The development of the National Polar-orbiting Operational Environmental Satellite (NPOESS) Visible Infrared Imager Radiometer Suite (VIIRS) design demonstrated the value of an end-to-end simulation of remote sensing systems. To arrive at a truly optimized system, Raytheon developed and refined a system simulation capability that can be applied to a number of other programs. This capability supports both instrument and algorithm design trades. The VIIRS effort included spectral modeling of various surface types, radiative transfer modeling of the atmosphere (sometimes incorporating observed atmospheric profiles), instrument spectral, spatial, and radiometric response, and a chain of environmental product retrieval algorithms. In this paper, we present a system simulation tool that has evolved from the VIIRS capability into a more general software package that runs both quickly and accurately. This tool can be used to simulate the behavior of any system that includes a scanning visible/infrared imager or radiometer and associated product retrieval algorithms. The tool has been validated against actual Moderate-resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR) outputs (both instrument-level and product-level) to illustrate the realism of the instrument modeling and environmental algorithm implementation. The package has also been reapplied to the VIIRS system design to deliver a snapshot of what can be expected when the VIIRS prototype is launched aboard the NPOESS Preparatory Project (NPP) in 2006. As an example, we present the system level characteristics of the red and near infrared (NIR) reflectances, as well as the Normalized Difference Vegetation Index (NDVI) product that can be derived from these reflectances.