[LINK] Telstar, 50 this week

[stephen at melbpc.org.au]

Telstar, first telecom satellite, launched 50 years ago

By: Martyn Williams (IDG News Service) 10th July, 2012
http://www.arnnet.com.au/article/430140/telstar_first_telecom_satellite_la
unched_50_years_ago/


"Intended as an experiment at the time, Telstar paved the way for the 
more than 300 telecom satellites orbiting the Earth today."

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.

Photos: http://www.arnnet.com.au/slideshow/430193/pictures_telstar_50_-
_little_satellite_launched_an_industry/

--
Cheers,
Stephen