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Summary
Initial
testing on the ground did not go completely smoothly.
The circulator component of the Cryo-Cooler occasionally
experienced decreased speed and unexpected stops.
At times it could be re-started readily, and on
other occasions an extended warm-up was required
before the machine could be restarted. After a great
deal of effort and study, engineers eventually located
the problem.
As part of the circulator loop, the circulator is
a rotating impeller that forces the cooled neon
gas through NICMOS (or mock-up) to cool the detectors.
The circulator loop was the only part of NCS that
could not be sealed in a controlled environment
since it was meant to be connected to NICMOS in
orbit.
Because of this, the internal surfaces of the tubing
were occasionally exposed to room temperature air.
Small but unacceptable amounts of moisture condensed
on internal tubing walls. During cold operations,
the moisture migrated into the circulator and formed
ice films in critical parts of the machine. If a
sufficient amount of ice built up, the rotor could
not be operated properly. Under these conditions,
a small amount of cumulative damage resulted from
this contamination.
In the end, the problem was eliminated by purging
the system with dry gas, using tighter o-ring seals,
and on top of that, purging the area around the
seals.
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Dr.
Anne Marie Russell on problems during testing. |
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