  The SuperNova/Acceleration Probe (SNAP) will measure precisely the
cosmological expansion history over both the acceleration and deceleration
epochs and thereby constrain the nature of the dark energy that dominates our
universe today. The SNAP focal plane contains equal areas of optical CCDs and
NIR sensors and an integral field spectrograph. Having over 150 million pixels
and a field-of-view of 0.34 square degrees, the SNAP NIR system will be the
largest yet constructed. With sensitivity in the range 0.9-1.7 microns, it will
detect Type Ia supernovae between z = 1 and 1.7 and will provide follow-up
precision photometry for all supernovae. HgCdTe technology, with a cut-off
tuned to 1.7 microns, will permit passive cooling at 140 K while maintaining
noise below zodiacal levels. By dithering to remove the effects of intrapixel
variations and by careful attention to other instrumental effects, we expect to
control relative photometric accuracy below a few hundredths of a magnitude.
Because SNAP continuously revisits the same fields we will be able to achieve
outstanding statistical precision on the photometry of reference stars in these
fields, allowing precise monitoring of our detectors. The capabilities of the
NIR system for broadening the science reach of SNAP are discussed.
