The special “notched one” pulse that was invented to fool Telstar I command decoder.
The special “notched one” pulse that was invented to fool Telstar I command decoder.
What could be done about this? The answer seemed to be to devise a new type of pulse—a pulse that would be enough like a one so that it would pass through the one gate and advance the counter, but, at the same time, be enough unlike a one so that the one gate would not store it in its memory. This led to the invention of the special long pulse with a dip or notch in it that is shown inthe diagram above. When we tested it in the laboratoryon one of the duplicate decoders we had exposed to radiation, this new notched pulse worked as we hoped it would. It passed through the one gate and advanced the counter, but was not stored as a one in the one gate’s memory. Thus it fooled the decoder by doing just what a zero is supposed to do, even though it had gone through the one gate rather than the zero gate.
Magnetic tapes of special codes using notched ones in place of zeros being prepared for use.
Magnetic tapes of special codes using notched ones in place of zeros being prepared for use.
But the real test was yet to come. Special modified signals for two of the fifteen Telstar commands, using our new notched ones in place of the usual zeros, were put on magnetic tape (seephotograph). Then, on December 20th, when Telstar made its 1492nd pass over Andover, Maine, a group of tired engineers huddled about the mass of equipment they had assembled. Finally, on the third try, the notched pulses were successful; Telstar’s telemetry flashed back the word that the proper relay had operated upon command.
We now wanted to get Telstar to do something that had seemed to work in the laboratory. The transistors most affected by radiation were those operating under continuous reverse bias, to whose surfaces unwanted ions were attracted. If we removed the voltage from these transistors, we felt that the ionization layer would be dissipated, and they would act normally again. Our plan was to prepare a complete taped program of all fifteen commands, and carefully disconnect Telstar’s storage battery (using command SS). Then, when the satellite went into eclipse, there would be no power available from the solar cells either, and—if our calculation was right—thecomplete lack of voltage ought to restore the transistors to working order. This was a hazardous procedure, for if something went wrong we might have a completely silent satellite on our hands.
As it turned out, an accident did happen—but one of a different and much more fortunate kind. On December 27th Telstar misinterpreted our “trick” commands and disconnected its own battery before we asked it to. Then, as the satellite went into the earth’s shadow, we held our breath while all its power stopped and the telemetry went silent. But, as we had hoped, a rest period with all power removed from the deteriorated transistors apparently made them work almost normally once again. On January 1, 1963, we were able to disconnect the battery in regular fashion—that is, using the one-and-zero code. After this was done, and all power had been removed, both decoders again would operate when given normal commands (actually, the first one restored to duty was decoder No. 2, which had gone out of order first, back in August).
For more than a month Telstar I behaved as it should, and our communications experiments, including television broadcasts, were resumed on January 3rd. During this time we used both normal commands and our special notched-pulse modified commands. Whenever normal commands became intermittent we used the modified commands to disconnect the battery for several eclipses.
Our good fortune, however, did not last. Continued exposure to radiation apparently led to further damage to Telstar I’s transistors. By February 14th, disconnecting the storage battery no longer returned the decoder to normal, and we could operate only with our modified commands. And, on the 21st, the satellite apparently misinterpreted a command, disconnected its storage battery, and went silent. Since then, none of our modified commands has been able to bring back its voice. There is still a possibility that Telstar I may recover if it remains out of the high-radiation part of space for a long enough period—but as time goes by this appears less likely.
However, our work was not in vain. Because we pinpointed the effects of radiation on the transistors in Telstar I, this problem was counteracted on the Telstar II satellite launched on May 7, 1963 (seepage 31). To avoid the worst of the radiation effects, the second Telstar is in a considerably larger orbit, which causes it to spend less time in the heaviest high-energy Van Allen belt regions. It carries new radiation detectors with much greater measuring capacity. And in one of Telstar II’s command decoders we are using a new type of transistor, which we hope will not be affected nearly as much by radiation as were the ones in Telstar I’s ill-fated decoders.
E. Jared Reidwas born in Hartford, Connecticut, and received a B.S. from Trinity College in 1956, a B.E.E. from Rensselaer Polytechnic Institute in 1957, and an M.E.E. from New York University in 1959. He joined Bell Telephone Laboratories in 1957, and has worked on the design and testing of the Time Assignment Speech Interpolation (TASI) system for the transatlantic cable, as well as on transistor circuits for the Telstar satellite.
E. Jared Reidwas born in Hartford, Connecticut, and received a B.S. from Trinity College in 1956, a B.E.E. from Rensselaer Polytechnic Institute in 1957, and an M.E.E. from New York University in 1959. He joined Bell Telephone Laboratories in 1957, and has worked on the design and testing of the Time Assignment Speech Interpolation (TASI) system for the transatlantic cable, as well as on transistor circuits for the Telstar satellite.
Now, having read Part II ofSatellite Communications Physics,you should have an idea how we predict the orbit of an artificial satellite and how we find out where it points while passing a thousand miles above our heads. You can see how we pick the best material to cover its surface with and how we protect its solar cells from the hazards of space. And you have watched the steps we would take when our satellite stops working properly.
It would, we admit, take a little more experience to solve problems like these on your own—and to deal with all the other complications of satellite communications. But we hope our brief glimpses into the laboratory have shown what this experience might be like. Our six case histories have only scratched the surface, but they should give you a good idea of the fascinating work that goes into practical science and engineering. They should show that something like Project Telstar doesn’t succeed only because of far-sighted, imaginative thinking—nor only because of ingenious engineering. It draws upon the best of both of these.
Along the way, we hope you have noticed some important guideposts—things like Newton’s law of gravitation, the law of reflection of light, the Stefan-Boltzmann law. They typify the basic principles of physics that engineers and scientists, whatever they do, must always keep in mind. No matter how exotic or up-to-the-minute the application, the ground rules of physics must be followed. If we have convinced you of this, we have done what we set out to do!
If you would like to read further about satellite communications in general or get some information about the case histories in Part II, you may be interested in using the following reading list. The references under each of the subheadings are listed chronologically; they include books, reports, technical papers, and magazine articles. As you can see, some of these ought to be understandable by almost anyone, but others are quite technical in nature.
For further background in the basic physical principles that are discussed in Part II, you may refer to many good high school and college physics texts. An increasing number of useful physics books—both originals and reprints—are now being published in paperback form.
Arthur C. Clarke, “Extra-Terrestrial Relays—Can Rocket Stations Give World-Wide Radio Coverage?,”Wireless World, October 1945, page 305.
John R. Pierce, “Orbital Radio Relays,”Jet Propulsion, April 1955, page 153.
John R. Pierce and Rudolf Kompfner, “Transoceanic Communication by Means of Satellites,”Proceedings of the I.R.E., March 1959, page 372.
John R. Pierce, “Exotic Radio Communications,”Bell Laboratories Record, September 1959, page 323.
Steven M. Spencer, “Dial ‘S’ for Satellite,”The Saturday Evening Post, January 14, 1960, page 13.
Space Electronics Issue,Proceedings of the I.R.E., April 1960.
William Meckling, “Economic Potential of Communication Satellites,”Science, June 16, 1961, page 1885.
Special Issue on Project Echo,Bell System Technical Journal, July 1961.
C. C. Cutler, “Radio Communication by Means of Satellites,”Planetary and Space Science Journal, July 1961, page 254.
W. C. Jakes, Jr., “Project Echo,”Bell Laboratories Record, September 1961, page 306.
John R. Pierce, “Communication Satellites,”Scientific American, October 1961, page 90.
United States Senate, Committee on Aeronautical and Space Sciences,Communication Satellites: Technical, Economic, and International Developments(staff report), U. S. Government Printing Office, Washington, 1962.
L. J. Carter, editor,Communications Satellites, Academic Press, New York and London, 1962.
“Situation Report on Communications Satellites,”Interavia, June 1962, page 749.
Leonard Jaffe, “Communications by Satellite,”International Science and Technology, August 1962, page 44.
“Communicating by Satellite,”Business Week, October 27, 1962, page 86.
Rowe Findley, “Telephone a Star,”National Geographic, May 1962, page 638.
Louis Solomon,Telstar, McGraw-Hill Book Company, New York, 1962.
Special Telstar Issue,Bell Laboratories Record, April 1963.
Special Telstar Issue,Bell System Technical Journal, July 1963.
1. How Do We Calculate a Satellite’s Orbit?
Mario Iona, “Satellite Orbits,”The Physics Teacher, May 1963, page 55.
A. J. Claus et al., “Orbit Determination and Prediction and Computer Programs,”Bell System Technical Journal, July 1963, page 1357.
2. What Color Should a Satellite Be?
P. T. Haury, “Thermal Design of the Electronics Canister,”Bell Laboratories Record, April 1963, page 161.
J. W. West, “Space Hardware Aspects of the Satellite,”Bell Laboratories Record, April 1963, page 167.
Peter Hrycak, et al., “The Spacecraft Structure and Thermal Design Considerations,”Bell System Technical Journal, July 1963, page 973.
3. How Do We Make Optical Measurements on a Satellite?
W. C. Jakes, Jr., “Participation of the Holmdel Station in Project Telstar,”Bell System Technical Journal, July 1963, page 1421.
4. How Do We Keep Solar Cell Power Plants Working in Space?
D. M. Chapin et al., “The Bell Solar Battery,”Bell Laboratories Record, July 1955, page 241.
G. R. Frost,From Sun to Sound, Bell Telephone Laboratories, New York, 1961.[6]
F. M. Smits, K. D. Smith, and W. L. Brown, “Solar Cells for Communications Satellites in the Van Allen Belt,”Journal of the British I.R.E., August 1961, page 161.
D. M. Chapin,Energy from the Sun, Bell Telephone Laboratories, New York, 1962.[6]
R. E. D. Anderson et al., “The Satellite Power System,”Bell Laboratories Record, April 1963, page 142.
K. D. Smith et al., “The Solar Cells and Their Mounting,”Bell System Technical Journal, July 1963, page 1765.
5. Would Time Delay Be a Problem in Using a Synchronous Satellite?
G. M. Phillips, “Echo and Its Effect on the Telephone User,”Bell Laboratories Record, August 1954, page 281.
W. A. van Bergeijk, J. R. Pierce, and E. E. David, Jr.,Waves and the Ear, Anchor Books (Science Study Series paperback), Doubleday & Company, New York, 1960.
R. P. Haviland, “The Synchronous Satellite,” inCommunications Satellites, L. J. Carter, editor, Academic Press, New York and London, 1962, page 113.
6. How Do We Repair an Orbiting Satellite?
D. S. Peck et al., “Surface Effects of Radiation on Transistors,”Bell System Technical Journal, January 1963, page 95.
“Fixing Up Telstar,”Time, January 18, 1963, page 48.
E. P. Moore and W. J. Maybach, “Satellite Command and Telemetry Systems,”Bell Laboratories Record, April 1963, page 156.
J. S. Mayo et al., “The Command System Malfunction of the Telstar Satellite,”Bell System Technical Journal, July 1963, page 1631.
Note: TheBell Laboratories Recordis published by Bell Telephone Laboratories, Incorporated, 463 West Street, New York 14, New York.The Bell System Technical Journalis published by the American Telephone and Telegraph Company, 195 Broadway, New York 7, New York.
Note: TheBell Laboratories Recordis published by Bell Telephone Laboratories, Incorporated, 463 West Street, New York 14, New York.The Bell System Technical Journalis published by the American Telephone and Telegraph Company, 195 Broadway, New York 7, New York.
Ronald M. Foster, Jr.,was born in Plainfield, New Jersey, and received an A.B. degree from Harvard College in 1948. He joined Bell Telephone Laboratories in 1956, and is a member of the Educational Aids Department of the Public Relations and Publication Division. He is engaged in development of material for the Bell System Aid to High School Science Program.
[1]This is obtained fromk=gR², wheregis the acceleration due to gravity andRis the radius of the earth. (Here, we can usek= 96,500 miles³ per second².)[2]Donald R. Herriott of Bell Labs had suggested using plane reflectors on satellites as long ago as 1957—although his idea was that this would increase their visibility, rather than aid in determining their attitude.[3]This method was developed by D. W. Hill of Bell Telephone Laboratories.[4]We will not attempt to go into all the details of semiconductor physics here. If you would like to know more about how solar cells work, refer to the Suggested Reading onpage 88.[5]See pages42and43.[6]Published as part of the Bell System Aid to High School Science Program.
[1]This is obtained fromk=gR², wheregis the acceleration due to gravity andRis the radius of the earth. (Here, we can usek= 96,500 miles³ per second².)
[2]Donald R. Herriott of Bell Labs had suggested using plane reflectors on satellites as long ago as 1957—although his idea was that this would increase their visibility, rather than aid in determining their attitude.
[3]This method was developed by D. W. Hill of Bell Telephone Laboratories.
[4]We will not attempt to go into all the details of semiconductor physics here. If you would like to know more about how solar cells work, refer to the Suggested Reading onpage 88.
[5]See pages42and43.
[6]Published as part of the Bell System Aid to High School Science Program.
Wraparound cover image