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| South Pole Diaries 2000/01 |
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Saturday
9th December 2000
From
John Storey.....
Today was the day of the zig-zags.
After the initial excitement of making our first ever measurements
at Dome C began to fade, we had to confess to each other that
the data did look a bit on the weird side. Instead of the
signal from the sky smoothly increasing as we looked at ever
greater angles from the zenith, it was jumping up and down
in a completely regular but nevertheless inexplicable pattern.
Naturally we had lots of theories as to what might be going
wrong, but as the day wore on we seemed to be making little
progress. Finally we tracked it down to the stepper motor
that drives our rotator mirror. We were running a small current
through its windings to keep the mirror rigidly fixed at each
position where we took data. This current was interfering
with our extremely sensitive detector, and basically messing
everything up. Switching off the current solved the problem
completely.
I have never been a fan of stepper
motors, as their deceptive simplicity hides a capacity for
pure evil. Today's experience has done little to change that
opinion. In fact, I may go so far as to write a glossary entry
on stepper motors.
With that problem solved a new one
has emerged; namely that our signal becomes very noisy at
one particular elevation angle. At first we thought it was
just the sun getting into our beam, but then the sun moved
on the way it does and the noise was still there.
 Just
after breakfast a Twin Otter arrived with Karim and Jean-Michel
from the University of Nice. They are here to perform a series
of balloon launches to measure the microthermal turbulence
of the atmosphere as a function of altitude. This will complement
the work done a few years ago at the South Pole by the late
Rodney Marks, in collaboration with Jean Vernin.
This is the first Twin Otter we've
had for a few days, and it was good to see several boxes of
fresh fruit and vegies being unloaded as well.
After lunch I spent some time discussing
my impending departure from Dome C and return to Sydney. It
will involve a Twin Otter flight to McMurdo, then a flight
in a US C130 back to Christchurch. We called McMurdo on the
HF SSB rig, and with any luck they are now organising a seat
on a Hercules for me.
Tomorrow I have been asked to give
the inaugural Dome C Science Talk in the Free-time Tent. As
there are no A/V facilities I will have to just stand up and
speak, and maybe get Paolo to do some street theatre to accompany
the talk.
John
New glossary entry!
Stepper Motor. An electromechanical
device which is very simple in concept yet surprisingly complicated
in detail. Failure to appreciate this has been one of the
greatest sources of human misery since the invention of Lotto.
Were it not for the fact that they are extraordinarily useful
little devices I would have nothing to do with them.
 
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