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Charting the launch procedure
The pathfinder
was steadily making its way west at around 12 - 15 miles per hour when
we came in this morning. The pathfinder sends back information
for a while on its altitude, speed and direction before its
instrumentation runs out of power. Then the balloon becomes
"derelict." In the case of such a small balloon and payload,
becoming derelict is not that much of a concern. They pathfinders
come down and are never recovered. In the case of the large
long-duration balloons with large payloads onboard, becoming derelict
is a pretty serious problem since millions of dollars and more
importantly, human lives may be at stake.
We continued doing whopper runs today. By the
end of the day, our cumulative whopper count since we first turned the
instrument on was 112. Bob and I also began to discuss the
program for the first few critical hours of flight. At the
beginning of the flight, we will have the ability to send comands and
receive all of our data over line-of-sight. During this time, it
is important to set all of the voltages and discriminators to the right
levels so that TIGER will be sensitive to the right kinds of particles.
As I've mentioned before, our scintillator detectors
are most sensitive to the charge of the particle that passes through
them. The larger the charge (and also, the heavier the particle)
the more light that is released to the photomultiplier tubes
(PMT). Since each photomultiplier pulse is shaped and sent into a
12-bit analog-to-digital converter, each phototube has a dynamic range
of 4096 channels. In other words, a lighter, lower charged
particle, such as neon, passing through the scintillator will cause a
scintillator PMT to peak in a lower channel than a heavier particle
with more charge, such as iron. In order to get these various
particles to cause the PMTs to pulse in the right channel, it is
necessary to set the high-voltage of the PMT at the right level.
Since iron is much more abundant than any other element near to it on
the periodic table, TIGER will detect enough of it early on in the
flight so that we can use it to decide where to set our high-voltages
so as not to miss any heavier elements. Furthermore, for the most
part, the intensity of cosmic rays gets greater and greater the lower
they go in charge, so it is also necessary to set the PMT thresholds so
that they will ignore the lighter cosmic rays and concentrate more on
the heavier ones. All of this should be done within the first few
hours after launch, if all goes well.
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