The ERTS-1 (renamed Landsat) and subsequent Landsats originally developed by NASA and operated by them and/or several other agencies from 1972 through the present (Landsat-7). The Landsat's two prime sensors, the MSS and TM. Approximately 13,300 sq. miles; 33,225 sq. km; 8,512,000 acres are enclosed in a Landsat MSS frame.