NICMOS covers the wavelength range of 0.8 ^m and 2.5 ^m, and its highly sensitive HgCdTe detector arrays must be cooled to liquid-nitrogen temperatures for optimum sensitivity. Initially the cooling was provided by an onboard exhaustible liquid-nitrogen supply and it operated as such between February 1997 and November 1998 yielding exciting new results on the giant planets, among many other things. However, the cryogen was eventually exhausted and thus the detectors warmed up, reducing the usefulness of the instrument. NICMOS was subsequently revived by the shuttle Servicing Mission 3B (STS-109) in March 2002, which installed an active cooling system for the instrument to return the performance of NICMOS to its designed level.
NICMOS is composed of three cameras: NIC1, NIC2, and NIC3, which form three adjacent FOVs at different angular resolutions. Each camera has a 256 x 256 detector array and 19 different combinations of filters, gratings, and prisms. NIC1 covers a 11 x 11" region of the sky at a resolution of 0.043", NIC2 covers a 19.2 x 9.2" region at a resolution of 0.075", and NIC3 covers a 51.2 x 51.2" region at an angular resolution of 0.2". Most of the filters of NIC1 cover the shortwave-length end of the NICMOS range, while NIC2 has more filters covering the long-wavelength end. NIC3 has yet another selection of filters across the range, and can also operate as a spectrometer with a resolving power of200 and three spectral ranges of 0.8-1.2 ^m, 1.1-1.9 ^m, and 1.4-2.5 ^m, respectively. In addition, NICMOS can also measure the mean polarization at 0°, 120°, 240° between 0.8-1.3 ^m for NIC1, and 1.9-2.1 ^m for NIC2.
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