The NASA Infrared Telescope Facility (NASA IRTF) is a telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawaii. It was first built to support the Voyager missions and is now the US national facility for infrared astronomy, providing continued support to planetary, solar neighborhood, and deep space applications. The IRTF is operated by the University of Hawaii under a cooperative agreement with NASA. According to the IRTF's time allocation rules, at least 50% of the observing time is devoted to planetary science. Telescope The IRTF is a 3.0 m (118" effective aperture) classical Cassegrain telescope. The Cassegrain focus f/ratio is f/38 and the primary mirror f/ratio is 2.5. Several aspects of the design of IRTF are optimized for IR observations. The secondary mirror is undersized to prevent the instrument from seeing the thermal emission from the telescope structure around the primary mirror. The primary mirror itself is 126" in diameter, but only the center 118" is used. A small mirror in the center of the secondary mirror prevents the instrument from seeing its own thermal emission. The f/ratio is long to have a small secondary mirror, again to minimize the telescope's thermal emission. The mirror coatings are chosen to have minimal thermal emission. The emissivity of the telescope is usually below 4%. The secondary mirror is mounted on a chopping mechanism to rapidly switch the pointing of the telescope from target to sky at up to 4 Hz. The IRTF is mounted on a large English yoke equatorial mount. The mount is very stiff, reducing flexure and allowing for accurate pointing of the telescope. Since the telescope is on an equatorial mount, the telescope can observe targets through the zenith without concern for field rotation. The yoke mount prevents the telescope from pointing north of +69 degrees declination. Since the telescope was primarily intended for planetary science, this restriction was considered to be acceptable. Since the telescope is on a heavy mounting, it is relatively immune from vibration or wind shake. Instrumentation The IRTF hosts four facility instruments: SpeX, NSFCam2, iSHELL, and MIRSI. IRTF also hosts a number of visiting instruments. SpeX SpeX is a medium-resolution 0.8-5.4 µm spectrograph built at the Institute for Astronomy (IfA), for the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The primary scientific driver of SpeX was to provide maximum simultaneous wavelength coverage at a spectral resolving