power which is well-matched to many planetary, stellar and galactic features, and at resolving power which adequately separates sky emission lines and disperses sky continuum. This requirement has resulted in an instrument which provides spectral resolutions of R~1000-2000 across 0.8-2.4 µm, 2.0-4.1 µm, and 2.3-5.5 µm, using prism cross-dispersers (15 arcsec-long slits). Single order long slit (60 arcsec) modes are also available. A high throughput prism mode is a provided for 0.8-2.5 µm spectroscopy at R~100 for solid state features and SEDs. A Raytheon Aladdin 3 1024x1024 InSb array is used in the spectrograph. SpeX also contains an infrared slit-viewer/guider covering a 60x60arcsec field-of-view at 0.12arcsec/pixel. A Raytheon Aladdin 2 512x512 InSb array in the infrared slit-viewer. The infrared slit viewer can also be used for imaging or photometry. SpeX is used for a wide array of planetary and astrophysical research programs, and is the most requested instrument on IRTF. SpeX will be taken off of the telescope for about 6 months to upgrade its arrays starting in August 2012. iSHELL iSHELL is a 1 - 5.3 µm high resolution cross-dispersed echelle spectrograph which uses a 2048x2048 Hawaii-2RG infrared detector array. It replaced CSHELL; by using a larger array and a cross disperser, iShell has much larger wavelength coverage per setting than did CSHELL. iShell uses a silicion immersion grating to achieve a high dispersion with a relatively small grating, which in turn allows the optics and the whole instrument to be much smaller than if it used a conventional grating. Thus despite having much higher spectral resolution than SpeX, iShell will be slightly smaller. There will be two immersion gratings, one optimized for K band and one optimized for L band. Due to the silicon grating, iShell will not be sensitive to light shorter than 1 µm. Each pixel is 0.125" on the sky and the spectroscopic dispersion is 75,000 when used with a 0.375" slit. Five slits from 0.375" to 4.0" are available for use. iSHELL also has an IR imaging mode and IR guiding camera, which covers a 42" diameter field. As of 2019, iSHELL was the second-most heavily used instrument at IRTF (after SpeX). MIRSI MIRSI is a 2.2 to 25 µm thermal infrared imaging camera with grism spectrographic capability. MIRSI was built by Boston University and is now based at the IRTF. It is the only facility instrument that is cooled by liquid Helium, and