above the earth. The second-stage rocket hull will be jettisoned, and the third stage will begin to fire.

Now an extremely critical set of maneuvers will take place. They will not be controllable from the ground, but will depend entirely on pre-set automatic devices. These devices are counted on to direct the final rocket on a course roughly parallel with the earth's surface, and to hold it on that course until it reaches a speed as near as possible to the desired 17,000-plus miles per hour.

Finally, the satellite will be ejected from the rocket to travel space on its own. Like the natural moon, it will be held in its orbit by a compromise of centrifugal force and the earth's gravity. The shape of the orbit will be determined by the direction and speed at which it leaves the last rocket. Too great a deviation from the desired speed and direction will result in the satellite's (1) cutting down into the top layers of atmosphere, where friction will cause it to disintegrate in white heat like a meteor; or (2) establishing an orbit that carries it so far away from the earth as to make effective observation extremely difficult or virtually impossible.

If all goes as planned, the artificial moon will settle into an orbit somewhere between these extremes. It will travel in the same general direction as the earth's rotation, most probably at an inclination of 30 to 45 degrees to the equator. Thus, it will be seen to rise in the west and set in the east. It is expected to circle the earth roughly once everyone and one-half hours. Scientists assume that, unlike the natural moon, it will meet just enough resistance from air and other particles to slow it down gradually, until finally it drops into denser atmosphere and burns up.

Since the satellite's orbit cannot be predicted prior to the launching, there is no way in which observers can be told now where to look for it in the sky. The tiny moon may be visible for brief periods under certain conditions at dawn and dusk, when it reflects the sun's rays at just the right angle, but this cannot be counted on as a foolproof way to keep track of the satellite. Some means must be provided to keep it under continuous observation. This is where the electronic computer center comes in.

Inside the satellite will be, among other instruments and devices, a miniature radio transmitter from which will emanate a continuous signal. This signaling system is named "Minitrack," in reference to the midget size of the equipment. Its signal will be picked up by a series of ground Minitrack stations located roughly in a north-south line extending from the mid-latitude region of the U. S. to the latitude of Chile in South America. Each station will take several readings as the satellite passes overhead; the readings will each consist of a precise placement of the satellite in the sky as measured from the station, together with an exact time of measurement.

These readings will be relayed from the Minitrack stations to a communications center in Washington, D. C. From here, the readings will go by direct teletype to the Vanguard Computing Center.

Immediately upon receipt at the Computing Center, the Minitrack measurements will be translated into punched-card form. The cards will then, in most cases, be fed directly into the 704 computer for a complex series of calculations. Cards can be used effectively when there is a relatively small amount of input data, as in the case of the satellite measurements, to be subjected to a large amount of manipulation in the computer. If the input data were greater - as in the case of business accounting records, for example - the punched-card data would be transferred to magnetic tape, which can be "read" electronically at vastly higher speeds than can cards.

Taking the Minitrack sightings as points along the satellite's orbit, the computer will, in effect, connect the points with a line and thus calculate the full orbit. It will continually recalculate the orbit throughout the life of the satellite. As the midget moon completes more and more revolutions, and as ever more measurements are made, the computer's accuracy will steadily increase. Before long, the calculated orbit will even include perturbations, or "wiggles," caused by variations in the earth's gravitational field, attraction of the natural moon and other heavenly bodies, and other factors-perhaps including some not now foreseen.

The computer will have other jobs to do besides marking out the satellite's true orbit. One of the most complex tasks will be that of calculating the man-made moon's shadow path on the earth's surface, or, to put it more accurately, the path traced on the surface by an imaginary vertical line drawn from ground to satellite. The computer will be able to predict this shadow path in advance. Then, by carrying its calculations still further, it will be able to work out a useful - in fact, indispensable - timetable for the benefit of official visual tracking stations and individual scientific observers participating in IGY. The computer will tell each of these observation posts exactly where and when to aim its telescope so that the satellite passes through the field of vision. Without this precise timetable, telescopic observers would have small hope of catching the tiny moon. It will traverse the sky at a rate of one degree, or roughly two diameters of the natural moon, per second.

These calculations are not easy. While the satellite is in its orbit, it will be independent of the earth's rotation beneath it. Each time the little moon completes a circle, the earth will have rotated 1400 to 1600 equatorial miles to the east. Thus, if the satellite is launched at an angle of 40 degrees to the equator, its shadow path after twenty or thirty revolutions will be a curved line that weaves back and forth between 40 degrees north latitude and 40 degrees south, crisscrossing itself many times.

If a precise telescope-aiming timetable were worked out by human computers with paper and pencil, they could never keep pace with the fast-moving satellite - much less get ahead of it and predict its course. It will take an electronic computer, capable of such feats as multiplying or dividing approximately 4700 ten-digit numbers per second, to keep up with the required pace.

In making its calculations, the computer will rely principally on a high-speed magnetic core storage, or "memory." This storage will contain the computer's instructions, now being worked out and programmed in the computer by Vanguard and IBM experts. When the various tracking-station data are submitted to the computer, it will act on the data in accordance with its memorized instructions.

Essentially, the computer's storage function works by means of doughnut-shaped cores, about the size of pinheads, which are strung on a complex of wires in such a way that several wires pass through each core. Combinations of electrical impulses on these wires alter the magnetic states of the cores. A line of cores, some magnetized and some neutral, represents a number or other collection of symbols in much the same way as a combination of dots and dashes stands for a word in Morse code.

Up to 32,768 of these "words" can be stored in the 704's high-speed magnetic core memory. Additional "words" can be held in auxiliary storage by attaching magnetic drum units. The 704 can also control ten magnetic tape units with a capacity of 900,000 "words" each.

The results of the Vanguard 704's computations will flow from the machine in three principal forms. Some of the information will come out in printed form, by means of a direct printer attached to the 704. Some will be on magnetic tape, for printing later on a tape-to-print device. Still other information will be presented in visual form on an ingenious device known as the Cathode-Ray Tube Output Recorder. This device will picture the computer's calculations graphically. It will show, for example, the actual shape of the satellite's orbit as plotted by the 704. It will also show the shape of the shadow path, or any other aspect of the satellite's travels that can usefully be displayed in visual form.

This recorder actually incorporates two cathode-ray tubes. One, a 21-inch tube, is used for immediate display of information worked out in the computer. The other, a seven-inch tube, is designed to work with a 35-mm. camera for recording purposes. This recording device will be used to advantage in the satellite program. Photographs of the midget moon's shadow path, together with marked-off arrival times, will be superimposed on maps of regions having favorable observing conditions.

In the U. S., people living in the southern half of the country will have the best chance of seeing the satellite. The angle of inclination at which it will be launched has not yet been announced, but a general assumption is that the angle will neighbor 40 degrees. The 40th parallel runs through Philadelphia in the east and about 150 miles north of San Francisco in the west; thus, moon-watching conditions will be most probably favorable east, west, or south of these cities.

Visual observation of the satellite will become increasingly important as time goes on. Some weeks after the artificial moon is launched, if it stays in orbit that long, the batteries powering its Minitrack transmitter will die. From then on, all measurements will have to be made optically, or by other means that require no help from the satellite itself. Long before this time, however, the computer will have reached a fine enough degree of accuracy in its orbit calculations so that the tiny sphere, though no longer calling out its own position, will never be lost in the sky as long as it continues to revolve.

Where will be the profit in this program, aside from the sheer excitement of it? The profit, scientists hope, will lie in a flood of new and useful knowledge that can be had from this and other satellites almost certain to be launched in years to come. Many observation posts, not directly connected with Project Vanguard, will be watching the satellite as it speeds around the planet. The Smithsonian Institution, for example, plans a large-scale moon-watching operation, as do numerous universities and other scholarly and scientific bodies throughout the world. Most of them will be aided by the Vanguard Computing Center.

The satellite's orbit itself will offer much information to observers. The earth is not a perfect sphere; nor is its mass uniform throughout. The perturbations of the satellite's orbit, subjected to various calculations, will add to present knowledge of these irregularities. Another area of inquiry is the nature of space at the 200-mile-and-up level. It is supposed to contain tiny meteoric particles that fall in a continual rain toward the earth, as well as highly rarified air. The drag effects of these substances will be measurable in the satellite's orbit, thus offering a clue to their density.

Inside the satellite will be about ten pounds of instruments (total weight of the sphere: a little over 20 pounds). These instruments will gather data about the sun's radiation, cosmic rays, and other phenomena that scientists have not been able to assess accurately because the earth's atmosphere interferes. Sensitive receiving equipment on the ground will pick up the data recorded by the space-travelling instruments.

Though the first man-made satellite has not yet left the ground, scholars and scientists are already speculating delightedly about future moons. As the science of rocketry progresses, it is altogether likely that fuels will be developed to provide more thrust per pound. At present, it takes a colossal tonnage of propellant to hoist a 20-pound sphere into an orbit; the satellite itself is only a minute fraction of the vehicle's total weight. As new fuels are developed, it may be possible to launch larger satellites, capable of carrying more instruments and gathering more data for science. Whatever is done in the field in years ahead, however, there is almost certain to be an electronic computer handling a key phase of the program.

Posted November 14, 2022
(updated from original post on 3/24/2014)