Telstar, first telecom satellite, launched 50 years ago
- 10 July, 2012 18:09
Fifty years ago this week a Delta rocket roared into space carrying a payload that sparked a revolution in the way the world communicates. On board the rocket, launched on July 10, was Telstar, the first telecommunications satellite.
The story of Project Telstar can be traced back to 1955 when John Pierce, a researcher at AT&T's Bell Labs, began looking at the possibility of using space-based stations for communications.
Beginning in 1960, NASA and Bell Labs experimented with bouncing radio via large, metallic balloons and succeeded in sending a signal across the U.S. But engineers soon realized that the Project Echo technology didn't scale. The demands of television transmission required a balloon much larger than could be made at the time.
In stepped the much more sophisticated Telstar.
At about 34 inches (76.2 centimeters) in diameter, the roughly circular satellite (it actually had 72 sides) would spin on its axis in space as it orbited the Earth. Solar panels occupied most of the faces and charged 19 batteries, "of the type used in rechargeable flashlights but specifically designed for the space environment," read a Bell Labs paper of the time.
The electronics, housed in a 20-inch aluminium tube, consisted of an amplifier that would boost the received signal about ten billion times before it was retransmitted. Original plans called for the satellite to relay two channels of television, but weight restrictions of the Delta launch rocket meant this was cut back to a single channel.
It wasn't just the satellite that required significant engineering work.
Unlike today's communications satellites, which sit 36,000 kilometers, or about 22,400 miles, above the equator so that they appear stationary when viewed from Earth, Telstar was in a much lower orbit and appeared to move across the sky. A sensitive tracking antenna was needed to keep in contact with Telstar as it moved from horizon to horizon. The entire orbit took about two hours and 40 minutes, but the satellite was only in a position to relay signals between the U.S. and Europe for about 20 minutes during each of these orbits.
Bell Labs chose Andover, Maine, as the location for the U.S. tracking station, due to favorable terrain and a quiet radio spectrum. Ground stations were built at Goonhilly in the U.K. and Pleumeur-Bodou in France.
On its first pass over Andover, engineers were able to transmit speech and video between the receiving station and an audience in Washington, D.C. As this was happening, word came from France that the signals were being received. The British were receiving the satellite, but technical problems kept them from initially getting a useable signal.
The subsequent pass was used to demonstrate the transmission of six simultaneous telephone circuits as well as a data transmission. A newsreel of the time excitedly reports the data transmission of 1,000 words per minute.
The first television transmission from Europe came on July 11, when signals were sent from France and the U.K. and were received in Andover.
While these initial transmissions were major achievements, Telstar's primary purpose was as an experimental platform and it was used to conduct over 250 technical tests in the subsequent months.
On Nov. 23, the satellite started providing some valuable but unwelcome data.
The control channel used to command the satellite stopped responding and scientists suspected that space radiation might be messing with some of Telstar's 1,064 transistors and 1,464 diodes. At the time, the high radiation of the Van Allen belt was known, but its effects on sensitive circuitry were not well understood.
Laboratory tests pointed to certain transistors being more susceptible than others and engineers devised a control signal to bypass these components. They managed to get a control signal to Telstar when it was traveling at its closest point to the Earth and successfully regained control.
Demonstrations of TV from Europe to the U.S. resumed in January, but they were to be short-lived. The satellite again started having problems and on Feb. 21 it misinterpreted a command and operated a relay that disconnected most of the electronics from the power source.
While Telstar's life was short and its capability limited, it helped start to answer fundamental questions about satellite communications.
The same concerns, such as the effects of space radiation on electronics and the prediction of a satellite's orbit, are still relevant today with more than 300 communications satellites ringing the Earth to provide television, radio, telephone and Internet relays that touch almost all of our lives.
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is firstname.lastname@example.org
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