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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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Inside of NICMOS

The light detectors of NICMOS are contained in a cryostat which kept them cool with a large block of Nitrogen Ice.

A High-Tech Thermos

A schematic of the cyrogenic cryostat. The heat leak which caused the nitrogen ice to deplete prematurely is shown on the enlarged diagram.
Just as a camera for recording visible light must be dark inside to avoid exposure to unwanted light, a camera for recording infrared (IR) light must be cold inside because, in the infrared, warm objects glow. In addition, the detectors must also be cold - photoconductive infrared detectors, when warm, effectively generate their own glow (called dark current).

To make sure that NICMOS records infrared light properly, the sensitive infrared detectors in NICMOS must operate at very cold temperatures - below -321 degrees Fahrenheit, or 77 Kelvin.

The instrument's detectors (less than a square inch in size) were cooled inside a cryostat (a thermally insulated container much like a thermos bottle). When NICMOS was installed, the cryostat contained a 230-pound block of nitrogen ice.

Soon after NICMOS was operational, an unexpected heat source was detected and it was apparent the nitrogen ice would be prematurely depleted in about 2 years rather than the expected 5 years.

To compensate, NASA and the scientific community agreed to have Hubble perform more NICMOS observations than originally scheduled in its two years of operation. The setback to infrared science still remained however, and a solution was needed.


More . . .
View an interactive panorama of one of Hubble's axial bays (reproduction in cleanroom). Click and drag mouse to move.