The Thematic Mapper (TM) is a multispectral earth resources sensor intended for application on NASA's Landsat D spacecraft. The performance requirements and design features of the TM have been presented previously in a number of papers. This paper will briefly review the performance requirements and the design features of TM; it will then deal in some depth with the problem of registration between spectral bands. A major performance feature of TM is its multispectral capability and the associated ability of the system to perform tasks involving classification. Registration of these spectral bands is primarily dependent on the ability of the scan mirror to provide a highly linear scan profile. This ability is presented in detail, along with a description of the phenomena causing deviations from linearity. Experimental data documenting the performance of the scan mirror are presented along with a technique of real time compensation for nonlinearities.