The National Airborne Sounder Testbed-Interferometer (NAST-I) is a high spectral resolution (0.25 cm-1) and high spatial resolution (0.13 km linear resolution per km of aircraft flight altitude, at nadir) scanning (2.3 km ground cross-track swath width per km of aircraft flight altitude) passive infrared (IR) Michelson interferometer sounding system that was developed to be flown on high-altitude aircraft to provide experimental observations needed to finalize the specifications and to test proposed designs and data processing algorithms for the Cross-track Infrared Sounder (CrIS) flying on the Suomi NPP (SNPP) and Joint Polar Satellite System (JPSS) platforms. Because the NAST-I infrared spectral radiance and temperature, humidity, trace species, cloud and surface property soundings have unprecedented spectral and high spatial resolution, respectively, the data can be used to support a variety of satellite sensor calibration / validation and atmospheric research programs. The NAST-I covers a spectral range from ~ 600-2900 cm-1 (3.5-16 microns) with 0.25 cm-1 spectral resolution, yielding more than 9000 spectral channels of radiance emission/absorption information. The NAST-I instrument has flown numerous science missions on the ER-2, WB-57, and Proteus aircraft, and the team has evaluated efforts needed to become operational on the DC-8. Most recently, NAST-I was part of the ER-2 science payload for the FIREX-AQ field campaign conducted during August, 2019 (https://www.esrl.noaa.gov/csl/projects/firex-aq/). Additional information can be obtained from Anna Noe (anna.m.noe@nasa.gov, 757-864-6466), Dr. Daniel Zhou (daniel.k.zhou@nasa.gov, 757-864-5663), or Dr. Allen Larar (Allen.M.Larar@nasa.gov, 757-864-5328).