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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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Breaking the Problem Down

A systematic flow diagram of the NCS during testing.
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.


More . . .
Dr. Anne Marie Russell on problems during testing.