R. M. Foster

In this section we will go into some detail about Project Telstar. We do this because much of what we learned from this project applies to the general field of satellite communications. The problems that were faced and solved are typical of the challenges that working engineers and scientists must meet today. And there is, of course, another reason to put this much emphasis on Telstar: The six case histories in Part II of our book were written by men who were involved with that project. Before reading their accounts it will be helpful for you to have some background information about it.

What Project Telstar Was Designed To Do

Even its most enthusiastic planners at Bell Telephone Laboratories never expected the sensation that Telstar caused. Although it was a deadly serious venture—one of the steps along the way toward putting together a workable satellite communications system—its success made it the inspiration, among other things, of cartoons, jokes, and a couple of popular songs. “Telstar” soon became a name recognized around the entire globe. Stories about Project Telstar appeared in newspapers in almost every language, in children’s books, in women’s fashion magazines.

On July 10 and 11, 1962, people on two continents saw these scenes on television at the same time, with the aid of the Telstar I satellite

What caused all this stir in the summer and fall of 1962? The answer—now that we look back on it—seems rather clear: For the first time, the whole world discovered that satellite communications was really possible—that peoples separated by oceans could now be united by live television. Space had become an adventure, not just for lonely astronauts, but for everyone right in his living room.

Project Telstar, of course, had more serious objectives:

• to prove that a broadband communications satellite could transmit telephone messages, data, and television;
• to test, under the stresses of an actual launch and the hazards of space, some of the electronic equipment that had been developed for satellite communications;
• to measure the radiation that a satellite would meet in space;
• to find out the best ways to track a moving satellite accurately;
• to provide a real-life test for the special satellite communications antennas and other ground station equipment.

To do its principal job—communications—the Telstar I satellite had to receive a signal from a ground station, amplify it, and then retransmit it on a different frequency back to other points on the earth. This signal had to be strong enough and good enough to be received and understood on the ground.

To do its secondary job—measure radiation and other conditions in space—the satellite had to be equipped with special testing devices and had to have a means of reporting facts about the environment it encountered in space and the effects of radiation on solar cells and transistors.

To let us know how well its equipment was working, the satellite had to record and transmit a large number of measurements—including such things as the temperature and pressure inside the satellite, its orientation with respect to the sun, the current and voltage in various parts of its electronic circuitry. Sending these measurements back to a ground station is called telemetry.

To help with tracking, the satellite had to have a continuous radio beacon signal that could be easily picked up on earth.

Finally, the satellite had to be able to control its equipment by means of signals from the ground. To keep the solar power plant from being overloaded, there had to be some way of “commanding” the satellite to turn itself on or off. As you will read later, this was the one part of the satellite that caused us the most headaches once Telstar I got into orbit.

The Telstar I Satellite—Outside

Telstar’s outer appearance is very familiar by now: a 34½-inch sphere with 72 flat facets, a double row of rectangular openings circling its center, and a short, oddly twisted antenna on one end. Of the 72 facets, 60 are used for the solar cells that are the satellite’s main power source. When Telstar is in sunlight, these cells convert solar energy into electrical power; at full capacity the 3600 solar cells will supply about 15 watts. As time goes by, this power slowly diminishes as the cells are gradually damaged by such hazards of space as radiation particles and micrometeorites. To reduce this damage, the satellite’s cells are covered with a thin layer of man-made sapphire.

Two bands of rectangular openings go around the center of the satellite. The smaller cavities, of which there are 72, are receiving antennas; the 48 larger ones are transmitting antennas. This arrangement allows the antennas to transmit and receive equally well in all directions—except directly along the satellite’s poles.

At one end of the satellite is an entirely separate receiving and transmitting antenna that takes care of all the signals needed for Telstar’s command, tracking and telemetry. The antenna is composed of four metal loops joined in the shape of a helix. It receives the important command signals from the ground that give orders to the satellite’s equipment. It sends reports back to the ground from the special radiation measuring devices and other sensors aboard the satellite, and it also transmits the continuous 136-megacycle radio beacon that can be picked up by ground equipment searching for Telstar.

Six of the satellite’s flat facets are used for special measuring devices. Two different radiation studies are made: finding out how much damage will be done to solar cells and transistors, and determining how many actual energetic particles—protons and electrons—are present in the part of space that Telstar passes through. These different jobs are done by special devices on various facets. One, for example, consists of seven identical silicon transistors, six having different thicknesses of shielding and one being left unshielded—the amount of damage done to each is recorded and reported back to earth. Devices on another facet measure the radiation damage to solar cells protected by various thicknesses of sapphire. For the second radiation experiment—particle counting—four different types of silicon diodes are used as particle detectors. These measure the energy deposited both by protons of three energy levels and by electrons as the satellite passes through belts of natural and man-produced radiation in space.

The Telstar I satellite—outside

telemetry, command and beacon antenna

solar cells for power supply

solar cells to measure radiation damage

receiving antenna

transmitting antenna

transistors used to measure radiation damage

solar aspect cells

mirror

---

The Telstar I satellite—inside (looking at the electronics canister from the top down)

beacon transmitter

traveling-wave tube amplifier

radiation measurement equipment

nickel-cadmium cells (foamed)

Measuring devices mounted on the surface of the Telstar I satellite

particle detectors used to count protons

transistors used to measure radiation damage

solar cells used to measure radiation damage and as solar aspect indicators

particle detector used to count electrons

There are two other special devices: Six single solar cells are spaced at regular intervals around the satellite; these “solar aspect” indicators report the quantity of sunlight hitting them—and thus tell the direction in which the satellite is pointing. Three highly polished metal mirrors are also placed on Telstar; flashes of sunlight reflected from them can be seen in a telescope. To give a precise indication of the satellite’s position, the data obtained from both the solar aspect cells and from the flashes off the mirrors are combined.

The Telstar I Satellite—Inside

Within the white aluminum-oxide outer shell of the satellite is crammed a complicated array of electronic equipment. Surprisingly, most of this gear has to do not with Telstar’s prime function—communications—but with its command and telemetry systems. The reason is that the satellite is an experimental device, not just a spectacular way to relay television programs. Altogether, the satellite’s various electronic circuits contain more than a thousand transistors and almost 1500 semiconductor diodes, plus a single electron tube—a traveling-wave tube used in the communications amplifier.

The satellite itself has a magnesium frame that is covered with aluminum panels. All its electronic components are inside a aluminum canister, 20 inches in diameter, attached to the interior frame by special nylon lacings that reduced vibration inside the canister during launch. When all the components and subassemblies had been carefully put in place and thoroughly tested, the canister was filled with a liquid foam called polyurethane. This material hardens into a very light and rigid solid, completely enveloping the equipment and protecting it from damage and vibration. After the canister was solidly foamed, metal domes were welded onto the ends, and it was enclosed in a many-layered blanket of aluminum-coated Mylar (the same material used in the Echo balloon). To keep its temperature properly controlled, shutters on the canister’s two ends are operated by bellows.

The satellite power system includes more than just solar cells. When operating at full capacity, the satellite’s equipment needs more energy than the 3600 solar cells can provide at one time. So Telstar also uses a storage battery made up of 19 rechargeable nickel-cadmium cells designed for this special purpose. These ensure that the satellite has a continuous and sufficient supply of power, even when all equipment is in operation or when the satellite is passing through the earth’s shadow.

After all electrical tests had been made on the satellite’s components, the electronics canister was filled with liquid polyurethane foam, using this specially developed foam machine

The giant horn antenna at Andover, Maine

Ground Stations for Satellite Communications

Project Telstar is actually an extension into space of microwave communications methods that have been thoroughly proved on the ground. For Project Echo and other early experiments in satellite communications, Bell Laboratories built a large antenna of the type known as a horn-reflector in Holmdel, New Jersey. For Project Telstar, a similar but much larger antenna was designed. It was located in a relatively isolated spot at Andover, in the western part of Maine, where it would be close to Europe. The site is nicely protected by a surrounding ring of low hills—high enough to keep out interfering radio signals, but low enough not to block the satellite when it is near the horizon.

The giant Andover horn is a steel and aluminum structure 177 feet long and 94 feet high that weighs 380 tons. At one end is a giant opening of 3600 square feet; from there the horn tapers down to a cab in which the very sensitive receiver and powerful transmitting equipment is located. The entire antenna—horn, cab, and supporting framework—moves smoothly on tracks that allow it to rotate in a 360-degree circle around its vertical axis (changing azimuth). It also can swing about its horizontal axis from the horizon up to the zenith (changing elevation). Despite its size, the antenna can revolve steadily and precisely in a complete circle in just four minutes.

Signals are beamed to the satellite on a frequency of 6390 megacycles, using modified Bell System microwave equipment and a special traveling-wave tube with an output of 2 kilowatts. Signals come back on a 4170-megacycle frequency at a much lower power level—as small as a trillionth of a watt. They are amplified by a ruby crystal maser that operates at the temperature of liquid helium—just a few degrees above absolute zero. The whole antenna structure and its associated equipment are enclosed in a huge “radome”—a bubble made from Dacron and synthetic rubber only a sixteenth of an inch thick but measuring 210 feet in diameter and 160 feet high. It is one of the largest air-supported structures ever erected.

The Andover ground station includes a lot more equipment—most of it having to do with tracking the satellite, computing its orbits, sending and receiving command and telemetry signals, and interconnecting the satellite with regular telephone and television land links. Most of this is located in a control building about a quarter mile from the giant radome.

The French radome looms over the Brittany countryside

A ground station very similar to the Andover installation has been built by the French National Center of Telecommunications Studies at Pleumeur-Bodou in Brittany. The British General Post Office has established a station at Goonhilly Downs in Cornwall, England, which uses a large, deep parabolic dish rather than a horn-reflector antenna. Both British and French stations participated in the first Telstar experiments. Satellite communications ground stations also have been set up in Fucino, Italy, and near Rio de Janeiro, Brazil, and others are under construction in West Germany and Japan.

The Satellite Goes Into Orbit

At 4:35 a.m. (Eastern Daylight Time) on July 10, 1962, a Thor-Delta rocket launched Telstar I into its orbit, almost exactly according to plan, from the National Aeronautics and Space Administration’s Cape Canaveral base. On Telstar’s sixth orbit around the earth—at 7:26 p.m.—the first transmission to and from the satellite took place. During this pass telephone calls, television, and photos were transmitted between Andover and Holmdel. Some of these signals were also picked up in Europe. On the next day, a taped television program was sent from France to the United States, and a live program came from England via Telstar. During the next four months, more than 400 transmissions were handled by Telstar—including 50 television demonstrations (both black-and-white and color), the sending of telephone calls and data in both directions, and the relaying of facsimile and telephotos.

In addition, the satellite performed more than 300 valuable technical tests. Almost all of them showed remarkably successful results. Radio transmission was as good as was expected. Telstar’s communications equipment worked exactly as it should, with no damage from the shock and vibration of the launch. Temperatures inside the satellite were kept under good control. The satellite was successfully stabilized—prevented from tumbling over and over—by being spun around its polar axis, with the spin rate gradually decreasing, as predicted, from its rate of 177.7 revolutions per minute just after launch. The solar cells worked almost exactly as expected. Much extremely valuable data about radiation in space was reported. The ground stations accurately traced the fast-moving satellite in almost routine fashion.

But it would be asking too much to have everything perfect. Telstar I unexpectedly met radiation in space estimated to be 100 times more potent than had been predicted. As a result, difficulties arose during November 1962 in some of the transistors in its command circuit—and on pages 78 to 85 we tell you what these problems were, how they were discovered, and what steps were taken to overcome them. Some time later the satellite again failed to respond to commands from the ground, and on February 21, 1963, it went silent.

The Second Telstar Satellite

On May 7, 1963, the Telstar II satellite was launched into an elliptical orbit almost twice as large as that of Telstar I, ranging from an apogee of 6697 miles to a perigee of 604 miles. The new satellite circles the earth once every 225 minutes. The higher altitude provides Telstar II with longer periods when it is visible at both Andover and ground stations in Europe, and keeps it out of the high-radiation regions of space for a greater part of the time. The satellite itself is much the same as Telstar I, except for a few minor changes that make its weight 175 rather than 170 pounds. Its radiation measuring devices have a greater range of sensitivity, and there are six new measurements to be reported back to earth. Telemetry can now be sent on both the microwave beacon and, as before, on the 136-megacycle beacon. To help prevent the kind of damage that occurred in the transistors of Telstar I’s command decoders, Telstar II uses a different type of transistor, in which the gases have been removed from the cap enclosures that surround the transistor elements. A simplified method of operation for the giant Andover horn antenna is now in operation, with the autotrack alone being used for precise tracking and pointing. Telstar II’s first successful television transmission took place on May 7, and a new series of technical tests, radiation measurements, and experiments in transoceanic communications has begun.