TELECOM Digest OnLine - Sorted: Re: What Exactly Did "Telstar" Do?

Re: What Exactly Did "Telstar" Do?

Charles G Gray (graycg@okstate.edu)
Tue, 14 Dec 2004 08:09:23 -0600

Telstar I, the first active satellite repeater ("bent pipe") was
launched on 10 July 1962 by NASA, in conjunction with AT&T. If you
"Google" for "Telstar", and look at the first 5 or 6 entries you can
get full details (and some very good photos and diagrams) on the
launch and transmission capabilities. Note that it was only 34.5
inches in diameter, and impossible to see from the Earth. Telstar I
operated from 10 July 62 to 23 November 62 and 4 January 63 to 21
February 63. Transistor failure due to Van Allen Belt radiation
damaged the command subsystem, but it was recovered for the second
short round of tests, until it failed completely. Telstar II operated
from 7 May 63 to May 65.

An earlier satellite, Echo, was launched on 12 August 1960. It was a
passive reflector balloon 33 meters in diameter, made of 0.013 cm
thick aluminized plastic. It orbited at 1000 miles and could be seen
from the Earth. I was living in El Paso, Texas at the time, and if we
went out into the desert away from the "ground light" we could see it
pass overhead. It was in an almost perfect circular orbit, inclined
at 47.3 degrees. Communications were established between Jet
Propulsion Laboratories (JPL) in Goldstone, CA and Bell Laboratories
at Holmdel, NJ. JPL used a 26 meter parabolic dish antenna with 10 Kw
transmit power. Bell Labs used a horn reflector with a 6 x 6 meter
aperture. It could support two-way live voice and fax was
demonstrated on 22 September 1960. See "Engineering and Science in
the Bell System - 1925-1980" for more information.

Note that the first transatlantic telephone cable (TAT-1) was not laid
until 1956, and it carried only 36 voice channels. No transatlantic
television capability existed until Telstar. In the 1960's "time
assignment speech interpolation" or TASI was installed on TAT-1 which
allowed 48 voice channels over the 36 cable pairs. TAT-2 was laid in
1959 and had 48 cable pairs supporting 72 voice channels. TAT-3 came
to service in 1963 with 138 pairs for 276 voice channels. Now we are
up to TAT-14, which is a dual reverse protection (self healing) ring,
capable of carrying 16 10 Gb/s on four fiber pairs.

Regards,

Charles G. Gray
Senior Lecturer, Telecommunications
Oklahoma State University - Tulsa
(918)594-8433

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