This left only radiation damage. We had other good reasons to suspect
this, too. As far back as October 1961, scientists at Bell Labs and
Brookhaven National Laboratories had made an important discovery about
the effect of radiation on a transistor. They found that, when radiation
penetrates the outer shell of a transistor and ionizes the gases inside,
electrically charged particles (ions) tend to collect on the surface and
change the transistor’s electric properties. This effect is particularly
noticeable when a transistor is operating under reverse bias voltage. We
knew that some of the 37 transistors used in each Telstar I decoder
circuit were operating under continuous reverse bias and that they also
had less metal shielding than did those semiconductors in the telemetry
and receiver circuits.
Telstar’s radiation detectors had been telling us that the concentration
of high-energy electrons near the inner edge of the Van Allen belt was
greater than we had expected. We now know this may have come as a result
of man-made high-altitude nuclear explosions, one of which took place
the day before Telstar I was launched. But we had had no reason to
anticipate this extra radiation—it was more than one hundred times the
predicted level—when we tested the transistors to be used in Telstar I.
So we were not too surprised that they were more susceptible to
radiation damage than we had thought they would be.
All this seemed to give us a theoretical explanation for the trouble.
So, after November 23rd, we began looking for laboratory evidence to
confirm our radiation theory. First, two engineers traveled down to
Johannesburg, South Africa. At this time the highest point of Telstar’s
orbit—when it passes through the least Van Allen belt radiation—was over
the southern hemisphere, and it seemed a good idea to command the
satellite when it was under the condition of lowest radiation and see if
anything would happen. However, everything the engineers tried proved
fruitless.
[Illustration: _A duplicate of one of Telstar I’s command decoders,
containing 37 transistors and 191 diodes, being placed in a small
elevator that will lower it into a gamma radiation chamber._]
At our Murray Hill, New Jersey, laboratories we worked on a different
approach. We exposed transistors like those used in the decoders to
large doses of radiation. We also exposed entire spare decoder units to
accelerated radiation to find out where their weakest points were (_see
illustration_). And then we built and tested decoders using
radiation-resistant transistors to see if they worked better. After a
week of intensive laboratory work, we had some pretty good evidence. The
tests of individual transistors definitely showed that heavy radiation
would cause them to deteriorate. Testing of the complete decoders also
led to some failures, and, when we analyzed them, they turned out to be
the kind that would be caused by faulty transistors. We also discovered
that the most sensitive part of a decoder circuit was the zero gate,
which recognizes the zeros in the one-and-zero code that commands the
satellite.
[Illustration: _A typical command signal sent to Telstar I. It
consists of seven pulses: a three-unit “start” pulse and a binary
code made up of three two-unit “one” pulses and three one-unit
“zero” pulses._]